cgroup.c 144.1 KB
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/*
 *  Generic process-grouping system.
 *
 *  Based originally on the cpuset system, extracted by Paul Menage
 *  Copyright (C) 2006 Google, Inc
 *
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 *  Notifications support
 *  Copyright (C) 2009 Nokia Corporation
 *  Author: Kirill A. Shutemov
 *
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 *  Copyright notices from the original cpuset code:
 *  --------------------------------------------------
 *  Copyright (C) 2003 BULL SA.
 *  Copyright (C) 2004-2006 Silicon Graphics, Inc.
 *
 *  Portions derived from Patrick Mochel's sysfs code.
 *  sysfs is Copyright (c) 2001-3 Patrick Mochel
 *
 *  2003-10-10 Written by Simon Derr.
 *  2003-10-22 Updates by Stephen Hemminger.
 *  2004 May-July Rework by Paul Jackson.
 *  ---------------------------------------------------
 *
 *  This file is subject to the terms and conditions of the GNU General Public
 *  License.  See the file COPYING in the main directory of the Linux
 *  distribution for more details.
 */

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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

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#include <linux/cgroup.h>
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#include <linux/cred.h>
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#include <linux/ctype.h>
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#include <linux/errno.h>
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#include <linux/init_task.h>
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#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/mm.h>
#include <linux/mutex.h>
#include <linux/mount.h>
#include <linux/pagemap.h>
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#include <linux/proc_fs.h>
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#include <linux/rcupdate.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
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#include <linux/rwsem.h>
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#include <linux/string.h>
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#include <linux/sort.h>
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#include <linux/kmod.h>
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#include <linux/delayacct.h>
#include <linux/cgroupstats.h>
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#include <linux/hashtable.h>
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#include <linux/pid_namespace.h>
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#include <linux/idr.h>
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#include <linux/vmalloc.h> /* TODO: replace with more sophisticated array */
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#include <linux/kthread.h>
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#include <linux/delay.h>
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#include <linux/atomic.h>
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/*
 * pidlists linger the following amount before being destroyed.  The goal
 * is avoiding frequent destruction in the middle of consecutive read calls
 * Expiring in the middle is a performance problem not a correctness one.
 * 1 sec should be enough.
 */
#define CGROUP_PIDLIST_DESTROY_DELAY	HZ

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#define CGROUP_FILE_NAME_MAX		(MAX_CGROUP_TYPE_NAMELEN +	\
					 MAX_CFTYPE_NAME + 2)

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/*
 * cgroup_tree_mutex nests above cgroup_mutex and protects cftypes, file
 * creation/removal and hierarchy changing operations including cgroup
 * creation, removal, css association and controller rebinding.  This outer
 * lock is needed mainly to resolve the circular dependency between kernfs
 * active ref and cgroup_mutex.  cgroup_tree_mutex nests above both.
 */
static DEFINE_MUTEX(cgroup_tree_mutex);

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/*
 * cgroup_mutex is the master lock.  Any modification to cgroup or its
 * hierarchy must be performed while holding it.
 *
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 * css_set_rwsem protects task->cgroups pointer, the list of css_set
 * objects, and the chain of tasks off each css_set.
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 *
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 * These locks are exported if CONFIG_PROVE_RCU so that accessors in
 * cgroup.h can use them for lockdep annotations.
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 */
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#ifdef CONFIG_PROVE_RCU
DEFINE_MUTEX(cgroup_mutex);
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DECLARE_RWSEM(css_set_rwsem);
EXPORT_SYMBOL_GPL(cgroup_mutex);
EXPORT_SYMBOL_GPL(css_set_rwsem);
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#else
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static DEFINE_MUTEX(cgroup_mutex);
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static DECLARE_RWSEM(css_set_rwsem);
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#endif

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/*
 * Protects cgroup_idr so that IDs can be released without grabbing
 * cgroup_mutex.
 */
static DEFINE_SPINLOCK(cgroup_idr_lock);

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/*
 * Protects cgroup_subsys->release_agent_path.  Modifying it also requires
 * cgroup_mutex.  Reading requires either cgroup_mutex or this spinlock.
 */
static DEFINE_SPINLOCK(release_agent_path_lock);
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#define cgroup_assert_mutexes_or_rcu_locked()				\
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	rcu_lockdep_assert(rcu_read_lock_held() ||			\
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			   lockdep_is_held(&cgroup_tree_mutex) ||	\
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			   lockdep_is_held(&cgroup_mutex),		\
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			   "cgroup_[tree_]mutex or RCU read lock required");
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/*
 * cgroup destruction makes heavy use of work items and there can be a lot
 * of concurrent destructions.  Use a separate workqueue so that cgroup
 * destruction work items don't end up filling up max_active of system_wq
 * which may lead to deadlock.
 */
static struct workqueue_struct *cgroup_destroy_wq;

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/*
 * pidlist destructions need to be flushed on cgroup destruction.  Use a
 * separate workqueue as flush domain.
 */
static struct workqueue_struct *cgroup_pidlist_destroy_wq;

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/* generate an array of cgroup subsystem pointers */
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#define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys,
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static struct cgroup_subsys *cgroup_subsys[] = {
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#include <linux/cgroup_subsys.h>
};
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#undef SUBSYS

/* array of cgroup subsystem names */
#define SUBSYS(_x) [_x ## _cgrp_id] = #_x,
static const char *cgroup_subsys_name[] = {
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#include <linux/cgroup_subsys.h>
};
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#undef SUBSYS
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/*
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 * The default hierarchy, reserved for the subsystems that are otherwise
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 * unattached - it never has more than a single cgroup, and all tasks are
 * part of that cgroup.
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 */
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struct cgroup_root cgrp_dfl_root;
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/*
 * The default hierarchy always exists but is hidden until mounted for the
 * first time.  This is for backward compatibility.
 */
static bool cgrp_dfl_root_visible;
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/* The list of hierarchy roots */

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static LIST_HEAD(cgroup_roots);
static int cgroup_root_count;
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/* hierarchy ID allocation and mapping, protected by cgroup_mutex */
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static DEFINE_IDR(cgroup_hierarchy_idr);
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/*
 * Assign a monotonically increasing serial number to cgroups.  It
 * guarantees cgroups with bigger numbers are newer than those with smaller
 * numbers.  Also, as cgroups are always appended to the parent's
 * ->children list, it guarantees that sibling cgroups are always sorted in
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 * the ascending serial number order on the list.  Protected by
 * cgroup_mutex.
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 */
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static u64 cgroup_serial_nr_next = 1;
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/* This flag indicates whether tasks in the fork and exit paths should
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 * check for fork/exit handlers to call. This avoids us having to do
 * extra work in the fork/exit path if none of the subsystems need to
 * be called.
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 */
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static int need_forkexit_callback __read_mostly;
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static struct cftype cgroup_base_files[];

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static void cgroup_put(struct cgroup *cgrp);
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static int rebind_subsystems(struct cgroup_root *dst_root,
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			     unsigned int ss_mask);
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static void cgroup_destroy_css_killed(struct cgroup *cgrp);
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static int cgroup_destroy_locked(struct cgroup *cgrp);
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static int create_css(struct cgroup *cgrp, struct cgroup_subsys *ss);
static void kill_css(struct cgroup_subsys_state *css);
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static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[],
			      bool is_add);
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static void cgroup_pidlist_destroy_all(struct cgroup *cgrp);
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/* IDR wrappers which synchronize using cgroup_idr_lock */
static int cgroup_idr_alloc(struct idr *idr, void *ptr, int start, int end,
			    gfp_t gfp_mask)
{
	int ret;

	idr_preload(gfp_mask);
	spin_lock(&cgroup_idr_lock);
	ret = idr_alloc(idr, ptr, start, end, gfp_mask);
	spin_unlock(&cgroup_idr_lock);
	idr_preload_end();
	return ret;
}

static void *cgroup_idr_replace(struct idr *idr, void *ptr, int id)
{
	void *ret;

	spin_lock(&cgroup_idr_lock);
	ret = idr_replace(idr, ptr, id);
	spin_unlock(&cgroup_idr_lock);
	return ret;
}

static void cgroup_idr_remove(struct idr *idr, int id)
{
	spin_lock(&cgroup_idr_lock);
	idr_remove(idr, id);
	spin_unlock(&cgroup_idr_lock);
}

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/**
 * cgroup_css - obtain a cgroup's css for the specified subsystem
 * @cgrp: the cgroup of interest
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 * @ss: the subsystem of interest (%NULL returns the dummy_css)
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 *
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 * Return @cgrp's css (cgroup_subsys_state) associated with @ss.  This
 * function must be called either under cgroup_mutex or rcu_read_lock() and
 * the caller is responsible for pinning the returned css if it wants to
 * keep accessing it outside the said locks.  This function may return
 * %NULL if @cgrp doesn't have @subsys_id enabled.
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 */
static struct cgroup_subsys_state *cgroup_css(struct cgroup *cgrp,
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					      struct cgroup_subsys *ss)
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{
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	if (ss)
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		return rcu_dereference_check(cgrp->subsys[ss->id],
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					lockdep_is_held(&cgroup_tree_mutex) ||
					lockdep_is_held(&cgroup_mutex));
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	else
		return &cgrp->dummy_css;
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}
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/**
 * cgroup_e_css - obtain a cgroup's effective css for the specified subsystem
 * @cgrp: the cgroup of interest
 * @ss: the subsystem of interest (%NULL returns the dummy_css)
 *
 * Similar to cgroup_css() but returns the effctive css, which is defined
 * as the matching css of the nearest ancestor including self which has @ss
 * enabled.  If @ss is associated with the hierarchy @cgrp is on, this
 * function is guaranteed to return non-NULL css.
 */
static struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgrp,
						struct cgroup_subsys *ss)
{
	lockdep_assert_held(&cgroup_mutex);

	if (!ss)
		return &cgrp->dummy_css;

	if (!(cgrp->root->subsys_mask & (1 << ss->id)))
		return NULL;

	while (cgrp->parent &&
	       !(cgrp->parent->child_subsys_mask & (1 << ss->id)))
		cgrp = cgrp->parent;

	return cgroup_css(cgrp, ss);
}

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/* convenient tests for these bits */
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static inline bool cgroup_is_dead(const struct cgroup *cgrp)
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{
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	return test_bit(CGRP_DEAD, &cgrp->flags);
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}

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struct cgroup_subsys_state *seq_css(struct seq_file *seq)
{
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	struct kernfs_open_file *of = seq->private;
	struct cgroup *cgrp = of->kn->parent->priv;
	struct cftype *cft = seq_cft(seq);

	/*
	 * This is open and unprotected implementation of cgroup_css().
	 * seq_css() is only called from a kernfs file operation which has
	 * an active reference on the file.  Because all the subsystem
	 * files are drained before a css is disassociated with a cgroup,
	 * the matching css from the cgroup's subsys table is guaranteed to
	 * be and stay valid until the enclosing operation is complete.
	 */
	if (cft->ss)
		return rcu_dereference_raw(cgrp->subsys[cft->ss->id]);
	else
		return &cgrp->dummy_css;
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}
EXPORT_SYMBOL_GPL(seq_css);

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/**
 * cgroup_is_descendant - test ancestry
 * @cgrp: the cgroup to be tested
 * @ancestor: possible ancestor of @cgrp
 *
 * Test whether @cgrp is a descendant of @ancestor.  It also returns %true
 * if @cgrp == @ancestor.  This function is safe to call as long as @cgrp
 * and @ancestor are accessible.
 */
bool cgroup_is_descendant(struct cgroup *cgrp, struct cgroup *ancestor)
{
	while (cgrp) {
		if (cgrp == ancestor)
			return true;
		cgrp = cgrp->parent;
	}
	return false;
}
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static int cgroup_is_releasable(const struct cgroup *cgrp)
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{
	const int bits =
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		(1 << CGRP_RELEASABLE) |
		(1 << CGRP_NOTIFY_ON_RELEASE);
	return (cgrp->flags & bits) == bits;
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}

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static int notify_on_release(const struct cgroup *cgrp)
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{
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	return test_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
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}

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/**
 * for_each_css - iterate all css's of a cgroup
 * @css: the iteration cursor
 * @ssid: the index of the subsystem, CGROUP_SUBSYS_COUNT after reaching the end
 * @cgrp: the target cgroup to iterate css's of
 *
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 * Should be called under cgroup_[tree_]mutex.
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 */
#define for_each_css(css, ssid, cgrp)					\
	for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++)	\
		if (!((css) = rcu_dereference_check(			\
				(cgrp)->subsys[(ssid)],			\
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				lockdep_is_held(&cgroup_tree_mutex) ||	\
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				lockdep_is_held(&cgroup_mutex)))) { }	\
		else

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/**
 * for_each_e_css - iterate all effective css's of a cgroup
 * @css: the iteration cursor
 * @ssid: the index of the subsystem, CGROUP_SUBSYS_COUNT after reaching the end
 * @cgrp: the target cgroup to iterate css's of
 *
 * Should be called under cgroup_[tree_]mutex.
 */
#define for_each_e_css(css, ssid, cgrp)					\
	for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++)	\
		if (!((css) = cgroup_e_css(cgrp, cgroup_subsys[(ssid)]))) \
			;						\
		else

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/**
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 * for_each_subsys - iterate all enabled cgroup subsystems
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 * @ss: the iteration cursor
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 * @ssid: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end
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 */
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#define for_each_subsys(ss, ssid)					\
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	for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT &&		\
	     (((ss) = cgroup_subsys[ssid]) || true); (ssid)++)
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/* iterate across the hierarchies */
#define for_each_root(root)						\
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	list_for_each_entry((root), &cgroup_roots, root_list)
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/* iterate over child cgrps, lock should be held throughout iteration */
#define cgroup_for_each_live_child(child, cgrp)				\
	list_for_each_entry((child), &(cgrp)->children, sibling)	\
		if (({ lockdep_assert_held(&cgroup_tree_mutex);		\
		       cgroup_is_dead(child); }))			\
			;						\
		else

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/**
 * cgroup_lock_live_group - take cgroup_mutex and check that cgrp is alive.
 * @cgrp: the cgroup to be checked for liveness
 *
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 * On success, returns true; the mutex should be later unlocked.  On
 * failure returns false with no lock held.
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 */
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static bool cgroup_lock_live_group(struct cgroup *cgrp)
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{
	mutex_lock(&cgroup_mutex);
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	if (cgroup_is_dead(cgrp)) {
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		mutex_unlock(&cgroup_mutex);
		return false;
	}
	return true;
}

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/* the list of cgroups eligible for automatic release. Protected by
 * release_list_lock */
static LIST_HEAD(release_list);
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static DEFINE_RAW_SPINLOCK(release_list_lock);
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static void cgroup_release_agent(struct work_struct *work);
static DECLARE_WORK(release_agent_work, cgroup_release_agent);
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static void check_for_release(struct cgroup *cgrp);
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/*
 * A cgroup can be associated with multiple css_sets as different tasks may
 * belong to different cgroups on different hierarchies.  In the other
 * direction, a css_set is naturally associated with multiple cgroups.
 * This M:N relationship is represented by the following link structure
 * which exists for each association and allows traversing the associations
 * from both sides.
 */
struct cgrp_cset_link {
	/* the cgroup and css_set this link associates */
	struct cgroup		*cgrp;
	struct css_set		*cset;

	/* list of cgrp_cset_links anchored at cgrp->cset_links */
	struct list_head	cset_link;

	/* list of cgrp_cset_links anchored at css_set->cgrp_links */
	struct list_head	cgrp_link;
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};

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/*
 * The default css_set - used by init and its children prior to any
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 * hierarchies being mounted. It contains a pointer to the root state
 * for each subsystem. Also used to anchor the list of css_sets. Not
 * reference-counted, to improve performance when child cgroups
 * haven't been created.
 */
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static struct css_set init_css_set = {
	.refcount		= ATOMIC_INIT(1),
	.cgrp_links		= LIST_HEAD_INIT(init_css_set.cgrp_links),
	.tasks			= LIST_HEAD_INIT(init_css_set.tasks),
	.mg_tasks		= LIST_HEAD_INIT(init_css_set.mg_tasks),
	.mg_preload_node	= LIST_HEAD_INIT(init_css_set.mg_preload_node),
	.mg_node		= LIST_HEAD_INIT(init_css_set.mg_node),
};
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static int css_set_count	= 1;	/* 1 for init_css_set */
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/**
 * cgroup_update_populated - updated populated count of a cgroup
 * @cgrp: the target cgroup
 * @populated: inc or dec populated count
 *
 * @cgrp is either getting the first task (css_set) or losing the last.
 * Update @cgrp->populated_cnt accordingly.  The count is propagated
 * towards root so that a given cgroup's populated_cnt is zero iff the
 * cgroup and all its descendants are empty.
 *
 * @cgrp's interface file "cgroup.populated" is zero if
 * @cgrp->populated_cnt is zero and 1 otherwise.  When @cgrp->populated_cnt
 * changes from or to zero, userland is notified that the content of the
 * interface file has changed.  This can be used to detect when @cgrp and
 * its descendants become populated or empty.
 */
static void cgroup_update_populated(struct cgroup *cgrp, bool populated)
{
	lockdep_assert_held(&css_set_rwsem);

	do {
		bool trigger;

		if (populated)
			trigger = !cgrp->populated_cnt++;
		else
			trigger = !--cgrp->populated_cnt;

		if (!trigger)
			break;

		if (cgrp->populated_kn)
			kernfs_notify(cgrp->populated_kn);
		cgrp = cgrp->parent;
	} while (cgrp);
}

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/*
 * hash table for cgroup groups. This improves the performance to find
 * an existing css_set. This hash doesn't (currently) take into
 * account cgroups in empty hierarchies.
 */
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#define CSS_SET_HASH_BITS	7
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static DEFINE_HASHTABLE(css_set_table, CSS_SET_HASH_BITS);
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static unsigned long css_set_hash(struct cgroup_subsys_state *css[])
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{
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	unsigned long key = 0UL;
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	struct cgroup_subsys *ss;
	int i;
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	for_each_subsys(ss, i)
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		key += (unsigned long)css[i];
	key = (key >> 16) ^ key;
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	return key;
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}

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static void put_css_set_locked(struct css_set *cset, bool taskexit)
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{
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	struct cgrp_cset_link *link, *tmp_link;
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	struct cgroup_subsys *ss;
	int ssid;
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	lockdep_assert_held(&css_set_rwsem);

	if (!atomic_dec_and_test(&cset->refcount))
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		return;
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	/* This css_set is dead. unlink it and release cgroup refcounts */
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	for_each_subsys(ss, ssid)
		list_del(&cset->e_cset_node[ssid]);
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	hash_del(&cset->hlist);
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	css_set_count--;

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	list_for_each_entry_safe(link, tmp_link, &cset->cgrp_links, cgrp_link) {
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		struct cgroup *cgrp = link->cgrp;
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		list_del(&link->cset_link);
		list_del(&link->cgrp_link);
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		/* @cgrp can't go away while we're holding css_set_rwsem */
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		if (list_empty(&cgrp->cset_links)) {
			cgroup_update_populated(cgrp, false);
			if (notify_on_release(cgrp)) {
				if (taskexit)
					set_bit(CGRP_RELEASABLE, &cgrp->flags);
				check_for_release(cgrp);
			}
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		}
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		kfree(link);
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	}
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	kfree_rcu(cset, rcu_head);
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}

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static void put_css_set(struct css_set *cset, bool taskexit)
{
	/*
	 * Ensure that the refcount doesn't hit zero while any readers
	 * can see it. Similar to atomic_dec_and_lock(), but for an
	 * rwlock
	 */
	if (atomic_add_unless(&cset->refcount, -1, 1))
		return;

	down_write(&css_set_rwsem);
	put_css_set_locked(cset, taskexit);
	up_write(&css_set_rwsem);
}

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/*
 * refcounted get/put for css_set objects
 */
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static inline void get_css_set(struct css_set *cset)
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{
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	atomic_inc(&cset->refcount);
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}

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/**
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 * compare_css_sets - helper function for find_existing_css_set().
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 * @cset: candidate css_set being tested
 * @old_cset: existing css_set for a task
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 * @new_cgrp: cgroup that's being entered by the task
 * @template: desired set of css pointers in css_set (pre-calculated)
 *
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 * Returns true if "cset" matches "old_cset" except for the hierarchy
581 582
 * which "new_cgrp" belongs to, for which it should match "new_cgrp".
 */
583 584
static bool compare_css_sets(struct css_set *cset,
			     struct css_set *old_cset,
585 586 587 588 589
			     struct cgroup *new_cgrp,
			     struct cgroup_subsys_state *template[])
{
	struct list_head *l1, *l2;

590 591 592 593 594 595
	/*
	 * On the default hierarchy, there can be csets which are
	 * associated with the same set of cgroups but different csses.
	 * Let's first ensure that csses match.
	 */
	if (memcmp(template, cset->subsys, sizeof(cset->subsys)))
596 597 598 599
		return false;

	/*
	 * Compare cgroup pointers in order to distinguish between
600 601 602
	 * different cgroups in hierarchies.  As different cgroups may
	 * share the same effective css, this comparison is always
	 * necessary.
603
	 */
604 605
	l1 = &cset->cgrp_links;
	l2 = &old_cset->cgrp_links;
606
	while (1) {
607
		struct cgrp_cset_link *link1, *link2;
608
		struct cgroup *cgrp1, *cgrp2;
609 610 611 612

		l1 = l1->next;
		l2 = l2->next;
		/* See if we reached the end - both lists are equal length. */
613 614
		if (l1 == &cset->cgrp_links) {
			BUG_ON(l2 != &old_cset->cgrp_links);
615 616
			break;
		} else {
617
			BUG_ON(l2 == &old_cset->cgrp_links);
618 619
		}
		/* Locate the cgroups associated with these links. */
620 621 622 623
		link1 = list_entry(l1, struct cgrp_cset_link, cgrp_link);
		link2 = list_entry(l2, struct cgrp_cset_link, cgrp_link);
		cgrp1 = link1->cgrp;
		cgrp2 = link2->cgrp;
624
		/* Hierarchies should be linked in the same order. */
625
		BUG_ON(cgrp1->root != cgrp2->root);
626 627 628 629 630 631 632 633

		/*
		 * If this hierarchy is the hierarchy of the cgroup
		 * that's changing, then we need to check that this
		 * css_set points to the new cgroup; if it's any other
		 * hierarchy, then this css_set should point to the
		 * same cgroup as the old css_set.
		 */
634 635
		if (cgrp1->root == new_cgrp->root) {
			if (cgrp1 != new_cgrp)
636 637
				return false;
		} else {
638
			if (cgrp1 != cgrp2)
639 640 641 642 643 644
				return false;
		}
	}
	return true;
}

645 646 647 648 649
/**
 * find_existing_css_set - init css array and find the matching css_set
 * @old_cset: the css_set that we're using before the cgroup transition
 * @cgrp: the cgroup that we're moving into
 * @template: out param for the new set of csses, should be clear on entry
650
 */
651 652 653
static struct css_set *find_existing_css_set(struct css_set *old_cset,
					struct cgroup *cgrp,
					struct cgroup_subsys_state *template[])
654
{
655
	struct cgroup_root *root = cgrp->root;
656
	struct cgroup_subsys *ss;
657
	struct css_set *cset;
658
	unsigned long key;
659
	int i;
660

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	/*
	 * Build the set of subsystem state objects that we want to see in the
	 * new css_set. while subsystems can change globally, the entries here
	 * won't change, so no need for locking.
	 */
666
	for_each_subsys(ss, i) {
667
		if (root->subsys_mask & (1UL << i)) {
668 669 670 671 672
			/*
			 * @ss is in this hierarchy, so we want the
			 * effective css from @cgrp.
			 */
			template[i] = cgroup_e_css(cgrp, ss);
673
		} else {
674 675 676 677
			/*
			 * @ss is not in this hierarchy, so we don't want
			 * to change the css.
			 */
678
			template[i] = old_cset->subsys[i];
679 680 681
		}
	}

682
	key = css_set_hash(template);
683 684
	hash_for_each_possible(css_set_table, cset, hlist, key) {
		if (!compare_css_sets(cset, old_cset, cgrp, template))
685 686 687
			continue;

		/* This css_set matches what we need */
688
		return cset;
689
	}
690 691 692 693 694

	/* No existing cgroup group matched */
	return NULL;
}

695
static void free_cgrp_cset_links(struct list_head *links_to_free)
696
{
697
	struct cgrp_cset_link *link, *tmp_link;
698

699 700
	list_for_each_entry_safe(link, tmp_link, links_to_free, cset_link) {
		list_del(&link->cset_link);
701 702 703 704
		kfree(link);
	}
}

705 706 707 708 709 710 711
/**
 * allocate_cgrp_cset_links - allocate cgrp_cset_links
 * @count: the number of links to allocate
 * @tmp_links: list_head the allocated links are put on
 *
 * Allocate @count cgrp_cset_link structures and chain them on @tmp_links
 * through ->cset_link.  Returns 0 on success or -errno.
712
 */
713
static int allocate_cgrp_cset_links(int count, struct list_head *tmp_links)
714
{
715
	struct cgrp_cset_link *link;
716
	int i;
717 718 719

	INIT_LIST_HEAD(tmp_links);

720
	for (i = 0; i < count; i++) {
721
		link = kzalloc(sizeof(*link), GFP_KERNEL);
722
		if (!link) {
723
			free_cgrp_cset_links(tmp_links);
724 725
			return -ENOMEM;
		}
726
		list_add(&link->cset_link, tmp_links);
727 728 729 730
	}
	return 0;
}

731 732
/**
 * link_css_set - a helper function to link a css_set to a cgroup
733
 * @tmp_links: cgrp_cset_link objects allocated by allocate_cgrp_cset_links()
734
 * @cset: the css_set to be linked
735 736
 * @cgrp: the destination cgroup
 */
737 738
static void link_css_set(struct list_head *tmp_links, struct css_set *cset,
			 struct cgroup *cgrp)
739
{
740
	struct cgrp_cset_link *link;
741

742
	BUG_ON(list_empty(tmp_links));
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	if (cgroup_on_dfl(cgrp))
		cset->dfl_cgrp = cgrp;

747 748
	link = list_first_entry(tmp_links, struct cgrp_cset_link, cset_link);
	link->cset = cset;
749
	link->cgrp = cgrp;
750 751 752

	if (list_empty(&cgrp->cset_links))
		cgroup_update_populated(cgrp, true);
753
	list_move(&link->cset_link, &cgrp->cset_links);
754

755 756 757 758
	/*
	 * Always add links to the tail of the list so that the list
	 * is sorted by order of hierarchy creation
	 */
759
	list_add_tail(&link->cgrp_link, &cset->cgrp_links);
760 761
}

762 763 764 765 766 767 768
/**
 * find_css_set - return a new css_set with one cgroup updated
 * @old_cset: the baseline css_set
 * @cgrp: the cgroup to be updated
 *
 * Return a new css_set that's equivalent to @old_cset, but with @cgrp
 * substituted into the appropriate hierarchy.
769
 */
770 771
static struct css_set *find_css_set(struct css_set *old_cset,
				    struct cgroup *cgrp)
772
{
773
	struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT] = { };
774
	struct css_set *cset;
775 776
	struct list_head tmp_links;
	struct cgrp_cset_link *link;
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	struct cgroup_subsys *ss;
778
	unsigned long key;
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	int ssid;
780

781 782
	lockdep_assert_held(&cgroup_mutex);

783 784
	/* First see if we already have a cgroup group that matches
	 * the desired set */
785
	down_read(&css_set_rwsem);
786 787 788
	cset = find_existing_css_set(old_cset, cgrp, template);
	if (cset)
		get_css_set(cset);
789
	up_read(&css_set_rwsem);
790

791 792
	if (cset)
		return cset;
793

794
	cset = kzalloc(sizeof(*cset), GFP_KERNEL);
795
	if (!cset)
796 797
		return NULL;

798
	/* Allocate all the cgrp_cset_link objects that we'll need */
799
	if (allocate_cgrp_cset_links(cgroup_root_count, &tmp_links) < 0) {
800
		kfree(cset);
801 802 803
		return NULL;
	}

804
	atomic_set(&cset->refcount, 1);
805
	INIT_LIST_HEAD(&cset->cgrp_links);
806
	INIT_LIST_HEAD(&cset->tasks);
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	INIT_LIST_HEAD(&cset->mg_tasks);
808
	INIT_LIST_HEAD(&cset->mg_preload_node);
809
	INIT_LIST_HEAD(&cset->mg_node);
810
	INIT_HLIST_NODE(&cset->hlist);
811 812 813

	/* Copy the set of subsystem state objects generated in
	 * find_existing_css_set() */
814
	memcpy(cset->subsys, template, sizeof(cset->subsys));
815

816
	down_write(&css_set_rwsem);
817
	/* Add reference counts and links from the new css_set. */
818
	list_for_each_entry(link, &old_cset->cgrp_links, cgrp_link) {
819
		struct cgroup *c = link->cgrp;
820

821 822
		if (c->root == cgrp->root)
			c = cgrp;
823
		link_css_set(&tmp_links, cset, c);
824
	}
825

826
	BUG_ON(!list_empty(&tmp_links));
827 828

	css_set_count++;
829

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	/* Add @cset to the hash table */
831 832
	key = css_set_hash(cset->subsys);
	hash_add(css_set_table, &cset->hlist, key);
833

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	for_each_subsys(ss, ssid)
		list_add_tail(&cset->e_cset_node[ssid],
			      &cset->subsys[ssid]->cgroup->e_csets[ssid]);

838
	up_write(&css_set_rwsem);
839

840
	return cset;
841 842
}

843
static struct cgroup_root *cgroup_root_from_kf(struct kernfs_root *kf_root)
844
{
845
	struct cgroup *root_cgrp = kf_root->kn->priv;
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847
	return root_cgrp->root;
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}

850
static int cgroup_init_root_id(struct cgroup_root *root)
851 852 853 854 855
{
	int id;

	lockdep_assert_held(&cgroup_mutex);

856
	id = idr_alloc_cyclic(&cgroup_hierarchy_idr, root, 0, 0, GFP_KERNEL);
857 858 859 860 861 862 863
	if (id < 0)
		return id;

	root->hierarchy_id = id;
	return 0;
}

864
static void cgroup_exit_root_id(struct cgroup_root *root)
865 866 867 868 869 870 871 872 873
{
	lockdep_assert_held(&cgroup_mutex);

	if (root->hierarchy_id) {
		idr_remove(&cgroup_hierarchy_idr, root->hierarchy_id);
		root->hierarchy_id = 0;
	}
}

874
static void cgroup_free_root(struct cgroup_root *root)
875 876 877 878 879 880 881 882 883 884
{
	if (root) {
		/* hierarhcy ID shoulid already have been released */
		WARN_ON_ONCE(root->hierarchy_id);

		idr_destroy(&root->cgroup_idr);
		kfree(root);
	}
}

885
static void cgroup_destroy_root(struct cgroup_root *root)
886
{
887
	struct cgroup *cgrp = &root->cgrp;
888 889
	struct cgrp_cset_link *link, *tmp_link;

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	mutex_lock(&cgroup_tree_mutex);
	mutex_lock(&cgroup_mutex);
892

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	BUG_ON(atomic_read(&root->nr_cgrps));
894 895 896
	BUG_ON(!list_empty(&cgrp->children));

	/* Rebind all subsystems back to the default hierarchy */
897
	rebind_subsystems(&cgrp_dfl_root, root->subsys_mask);
898 899

	/*
900 901
	 * Release all the links from cset_links to this hierarchy's
	 * root cgroup
902
	 */
903
	down_write(&css_set_rwsem);
904 905 906 907 908 909

	list_for_each_entry_safe(link, tmp_link, &cgrp->cset_links, cset_link) {
		list_del(&link->cset_link);
		list_del(&link->cgrp_link);
		kfree(link);
	}
910
	up_write(&css_set_rwsem);
911 912 913 914 915 916 917 918 919 920 921

	if (!list_empty(&root->root_list)) {
		list_del(&root->root_list);
		cgroup_root_count--;
	}

	cgroup_exit_root_id(root);

	mutex_unlock(&cgroup_mutex);
	mutex_unlock(&cgroup_tree_mutex);

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	kernfs_destroy_root(root->kf_root);
923 924 925
	cgroup_free_root(root);
}

926 927
/* look up cgroup associated with given css_set on the specified hierarchy */
static struct cgroup *cset_cgroup_from_root(struct css_set *cset,
928
					    struct cgroup_root *root)
929 930 931
{
	struct cgroup *res = NULL;

932 933 934
	lockdep_assert_held(&cgroup_mutex);
	lockdep_assert_held(&css_set_rwsem);

935
	if (cset == &init_css_set) {
936
		res = &root->cgrp;
937
	} else {
938 939 940
		struct cgrp_cset_link *link;

		list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
941
			struct cgroup *c = link->cgrp;
942

943 944 945 946 947 948
			if (c->root == root) {
				res = c;
				break;
			}
		}
	}
949

950 951 952 953
	BUG_ON(!res);
	return res;
}

954
/*
955 956 957 958
 * Return the cgroup for "task" from the given hierarchy. Must be
 * called with cgroup_mutex and css_set_rwsem held.
 */
static struct cgroup *task_cgroup_from_root(struct task_struct *task,
959
					    struct cgroup_root *root)
960 961 962 963 964 965 966 967 968
{
	/*
	 * No need to lock the task - since we hold cgroup_mutex the
	 * task can't change groups, so the only thing that can happen
	 * is that it exits and its css is set back to init_css_set.
	 */
	return cset_cgroup_from_root(task_css_set(task), root);
}

969 970 971 972 973 974
/*
 * A task must hold cgroup_mutex to modify cgroups.
 *
 * Any task can increment and decrement the count field without lock.
 * So in general, code holding cgroup_mutex can't rely on the count
 * field not changing.  However, if the count goes to zero, then only
975
 * cgroup_attach_task() can increment it again.  Because a count of zero
976 977 978 979 980 981 982 983 984 985 986 987 988
 * means that no tasks are currently attached, therefore there is no
 * way a task attached to that cgroup can fork (the other way to
 * increment the count).  So code holding cgroup_mutex can safely
 * assume that if the count is zero, it will stay zero. Similarly, if
 * a task holds cgroup_mutex on a cgroup with zero count, it
 * knows that the cgroup won't be removed, as cgroup_rmdir()
 * needs that mutex.
 *
 * The fork and exit callbacks cgroup_fork() and cgroup_exit(), don't
 * (usually) take cgroup_mutex.  These are the two most performance
 * critical pieces of code here.  The exception occurs on cgroup_exit(),
 * when a task in a notify_on_release cgroup exits.  Then cgroup_mutex
 * is taken, and if the cgroup count is zero, a usermode call made
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 * to the release agent with the name of the cgroup (path relative to
 * the root of cgroup file system) as the argument.
991 992 993 994
 *
 * A cgroup can only be deleted if both its 'count' of using tasks
 * is zero, and its list of 'children' cgroups is empty.  Since all
 * tasks in the system use _some_ cgroup, and since there is always at
995
 * least one task in the system (init, pid == 1), therefore, root cgroup
996
 * always has either children cgroups and/or using tasks.  So we don't
997
 * need a special hack to ensure that root cgroup cannot be deleted.
998 999
 *
 * P.S.  One more locking exception.  RCU is used to guard the
1000
 * update of a tasks cgroup pointer by cgroup_attach_task()
1001 1002
 */

1003
static int cgroup_populate_dir(struct cgroup *cgrp, unsigned int subsys_mask);
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static struct kernfs_syscall_ops cgroup_kf_syscall_ops;
1005
static const struct file_operations proc_cgroupstats_operations;
1006

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static char *cgroup_file_name(struct cgroup *cgrp, const struct cftype *cft,
			      char *buf)
1009
{
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	if (cft->ss && !(cft->flags & CFTYPE_NO_PREFIX) &&
	    !(cgrp->root->flags & CGRP_ROOT_NOPREFIX))
		snprintf(buf, CGROUP_FILE_NAME_MAX, "%s.%s",
			 cft->ss->name, cft->name);
	else
		strncpy(buf, cft->name, CGROUP_FILE_NAME_MAX);
	return buf;
1017 1018
}

1019 1020 1021 1022 1023 1024 1025 1026 1027 1028
/**
 * cgroup_file_mode - deduce file mode of a control file
 * @cft: the control file in question
 *
 * returns cft->mode if ->mode is not 0
 * returns S_IRUGO|S_IWUSR if it has both a read and a write handler
 * returns S_IRUGO if it has only a read handler
 * returns S_IWUSR if it has only a write hander
 */
static umode_t cgroup_file_mode(const struct cftype *cft)
1029
{
1030
	umode_t mode = 0;
1031

1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042
	if (cft->mode)
		return cft->mode;

	if (cft->read_u64 || cft->read_s64 || cft->seq_show)
		mode |= S_IRUGO;

	if (cft->write_u64 || cft->write_s64 || cft->write_string ||
	    cft->trigger)
		mode |= S_IWUSR;

	return mode;
1043 1044
}

1045 1046
static void cgroup_free_fn(struct work_struct *work)
{
1047
	struct cgroup *cgrp = container_of(work, struct cgroup, destroy_work);
1048

1049
	atomic_dec(&cgrp->root->nr_cgrps);
1050
	cgroup_pidlist_destroy_all(cgrp);
1051

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	if (cgrp->parent) {
		/*
		 * We get a ref to the parent, and put the ref when this
		 * cgroup is being freed, so it's guaranteed that the
		 * parent won't be destroyed before its children.
		 */
		cgroup_put(cgrp->parent);
		kernfs_put(cgrp->kn);
		kfree(cgrp);
	} else {
		/*
1063
		 * This is root cgroup's refcnt reaching zero, which
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1064 1065 1066 1067
		 * indicates that the root should be released.
		 */
		cgroup_destroy_root(cgrp->root);
	}
1068 1069 1070 1071 1072 1073
}

static void cgroup_free_rcu(struct rcu_head *head)
{
	struct cgroup *cgrp = container_of(head, struct cgroup, rcu_head);

1074
	INIT_WORK(&cgrp->destroy_work, cgroup_free_fn);
1075
	queue_work(cgroup_destroy_wq, &cgrp->destroy_work);
1076 1077
}

1078
static void cgroup_get(struct cgroup *cgrp)
1079
{
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	WARN_ON_ONCE(cgroup_is_dead(cgrp));
	WARN_ON_ONCE(atomic_read(&cgrp->refcnt) <= 0);
	atomic_inc(&cgrp->refcnt);
1083 1084
}

1085
static void cgroup_put(struct cgroup *cgrp)
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1086
{
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1087 1088
	if (!atomic_dec_and_test(&cgrp->refcnt))
		return;
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1089
	if (WARN_ON_ONCE(cgrp->parent && !cgroup_is_dead(cgrp)))
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		return;
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1092
	/*
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	 * XXX: cgrp->id is only used to look up css's.  As cgroup and
	 * css's lifetimes will be decoupled, it should be made
	 * per-subsystem and moved to css->id so that lookups are
	 * successful until the target css is released.
1097
	 */
1098
	cgroup_idr_remove(&cgrp->root->cgroup_idr, cgrp->id);
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	cgrp->id = -1;
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1101
	call_rcu(&cgrp->rcu_head, cgroup_free_rcu);
1102
}
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1104
static void cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft)
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1105
{
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1106
	char name[CGROUP_FILE_NAME_MAX];
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1107

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1108
	lockdep_assert_held(&cgroup_tree_mutex);
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	kernfs_remove_by_name(cgrp->kn, cgroup_file_name(cgrp, cft, name));
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}

1112
/**
1113
 * cgroup_clear_dir - remove subsys files in a cgroup directory
1114
 * @cgrp: target cgroup
1115 1116
 * @subsys_mask: mask of the subsystem ids whose files should be removed
 */
1117
static void cgroup_clear_dir(struct cgroup *cgrp, unsigned int subsys_mask)
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1118
{
1119
	struct cgroup_subsys *ss;
1120
	int i;
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1121

1122
	for_each_subsys(ss, i) {
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1123
		struct cftype *cfts;
1124

1125
		if (!(subsys_mask & (1 << i)))
1126
			continue;
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		list_for_each_entry(cfts, &ss->cfts, node)
			cgroup_addrm_files(cgrp, cfts, false);
1129
	}
1130 1131
}

1132
static int rebind_subsystems(struct cgroup_root *dst_root, unsigned int ss_mask)
1133
{
1134
	struct cgroup_subsys *ss;
T
Tejun Heo 已提交
1135
	int ssid, i, ret;
1136

T
Tejun Heo 已提交
1137 1138
	lockdep_assert_held(&cgroup_tree_mutex);
	lockdep_assert_held(&cgroup_mutex);
1139

1140 1141 1142
	for_each_subsys(ss, ssid) {
		if (!(ss_mask & (1 << ssid)))
			continue;
B
Ben Blum 已提交
1143

1144 1145
		/* if @ss has non-root csses attached to it, can't move */
		if (css_next_child(NULL, cgroup_css(&ss->root->cgrp, ss)))
T
Tejun Heo 已提交
1146
			return -EBUSY;
1147

1148
		/* can't move between two non-dummy roots either */
1149
		if (ss->root != &cgrp_dfl_root && dst_root != &cgrp_dfl_root)
1150
			return -EBUSY;
1151 1152
	}

T
Tejun Heo 已提交
1153 1154 1155
	ret = cgroup_populate_dir(&dst_root->cgrp, ss_mask);
	if (ret) {
		if (dst_root != &cgrp_dfl_root)
1156
			return ret;
1157

T
Tejun Heo 已提交
1158 1159 1160 1161 1162 1163 1164
		/*
		 * Rebinding back to the default root is not allowed to
		 * fail.  Using both default and non-default roots should
		 * be rare.  Moving subsystems back and forth even more so.
		 * Just warn about it and continue.
		 */
		if (cgrp_dfl_root_visible) {
1165
			pr_warn("failed to create files (%d) while rebinding 0x%x to default root\n",
1166
				ret, ss_mask);
1167
			pr_warn("you may retry by moving them to a different hierarchy and unbinding\n");
T
Tejun Heo 已提交
1168
		}
1169
	}
1170 1171 1172 1173 1174

	/*
	 * Nothing can fail from this point on.  Remove files for the
	 * removed subsystems and rebind each subsystem.
	 */
1175
	mutex_unlock(&cgroup_mutex);
1176
	for_each_subsys(ss, ssid)
T
Tejun Heo 已提交
1177
		if (ss_mask & (1 << ssid))
1178
			cgroup_clear_dir(&ss->root->cgrp, 1 << ssid);
1179
	mutex_lock(&cgroup_mutex);
1180

1181
	for_each_subsys(ss, ssid) {
1182
		struct cgroup_root *src_root;
1183
		struct cgroup_subsys_state *css;
T
Tejun Heo 已提交
1184
		struct css_set *cset;
1185

1186 1187
		if (!(ss_mask & (1 << ssid)))
			continue;
1188

1189
		src_root = ss->root;
1190
		css = cgroup_css(&src_root->cgrp, ss);
1191

1192
		WARN_ON(!css || cgroup_css(&dst_root->cgrp, ss));
1193

1194 1195
		RCU_INIT_POINTER(src_root->cgrp.subsys[ssid], NULL);
		rcu_assign_pointer(dst_root->cgrp.subsys[ssid], css);
1196
		ss->root = dst_root;
1197
		css->cgroup = &dst_root->cgrp;
1198

T
Tejun Heo 已提交
1199 1200 1201 1202 1203 1204
		down_write(&css_set_rwsem);
		hash_for_each(css_set_table, i, cset, hlist)
			list_move_tail(&cset->e_cset_node[ss->id],
				       &dst_root->cgrp.e_csets[ss->id]);
		up_write(&css_set_rwsem);

1205 1206 1207
		src_root->subsys_mask &= ~(1 << ssid);
		src_root->cgrp.child_subsys_mask &= ~(1 << ssid);

1208
		/* default hierarchy doesn't enable controllers by default */
1209
		dst_root->subsys_mask |= 1 << ssid;
1210 1211
		if (dst_root != &cgrp_dfl_root)
			dst_root->cgrp.child_subsys_mask |= 1 << ssid;
1212

1213 1214
		if (ss->bind)
			ss->bind(css);
1215 1216
	}

T
Tejun Heo 已提交
1217
	kernfs_activate(dst_root->cgrp.kn);
1218 1219 1220
	return 0;
}

T
Tejun Heo 已提交
1221 1222
static int cgroup_show_options(struct seq_file *seq,
			       struct kernfs_root *kf_root)
1223
{
1224
	struct cgroup_root *root = cgroup_root_from_kf(kf_root);
1225
	struct cgroup_subsys *ss;
T
Tejun Heo 已提交
1226
	int ssid;
1227

T
Tejun Heo 已提交
1228
	for_each_subsys(ss, ssid)
1229
		if (root->subsys_mask & (1 << ssid))
T
Tejun Heo 已提交
1230
			seq_printf(seq, ",%s", ss->name);
1231 1232
	if (root->flags & CGRP_ROOT_SANE_BEHAVIOR)
		seq_puts(seq, ",sane_behavior");
1233
	if (root->flags & CGRP_ROOT_NOPREFIX)
1234
		seq_puts(seq, ",noprefix");
1235
	if (root->flags & CGRP_ROOT_XATTR)
A
Aristeu Rozanski 已提交
1236
		seq_puts(seq, ",xattr");
1237 1238

	spin_lock(&release_agent_path_lock);
1239 1240
	if (strlen(root->release_agent_path))
		seq_printf(seq, ",release_agent=%s", root->release_agent_path);
1241 1242
	spin_unlock(&release_agent_path_lock);

1243
	if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags))
1244
		seq_puts(seq, ",clone_children");
1245 1246
	if (strlen(root->name))
		seq_printf(seq, ",name=%s", root->name);
1247 1248 1249 1250
	return 0;
}

struct cgroup_sb_opts {
1251 1252
	unsigned int subsys_mask;
	unsigned int flags;
1253
	char *release_agent;
1254
	bool cpuset_clone_children;
1255
	char *name;
1256 1257
	/* User explicitly requested empty subsystem */
	bool none;
1258 1259
};

B
Ben Blum 已提交
1260
static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
1261
{
1262 1263
	char *token, *o = data;
	bool all_ss = false, one_ss = false;
1264
	unsigned int mask = -1U;
1265 1266
	struct cgroup_subsys *ss;
	int i;
1267 1268

#ifdef CONFIG_CPUSETS
1269
	mask = ~(1U << cpuset_cgrp_id);
1270
#endif
1271

1272
	memset(opts, 0, sizeof(*opts));
1273 1274 1275 1276

	while ((token = strsep(&o, ",")) != NULL) {
		if (!*token)
			return -EINVAL;
1277
		if (!strcmp(token, "none")) {
1278 1279
			/* Explicitly have no subsystems */
			opts->none = true;
1280 1281 1282 1283 1284 1285 1286 1287 1288
			continue;
		}
		if (!strcmp(token, "all")) {
			/* Mutually exclusive option 'all' + subsystem name */
			if (one_ss)
				return -EINVAL;
			all_ss = true;
			continue;
		}
1289 1290 1291 1292
		if (!strcmp(token, "__DEVEL__sane_behavior")) {
			opts->flags |= CGRP_ROOT_SANE_BEHAVIOR;
			continue;
		}
1293
		if (!strcmp(token, "noprefix")) {
1294
			opts->flags |= CGRP_ROOT_NOPREFIX;
1295 1296 1297
			continue;
		}
		if (!strcmp(token, "clone_children")) {
1298
			opts->cpuset_clone_children = true;
1299 1300
			continue;
		}
A
Aristeu Rozanski 已提交
1301
		if (!strcmp(token, "xattr")) {
1302
			opts->flags |= CGRP_ROOT_XATTR;
A
Aristeu Rozanski 已提交
1303 1304
			continue;
		}
1305
		if (!strncmp(token, "release_agent=", 14)) {
1306 1307 1308
			/* Specifying two release agents is forbidden */
			if (opts->release_agent)
				return -EINVAL;
1309
			opts->release_agent =
1310
				kstrndup(token + 14, PATH_MAX - 1, GFP_KERNEL);
1311 1312
			if (!opts->release_agent)
				return -ENOMEM;
1313 1314 1315
			continue;
		}
		if (!strncmp(token, "name=", 5)) {
1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329 1330 1331 1332
			const char *name = token + 5;
			/* Can't specify an empty name */
			if (!strlen(name))
				return -EINVAL;
			/* Must match [\w.-]+ */
			for (i = 0; i < strlen(name); i++) {
				char c = name[i];
				if (isalnum(c))
					continue;
				if ((c == '.') || (c == '-') || (c == '_'))
					continue;
				return -EINVAL;
			}
			/* Specifying two names is forbidden */
			if (opts->name)
				return -EINVAL;
			opts->name = kstrndup(name,
1333
					      MAX_CGROUP_ROOT_NAMELEN - 1,
1334 1335 1336
					      GFP_KERNEL);
			if (!opts->name)
				return -ENOMEM;
1337 1338 1339 1340

			continue;
		}

1341
		for_each_subsys(ss, i) {
1342 1343 1344 1345 1346 1347 1348 1349
			if (strcmp(token, ss->name))
				continue;
			if (ss->disabled)
				continue;

			/* Mutually exclusive option 'all' + subsystem name */
			if (all_ss)
				return -EINVAL;
1350
			opts->subsys_mask |= (1 << i);
1351 1352 1353 1354 1355 1356 1357 1358
			one_ss = true;

			break;
		}
		if (i == CGROUP_SUBSYS_COUNT)
			return -ENOENT;
	}

1359 1360
	/* Consistency checks */

1361
	if (opts->flags & CGRP_ROOT_SANE_BEHAVIOR) {
1362
		pr_warn("sane_behavior: this is still under development and its behaviors will change, proceed at your own risk\n");
1363

1364 1365 1366
		if ((opts->flags & (CGRP_ROOT_NOPREFIX | CGRP_ROOT_XATTR)) ||
		    opts->cpuset_clone_children || opts->release_agent ||
		    opts->name) {
1367
			pr_err("sane_behavior: noprefix, xattr, clone_children, release_agent and name are not allowed\n");
1368 1369
			return -EINVAL;
		}
T
Tejun Heo 已提交
1370 1371 1372 1373 1374 1375 1376 1377 1378
	} else {
		/*
		 * If the 'all' option was specified select all the
		 * subsystems, otherwise if 'none', 'name=' and a subsystem
		 * name options were not specified, let's default to 'all'
		 */
		if (all_ss || (!one_ss && !opts->none && !opts->name))
			for_each_subsys(ss, i)
				if (!ss->disabled)
1379
					opts->subsys_mask |= (1 << i);
1380

T
Tejun Heo 已提交
1381 1382 1383 1384 1385
		/*
		 * We either have to specify by name or by subsystems. (So
		 * all empty hierarchies must have a name).
		 */
		if (!opts->subsys_mask && !opts->name)
1386 1387 1388
			return -EINVAL;
	}

1389 1390 1391 1392 1393
	/*
	 * Option noprefix was introduced just for backward compatibility
	 * with the old cpuset, so we allow noprefix only if mounting just
	 * the cpuset subsystem.
	 */
1394
	if ((opts->flags & CGRP_ROOT_NOPREFIX) && (opts->subsys_mask & mask))
1395 1396
		return -EINVAL;

1397 1398

	/* Can't specify "none" and some subsystems */
1399
	if (opts->subsys_mask && opts->none)
1400 1401
		return -EINVAL;

1402 1403 1404
	return 0;
}

T
Tejun Heo 已提交
1405
static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data)
1406 1407
{
	int ret = 0;
1408
	struct cgroup_root *root = cgroup_root_from_kf(kf_root);
1409
	struct cgroup_sb_opts opts;
1410
	unsigned int added_mask, removed_mask;
1411

1412
	if (root->flags & CGRP_ROOT_SANE_BEHAVIOR) {
1413
		pr_err("sane_behavior: remount is not allowed\n");
1414 1415 1416
		return -EINVAL;
	}

T
Tejun Heo 已提交
1417
	mutex_lock(&cgroup_tree_mutex);
1418 1419 1420 1421 1422 1423 1424
	mutex_lock(&cgroup_mutex);

	/* See what subsystems are wanted */
	ret = parse_cgroupfs_options(data, &opts);
	if (ret)
		goto out_unlock;

1425
	if (opts.subsys_mask != root->subsys_mask || opts.release_agent)
1426
		pr_warn("option changes via remount are deprecated (pid=%d comm=%s)\n",
1427
			task_tgid_nr(current), current->comm);
1428

1429 1430
	added_mask = opts.subsys_mask & ~root->subsys_mask;
	removed_mask = root->subsys_mask & ~opts.subsys_mask;
1431

B
Ben Blum 已提交
1432
	/* Don't allow flags or name to change at remount */
1433
	if (((opts.flags ^ root->flags) & CGRP_ROOT_OPTION_MASK) ||
B
Ben Blum 已提交
1434
	    (opts.name && strcmp(opts.name, root->name))) {
1435
		pr_err("option or name mismatch, new: 0x%x \"%s\", old: 0x%x \"%s\"\n",
1436 1437
		       opts.flags & CGRP_ROOT_OPTION_MASK, opts.name ?: "",
		       root->flags & CGRP_ROOT_OPTION_MASK, root->name);
1438 1439 1440 1441
		ret = -EINVAL;
		goto out_unlock;
	}

1442
	/* remounting is not allowed for populated hierarchies */
1443
	if (!list_empty(&root->cgrp.children)) {
1444
		ret = -EBUSY;
1445
		goto out_unlock;
B
Ben Blum 已提交
1446
	}
1447

1448
	ret = rebind_subsystems(root, added_mask);
1449
	if (ret)
1450
		goto out_unlock;
1451

1452
	rebind_subsystems(&cgrp_dfl_root, removed_mask);
1453

1454 1455
	if (opts.release_agent) {
		spin_lock(&release_agent_path_lock);
1456
		strcpy(root->release_agent_path, opts.release_agent);
1457 1458
		spin_unlock(&release_agent_path_lock);
	}
1459
 out_unlock:
1460
	kfree(opts.release_agent);
1461
	kfree(opts.name);
1462
	mutex_unlock(&cgroup_mutex);
T
Tejun Heo 已提交
1463
	mutex_unlock(&cgroup_tree_mutex);
1464 1465 1466
	return ret;
}

1467 1468 1469 1470 1471 1472 1473 1474 1475 1476 1477 1478
/*
 * To reduce the fork() overhead for systems that are not actually using
 * their cgroups capability, we don't maintain the lists running through
 * each css_set to its tasks until we see the list actually used - in other
 * words after the first mount.
 */
static bool use_task_css_set_links __read_mostly;

static void cgroup_enable_task_cg_lists(void)
{
	struct task_struct *p, *g;

1479
	down_write(&css_set_rwsem);
1480 1481 1482 1483 1484 1485 1486 1487 1488 1489 1490 1491 1492 1493 1494 1495 1496 1497 1498 1499 1500 1501

	if (use_task_css_set_links)
		goto out_unlock;

	use_task_css_set_links = true;

	/*
	 * We need tasklist_lock because RCU is not safe against
	 * while_each_thread(). Besides, a forking task that has passed
	 * cgroup_post_fork() without seeing use_task_css_set_links = 1
	 * is not guaranteed to have its child immediately visible in the
	 * tasklist if we walk through it with RCU.
	 */
	read_lock(&tasklist_lock);
	do_each_thread(g, p) {
		WARN_ON_ONCE(!list_empty(&p->cg_list) ||
			     task_css_set(p) != &init_css_set);

		/*
		 * We should check if the process is exiting, otherwise
		 * it will race with cgroup_exit() in that the list
		 * entry won't be deleted though the process has exited.
1502 1503
		 * Do it while holding siglock so that we don't end up
		 * racing against cgroup_exit().
1504
		 */
1505
		spin_lock_irq(&p->sighand->siglock);
1506 1507 1508 1509 1510 1511
		if (!(p->flags & PF_EXITING)) {
			struct css_set *cset = task_css_set(p);

			list_add(&p->cg_list, &cset->tasks);
			get_css_set(cset);
		}
1512
		spin_unlock_irq(&p->sighand->siglock);
1513 1514 1515
	} while_each_thread(g, p);
	read_unlock(&tasklist_lock);
out_unlock:
1516
	up_write(&css_set_rwsem);
1517
}
1518

1519 1520
static void init_cgroup_housekeeping(struct cgroup *cgrp)
{
T
Tejun Heo 已提交
1521 1522 1523
	struct cgroup_subsys *ss;
	int ssid;

T
Tejun Heo 已提交
1524
	atomic_set(&cgrp->refcnt, 1);
1525 1526
	INIT_LIST_HEAD(&cgrp->sibling);
	INIT_LIST_HEAD(&cgrp->children);
1527
	INIT_LIST_HEAD(&cgrp->cset_links);
1528
	INIT_LIST_HEAD(&cgrp->release_list);
1529 1530
	INIT_LIST_HEAD(&cgrp->pidlists);
	mutex_init(&cgrp->pidlist_mutex);
T
Tejun Heo 已提交
1531
	cgrp->dummy_css.cgroup = cgrp;
T
Tejun Heo 已提交
1532 1533 1534

	for_each_subsys(ss, ssid)
		INIT_LIST_HEAD(&cgrp->e_csets[ssid]);
1535 1536

	init_waitqueue_head(&cgrp->offline_waitq);
1537
}
1538

1539
static void init_cgroup_root(struct cgroup_root *root,
1540
			     struct cgroup_sb_opts *opts)
1541
{
1542
	struct cgroup *cgrp = &root->cgrp;
1543

1544
	INIT_LIST_HEAD(&root->root_list);
1545
	atomic_set(&root->nr_cgrps, 1);
1546
	cgrp->root = root;
1547
	init_cgroup_housekeeping(cgrp);
1548
	idr_init(&root->cgroup_idr);
1549 1550 1551 1552 1553 1554

	root->flags = opts->flags;
	if (opts->release_agent)
		strcpy(root->release_agent_path, opts->release_agent);
	if (opts->name)
		strcpy(root->name, opts->name);
1555
	if (opts->cpuset_clone_children)
1556
		set_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags);
1557 1558
}

1559
static int cgroup_setup_root(struct cgroup_root *root, unsigned int ss_mask)
1560
{
1561
	LIST_HEAD(tmp_links);
1562
	struct cgroup *root_cgrp = &root->cgrp;
1563 1564
	struct css_set *cset;
	int i, ret;
1565

1566 1567
	lockdep_assert_held(&cgroup_tree_mutex);
	lockdep_assert_held(&cgroup_mutex);
1568

1569
	ret = cgroup_idr_alloc(&root->cgroup_idr, root_cgrp, 1, 2, GFP_NOWAIT);
1570
	if (ret < 0)
T
Tejun Heo 已提交
1571
		goto out;
1572
	root_cgrp->id = ret;
1573

1574
	/*
1575
	 * We're accessing css_set_count without locking css_set_rwsem here,
1576 1577 1578 1579 1580 1581
	 * but that's OK - it can only be increased by someone holding
	 * cgroup_lock, and that's us. The worst that can happen is that we
	 * have some link structures left over
	 */
	ret = allocate_cgrp_cset_links(css_set_count, &tmp_links);
	if (ret)
T
Tejun Heo 已提交
1582
		goto out;
1583

1584
	ret = cgroup_init_root_id(root);
1585
	if (ret)
T
Tejun Heo 已提交
1586
		goto out;
1587

T
Tejun Heo 已提交
1588 1589 1590 1591 1592 1593 1594 1595
	root->kf_root = kernfs_create_root(&cgroup_kf_syscall_ops,
					   KERNFS_ROOT_CREATE_DEACTIVATED,
					   root_cgrp);
	if (IS_ERR(root->kf_root)) {
		ret = PTR_ERR(root->kf_root);
		goto exit_root_id;
	}
	root_cgrp->kn = root->kf_root->kn;
1596

1597 1598
	ret = cgroup_addrm_files(root_cgrp, cgroup_base_files, true);
	if (ret)
T
Tejun Heo 已提交
1599
		goto destroy_root;
1600

1601
	ret = rebind_subsystems(root, ss_mask);
1602
	if (ret)
T
Tejun Heo 已提交
1603
		goto destroy_root;
1604

1605 1606 1607 1608 1609 1610 1611
	/*
	 * There must be no failure case after here, since rebinding takes
	 * care of subsystems' refcounts, which are explicitly dropped in
	 * the failure exit path.
	 */
	list_add(&root->root_list, &cgroup_roots);
	cgroup_root_count++;
A
Al Viro 已提交
1612

1613
	/*
1614
	 * Link the root cgroup in this hierarchy into all the css_set
1615 1616
	 * objects.
	 */
1617
	down_write(&css_set_rwsem);
1618 1619
	hash_for_each(css_set_table, i, cset, hlist)
		link_css_set(&tmp_links, cset, root_cgrp);
1620
	up_write(&css_set_rwsem);
1621

1622
	BUG_ON(!list_empty(&root_cgrp->children));
1623
	BUG_ON(atomic_read(&root->nr_cgrps) != 1);
1624

T
Tejun Heo 已提交
1625
	kernfs_activate(root_cgrp->kn);
1626
	ret = 0;
T
Tejun Heo 已提交
1627
	goto out;
1628

T
Tejun Heo 已提交
1629 1630 1631 1632
destroy_root:
	kernfs_destroy_root(root->kf_root);
	root->kf_root = NULL;
exit_root_id:
1633
	cgroup_exit_root_id(root);
T
Tejun Heo 已提交
1634
out:
1635 1636
	free_cgrp_cset_links(&tmp_links);
	return ret;
1637 1638
}

A
Al Viro 已提交
1639
static struct dentry *cgroup_mount(struct file_system_type *fs_type,
1640
			 int flags, const char *unused_dev_name,
A
Al Viro 已提交
1641
			 void *data)
1642
{
1643
	struct cgroup_root *root;
1644
	struct cgroup_sb_opts opts;
T
Tejun Heo 已提交
1645
	struct dentry *dentry;
1646
	int ret;
L
Li Zefan 已提交
1647
	bool new_sb;
1648

1649 1650 1651 1652 1653 1654
	/*
	 * The first time anyone tries to mount a cgroup, enable the list
	 * linking each css_set to its tasks and fix up all existing tasks.
	 */
	if (!use_task_css_set_links)
		cgroup_enable_task_cg_lists();
1655

1656
	mutex_lock(&cgroup_tree_mutex);
B
Ben Blum 已提交
1657
	mutex_lock(&cgroup_mutex);
1658 1659

	/* First find the desired set of subsystems */
1660
	ret = parse_cgroupfs_options(data, &opts);
1661
	if (ret)
1662
		goto out_unlock;
1663
retry:
T
Tejun Heo 已提交
1664
	/* look for a matching existing root */
T
Tejun Heo 已提交
1665 1666 1667 1668 1669 1670
	if (!opts.subsys_mask && !opts.none && !opts.name) {
		cgrp_dfl_root_visible = true;
		root = &cgrp_dfl_root;
		cgroup_get(&root->cgrp);
		ret = 0;
		goto out_unlock;
1671 1672
	}

1673
	for_each_root(root) {
T
Tejun Heo 已提交
1674
		bool name_match = false;
1675

1676
		if (root == &cgrp_dfl_root)
1677
			continue;
1678

B
Ben Blum 已提交
1679
		/*
T
Tejun Heo 已提交
1680 1681 1682
		 * If we asked for a name then it must match.  Also, if
		 * name matches but sybsys_mask doesn't, we should fail.
		 * Remember whether name matched.
B
Ben Blum 已提交
1683
		 */
T
Tejun Heo 已提交
1684 1685 1686 1687 1688
		if (opts.name) {
			if (strcmp(opts.name, root->name))
				continue;
			name_match = true;
		}
1689

1690
		/*
T
Tejun Heo 已提交
1691 1692
		 * If we asked for subsystems (or explicitly for no
		 * subsystems) then they must match.
1693
		 */
T
Tejun Heo 已提交
1694
		if ((opts.subsys_mask || opts.none) &&
1695
		    (opts.subsys_mask != root->subsys_mask)) {
T
Tejun Heo 已提交
1696 1697 1698 1699 1700
			if (!name_match)
				continue;
			ret = -EBUSY;
			goto out_unlock;
		}
1701

1702
		if ((root->flags ^ opts.flags) & CGRP_ROOT_OPTION_MASK) {
1703
			if ((root->flags | opts.flags) & CGRP_ROOT_SANE_BEHAVIOR) {
1704
				pr_err("sane_behavior: new mount options should match the existing superblock\n");
1705
				ret = -EINVAL;
1706
				goto out_unlock;
1707
			} else {
1708
				pr_warn("new mount options do not match the existing superblock, will be ignored\n");
1709
			}
1710
		}
1711

T
Tejun Heo 已提交
1712
		/*
1713
		 * A root's lifetime is governed by its root cgroup.  Zero
T
Tejun Heo 已提交
1714 1715 1716 1717 1718
		 * ref indicate that the root is being destroyed.  Wait for
		 * destruction to complete so that the subsystems are free.
		 * We can use wait_queue for the wait but this path is
		 * super cold.  Let's just sleep for a bit and retry.
		 */
1719
		if (!atomic_inc_not_zero(&root->cgrp.refcnt)) {
T
Tejun Heo 已提交
1720 1721 1722
			mutex_unlock(&cgroup_mutex);
			mutex_unlock(&cgroup_tree_mutex);
			msleep(10);
1723 1724
			mutex_lock(&cgroup_tree_mutex);
			mutex_lock(&cgroup_mutex);
T
Tejun Heo 已提交
1725 1726
			goto retry;
		}
1727

T
Tejun Heo 已提交
1728
		ret = 0;
T
Tejun Heo 已提交
1729
		goto out_unlock;
1730 1731
	}

1732
	/*
1733 1734 1735
	 * No such thing, create a new one.  name= matching without subsys
	 * specification is allowed for already existing hierarchies but we
	 * can't create new one without subsys specification.
1736
	 */
1737 1738 1739
	if (!opts.subsys_mask && !opts.none) {
		ret = -EINVAL;
		goto out_unlock;
1740 1741
	}

1742 1743 1744
	root = kzalloc(sizeof(*root), GFP_KERNEL);
	if (!root) {
		ret = -ENOMEM;
T
Tejun Heo 已提交
1745
		goto out_unlock;
1746
	}
1747

1748 1749
	init_cgroup_root(root, &opts);

T
Tejun Heo 已提交
1750
	ret = cgroup_setup_root(root, opts.subsys_mask);
T
Tejun Heo 已提交
1751 1752
	if (ret)
		cgroup_free_root(root);
1753

1754
out_unlock:
1755
	mutex_unlock(&cgroup_mutex);
T
Tejun Heo 已提交
1756
	mutex_unlock(&cgroup_tree_mutex);
1757

1758 1759
	kfree(opts.release_agent);
	kfree(opts.name);
A
Aristeu Rozanski 已提交
1760

T
Tejun Heo 已提交
1761
	if (ret)
1762
		return ERR_PTR(ret);
T
Tejun Heo 已提交
1763

L
Li Zefan 已提交
1764 1765
	dentry = kernfs_mount(fs_type, flags, root->kf_root, &new_sb);
	if (IS_ERR(dentry) || !new_sb)
1766
		cgroup_put(&root->cgrp);
T
Tejun Heo 已提交
1767 1768 1769 1770 1771 1772
	return dentry;
}

static void cgroup_kill_sb(struct super_block *sb)
{
	struct kernfs_root *kf_root = kernfs_root_from_sb(sb);
1773
	struct cgroup_root *root = cgroup_root_from_kf(kf_root);
T
Tejun Heo 已提交
1774

1775
	cgroup_put(&root->cgrp);
T
Tejun Heo 已提交
1776
	kernfs_kill_sb(sb);
1777 1778 1779 1780
}

static struct file_system_type cgroup_fs_type = {
	.name = "cgroup",
A
Al Viro 已提交
1781
	.mount = cgroup_mount,
1782 1783 1784
	.kill_sb = cgroup_kill_sb,
};

1785 1786
static struct kobject *cgroup_kobj;

1787
/**
1788
 * task_cgroup_path - cgroup path of a task in the first cgroup hierarchy
1789 1790 1791 1792
 * @task: target task
 * @buf: the buffer to write the path into
 * @buflen: the length of the buffer
 *
1793 1794 1795 1796 1797
 * Determine @task's cgroup on the first (the one with the lowest non-zero
 * hierarchy_id) cgroup hierarchy and copy its path into @buf.  This
 * function grabs cgroup_mutex and shouldn't be used inside locks used by
 * cgroup controller callbacks.
 *
T
Tejun Heo 已提交
1798
 * Return value is the same as kernfs_path().
1799
 */
T
Tejun Heo 已提交
1800
char *task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
1801
{
1802
	struct cgroup_root *root;
1803
	struct cgroup *cgrp;
T
Tejun Heo 已提交
1804 1805
	int hierarchy_id = 1;
	char *path = NULL;
1806 1807

	mutex_lock(&cgroup_mutex);
1808
	down_read(&css_set_rwsem);
1809

1810 1811
	root = idr_get_next(&cgroup_hierarchy_idr, &hierarchy_id);

1812 1813
	if (root) {
		cgrp = task_cgroup_from_root(task, root);
T
Tejun Heo 已提交
1814
		path = cgroup_path(cgrp, buf, buflen);
1815 1816
	} else {
		/* if no hierarchy exists, everyone is in "/" */
T
Tejun Heo 已提交
1817 1818
		if (strlcpy(buf, "/", buflen) < buflen)
			path = buf;
1819 1820
	}

1821
	up_read(&css_set_rwsem);
1822
	mutex_unlock(&cgroup_mutex);
T
Tejun Heo 已提交
1823
	return path;
1824
}
1825
EXPORT_SYMBOL_GPL(task_cgroup_path);
1826

1827
/* used to track tasks and other necessary states during migration */
1828
struct cgroup_taskset {
1829 1830 1831 1832 1833 1834 1835 1836 1837 1838 1839 1840 1841 1842 1843 1844 1845 1846
	/* the src and dst cset list running through cset->mg_node */
	struct list_head	src_csets;
	struct list_head	dst_csets;

	/*
	 * Fields for cgroup_taskset_*() iteration.
	 *
	 * Before migration is committed, the target migration tasks are on
	 * ->mg_tasks of the csets on ->src_csets.  After, on ->mg_tasks of
	 * the csets on ->dst_csets.  ->csets point to either ->src_csets
	 * or ->dst_csets depending on whether migration is committed.
	 *
	 * ->cur_csets and ->cur_task point to the current task position
	 * during iteration.
	 */
	struct list_head	*csets;
	struct css_set		*cur_cset;
	struct task_struct	*cur_task;
1847 1848 1849 1850 1851 1852 1853 1854 1855 1856
};

/**
 * cgroup_taskset_first - reset taskset and return the first task
 * @tset: taskset of interest
 *
 * @tset iteration is initialized and the first task is returned.
 */
struct task_struct *cgroup_taskset_first(struct cgroup_taskset *tset)
{
1857 1858 1859 1860
	tset->cur_cset = list_first_entry(tset->csets, struct css_set, mg_node);
	tset->cur_task = NULL;

	return cgroup_taskset_next(tset);
1861 1862 1863 1864 1865 1866 1867 1868 1869 1870 1871
}

/**
 * cgroup_taskset_next - iterate to the next task in taskset
 * @tset: taskset of interest
 *
 * Return the next task in @tset.  Iteration must have been initialized
 * with cgroup_taskset_first().
 */
struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset)
{
1872 1873
	struct css_set *cset = tset->cur_cset;
	struct task_struct *task = tset->cur_task;
1874

1875 1876 1877 1878 1879 1880
	while (&cset->mg_node != tset->csets) {
		if (!task)
			task = list_first_entry(&cset->mg_tasks,
						struct task_struct, cg_list);
		else
			task = list_next_entry(task, cg_list);
1881

1882 1883 1884 1885 1886
		if (&task->cg_list != &cset->mg_tasks) {
			tset->cur_cset = cset;
			tset->cur_task = task;
			return task;
		}
1887

1888 1889 1890
		cset = list_next_entry(cset, mg_node);
		task = NULL;
	}
1891

1892
	return NULL;
1893 1894
}

1895
/**
B
Ben Blum 已提交
1896
 * cgroup_task_migrate - move a task from one cgroup to another.
1897 1898 1899
 * @old_cgrp; the cgroup @tsk is being migrated from
 * @tsk: the task being migrated
 * @new_cset: the new css_set @tsk is being attached to
B
Ben Blum 已提交
1900
 *
1901
 * Must be called with cgroup_mutex, threadgroup and css_set_rwsem locked.
B
Ben Blum 已提交
1902
 */
1903 1904 1905
static void cgroup_task_migrate(struct cgroup *old_cgrp,
				struct task_struct *tsk,
				struct css_set *new_cset)
B
Ben Blum 已提交
1906
{
1907
	struct css_set *old_cset;
B
Ben Blum 已提交
1908

1909 1910 1911
	lockdep_assert_held(&cgroup_mutex);
	lockdep_assert_held(&css_set_rwsem);

B
Ben Blum 已提交
1912
	/*
1913 1914 1915
	 * We are synchronized through threadgroup_lock() against PF_EXITING
	 * setting such that we can't race against cgroup_exit() changing the
	 * css_set to init_css_set and dropping the old one.
B
Ben Blum 已提交
1916
	 */
1917
	WARN_ON_ONCE(tsk->flags & PF_EXITING);
1918
	old_cset = task_css_set(tsk);
B
Ben Blum 已提交
1919

1920
	get_css_set(new_cset);
1921
	rcu_assign_pointer(tsk->cgroups, new_cset);
B
Ben Blum 已提交
1922

1923 1924 1925 1926 1927 1928 1929
	/*
	 * Use move_tail so that cgroup_taskset_first() still returns the
	 * leader after migration.  This works because cgroup_migrate()
	 * ensures that the dst_cset of the leader is the first on the
	 * tset's dst_csets list.
	 */
	list_move_tail(&tsk->cg_list, &new_cset->mg_tasks);
B
Ben Blum 已提交
1930 1931

	/*
1932 1933 1934
	 * We just gained a reference on old_cset by taking it from the
	 * task. As trading it for new_cset is protected by cgroup_mutex,
	 * we're safe to drop it here; it will be freed under RCU.
B
Ben Blum 已提交
1935
	 */
1936
	set_bit(CGRP_RELEASABLE, &old_cgrp->flags);
1937
	put_css_set_locked(old_cset, false);
B
Ben Blum 已提交
1938 1939
}

L
Li Zefan 已提交
1940
/**
1941 1942
 * cgroup_migrate_finish - cleanup after attach
 * @preloaded_csets: list of preloaded css_sets
B
Ben Blum 已提交
1943
 *
1944 1945
 * Undo cgroup_migrate_add_src() and cgroup_migrate_prepare_dst().  See
 * those functions for details.
B
Ben Blum 已提交
1946
 */
1947
static void cgroup_migrate_finish(struct list_head *preloaded_csets)
B
Ben Blum 已提交
1948
{
1949
	struct css_set *cset, *tmp_cset;
B
Ben Blum 已提交
1950

1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002
	lockdep_assert_held(&cgroup_mutex);

	down_write(&css_set_rwsem);
	list_for_each_entry_safe(cset, tmp_cset, preloaded_csets, mg_preload_node) {
		cset->mg_src_cgrp = NULL;
		cset->mg_dst_cset = NULL;
		list_del_init(&cset->mg_preload_node);
		put_css_set_locked(cset, false);
	}
	up_write(&css_set_rwsem);
}

/**
 * cgroup_migrate_add_src - add a migration source css_set
 * @src_cset: the source css_set to add
 * @dst_cgrp: the destination cgroup
 * @preloaded_csets: list of preloaded css_sets
 *
 * Tasks belonging to @src_cset are about to be migrated to @dst_cgrp.  Pin
 * @src_cset and add it to @preloaded_csets, which should later be cleaned
 * up by cgroup_migrate_finish().
 *
 * This function may be called without holding threadgroup_lock even if the
 * target is a process.  Threads may be created and destroyed but as long
 * as cgroup_mutex is not dropped, no new css_set can be put into play and
 * the preloaded css_sets are guaranteed to cover all migrations.
 */
static void cgroup_migrate_add_src(struct css_set *src_cset,
				   struct cgroup *dst_cgrp,
				   struct list_head *preloaded_csets)
{
	struct cgroup *src_cgrp;

	lockdep_assert_held(&cgroup_mutex);
	lockdep_assert_held(&css_set_rwsem);

	src_cgrp = cset_cgroup_from_root(src_cset, dst_cgrp->root);

	if (!list_empty(&src_cset->mg_preload_node))
		return;

	WARN_ON(src_cset->mg_src_cgrp);
	WARN_ON(!list_empty(&src_cset->mg_tasks));
	WARN_ON(!list_empty(&src_cset->mg_node));

	src_cset->mg_src_cgrp = src_cgrp;
	get_css_set(src_cset);
	list_add(&src_cset->mg_preload_node, preloaded_csets);
}

/**
 * cgroup_migrate_prepare_dst - prepare destination css_sets for migration
2003
 * @dst_cgrp: the destination cgroup (may be %NULL)
2004 2005 2006 2007
 * @preloaded_csets: list of preloaded source css_sets
 *
 * Tasks are about to be moved to @dst_cgrp and all the source css_sets
 * have been preloaded to @preloaded_csets.  This function looks up and
2008 2009 2010
 * pins all destination css_sets, links each to its source, and append them
 * to @preloaded_csets.  If @dst_cgrp is %NULL, the destination of each
 * source css_set is assumed to be its cgroup on the default hierarchy.
2011 2012 2013 2014 2015 2016 2017 2018 2019 2020
 *
 * This function must be called after cgroup_migrate_add_src() has been
 * called on each migration source css_set.  After migration is performed
 * using cgroup_migrate(), cgroup_migrate_finish() must be called on
 * @preloaded_csets.
 */
static int cgroup_migrate_prepare_dst(struct cgroup *dst_cgrp,
				      struct list_head *preloaded_csets)
{
	LIST_HEAD(csets);
2021
	struct css_set *src_cset, *tmp_cset;
2022 2023 2024

	lockdep_assert_held(&cgroup_mutex);

2025 2026 2027 2028 2029 2030 2031 2032
	/*
	 * Except for the root, child_subsys_mask must be zero for a cgroup
	 * with tasks so that child cgroups don't compete against tasks.
	 */
	if (dst_cgrp && cgroup_on_dfl(dst_cgrp) && dst_cgrp->parent &&
	    dst_cgrp->child_subsys_mask)
		return -EBUSY;

2033
	/* look up the dst cset for each src cset and link it to src */
2034
	list_for_each_entry_safe(src_cset, tmp_cset, preloaded_csets, mg_preload_node) {
2035 2036
		struct css_set *dst_cset;

2037 2038
		dst_cset = find_css_set(src_cset,
					dst_cgrp ?: src_cset->dfl_cgrp);
2039 2040 2041 2042
		if (!dst_cset)
			goto err;

		WARN_ON_ONCE(src_cset->mg_dst_cset || dst_cset->mg_dst_cset);
2043 2044 2045 2046 2047 2048 2049 2050 2051 2052 2053 2054 2055 2056

		/*
		 * If src cset equals dst, it's noop.  Drop the src.
		 * cgroup_migrate() will skip the cset too.  Note that we
		 * can't handle src == dst as some nodes are used by both.
		 */
		if (src_cset == dst_cset) {
			src_cset->mg_src_cgrp = NULL;
			list_del_init(&src_cset->mg_preload_node);
			put_css_set(src_cset, false);
			put_css_set(dst_cset, false);
			continue;
		}

2057 2058 2059 2060 2061 2062 2063 2064
		src_cset->mg_dst_cset = dst_cset;

		if (list_empty(&dst_cset->mg_preload_node))
			list_add(&dst_cset->mg_preload_node, &csets);
		else
			put_css_set(dst_cset, false);
	}

2065
	list_splice_tail(&csets, preloaded_csets);
2066 2067 2068 2069 2070 2071 2072 2073 2074 2075 2076 2077 2078 2079 2080 2081 2082 2083 2084 2085 2086 2087 2088 2089 2090 2091
	return 0;
err:
	cgroup_migrate_finish(&csets);
	return -ENOMEM;
}

/**
 * cgroup_migrate - migrate a process or task to a cgroup
 * @cgrp: the destination cgroup
 * @leader: the leader of the process or the task to migrate
 * @threadgroup: whether @leader points to the whole process or a single task
 *
 * Migrate a process or task denoted by @leader to @cgrp.  If migrating a
 * process, the caller must be holding threadgroup_lock of @leader.  The
 * caller is also responsible for invoking cgroup_migrate_add_src() and
 * cgroup_migrate_prepare_dst() on the targets before invoking this
 * function and following up with cgroup_migrate_finish().
 *
 * As long as a controller's ->can_attach() doesn't fail, this function is
 * guaranteed to succeed.  This means that, excluding ->can_attach()
 * failure, when migrating multiple targets, the success or failure can be
 * decided for all targets by invoking group_migrate_prepare_dst() before
 * actually starting migrating.
 */
static int cgroup_migrate(struct cgroup *cgrp, struct task_struct *leader,
			  bool threadgroup)
B
Ben Blum 已提交
2092
{
2093 2094 2095 2096 2097
	struct cgroup_taskset tset = {
		.src_csets	= LIST_HEAD_INIT(tset.src_csets),
		.dst_csets	= LIST_HEAD_INIT(tset.dst_csets),
		.csets		= &tset.src_csets,
	};
T
Tejun Heo 已提交
2098
	struct cgroup_subsys_state *css, *failed_css = NULL;
2099 2100 2101
	struct css_set *cset, *tmp_cset;
	struct task_struct *task, *tmp_task;
	int i, ret;
B
Ben Blum 已提交
2102

2103 2104 2105 2106 2107
	/*
	 * Prevent freeing of tasks while we take a snapshot. Tasks that are
	 * already PF_EXITING could be freed from underneath us unless we
	 * take an rcu_read_lock.
	 */
2108
	down_write(&css_set_rwsem);
2109
	rcu_read_lock();
2110
	task = leader;
B
Ben Blum 已提交
2111
	do {
2112 2113
		/* @task either already exited or can't exit until the end */
		if (task->flags & PF_EXITING)
2114
			goto next;
2115

2116 2117
		/* leave @task alone if post_fork() hasn't linked it yet */
		if (list_empty(&task->cg_list))
2118
			goto next;
2119

2120
		cset = task_css_set(task);
2121
		if (!cset->mg_src_cgrp)
2122
			goto next;
2123

2124
		/*
2125 2126
		 * cgroup_taskset_first() must always return the leader.
		 * Take care to avoid disturbing the ordering.
2127
		 */
2128 2129 2130 2131 2132 2133
		list_move_tail(&task->cg_list, &cset->mg_tasks);
		if (list_empty(&cset->mg_node))
			list_add_tail(&cset->mg_node, &tset.src_csets);
		if (list_empty(&cset->mg_dst_cset->mg_node))
			list_move_tail(&cset->mg_dst_cset->mg_node,
				       &tset.dst_csets);
2134
	next:
2135 2136
		if (!threadgroup)
			break;
2137
	} while_each_thread(leader, task);
2138
	rcu_read_unlock();
2139
	up_write(&css_set_rwsem);
B
Ben Blum 已提交
2140

2141
	/* methods shouldn't be called if no task is actually migrating */
2142 2143
	if (list_empty(&tset.src_csets))
		return 0;
2144

2145
	/* check that we can legitimately attach to the cgroup */
2146
	for_each_e_css(css, i, cgrp) {
T
Tejun Heo 已提交
2147
		if (css->ss->can_attach) {
2148 2149
			ret = css->ss->can_attach(css, &tset);
			if (ret) {
T
Tejun Heo 已提交
2150
				failed_css = css;
B
Ben Blum 已提交
2151 2152 2153 2154 2155 2156
				goto out_cancel_attach;
			}
		}
	}

	/*
2157 2158 2159
	 * Now that we're guaranteed success, proceed to move all tasks to
	 * the new cgroup.  There are no failure cases after here, so this
	 * is the commit point.
B
Ben Blum 已提交
2160
	 */
2161
	down_write(&css_set_rwsem);
2162 2163 2164 2165
	list_for_each_entry(cset, &tset.src_csets, mg_node) {
		list_for_each_entry_safe(task, tmp_task, &cset->mg_tasks, cg_list)
			cgroup_task_migrate(cset->mg_src_cgrp, task,
					    cset->mg_dst_cset);
B
Ben Blum 已提交
2166
	}
2167
	up_write(&css_set_rwsem);
B
Ben Blum 已提交
2168 2169

	/*
2170 2171 2172
	 * Migration is committed, all target tasks are now on dst_csets.
	 * Nothing is sensitive to fork() after this point.  Notify
	 * controllers that migration is complete.
B
Ben Blum 已提交
2173
	 */
2174
	tset.csets = &tset.dst_csets;
B
Ben Blum 已提交
2175

2176
	for_each_e_css(css, i, cgrp)
T
Tejun Heo 已提交
2177 2178
		if (css->ss->attach)
			css->ss->attach(css, &tset);
B
Ben Blum 已提交
2179

2180
	ret = 0;
2181 2182
	goto out_release_tset;

B
Ben Blum 已提交
2183
out_cancel_attach:
2184
	for_each_e_css(css, i, cgrp) {
2185 2186 2187 2188
		if (css == failed_css)
			break;
		if (css->ss->cancel_attach)
			css->ss->cancel_attach(css, &tset);
B
Ben Blum 已提交
2189
	}
2190 2191 2192 2193
out_release_tset:
	down_write(&css_set_rwsem);
	list_splice_init(&tset.dst_csets, &tset.src_csets);
	list_for_each_entry_safe(cset, tmp_cset, &tset.src_csets, mg_node) {
2194
		list_splice_tail_init(&cset->mg_tasks, &cset->tasks);
2195 2196 2197
		list_del_init(&cset->mg_node);
	}
	up_write(&css_set_rwsem);
2198
	return ret;
B
Ben Blum 已提交
2199 2200
}

2201 2202 2203 2204 2205 2206
/**
 * cgroup_attach_task - attach a task or a whole threadgroup to a cgroup
 * @dst_cgrp: the cgroup to attach to
 * @leader: the task or the leader of the threadgroup to be attached
 * @threadgroup: attach the whole threadgroup?
 *
2207
 * Call holding cgroup_mutex and threadgroup_lock of @leader.
2208 2209 2210 2211 2212 2213 2214 2215 2216 2217 2218 2219 2220 2221 2222 2223 2224 2225 2226 2227 2228 2229 2230 2231 2232 2233 2234 2235
 */
static int cgroup_attach_task(struct cgroup *dst_cgrp,
			      struct task_struct *leader, bool threadgroup)
{
	LIST_HEAD(preloaded_csets);
	struct task_struct *task;
	int ret;

	/* look up all src csets */
	down_read(&css_set_rwsem);
	rcu_read_lock();
	task = leader;
	do {
		cgroup_migrate_add_src(task_css_set(task), dst_cgrp,
				       &preloaded_csets);
		if (!threadgroup)
			break;
	} while_each_thread(leader, task);
	rcu_read_unlock();
	up_read(&css_set_rwsem);

	/* prepare dst csets and commit */
	ret = cgroup_migrate_prepare_dst(dst_cgrp, &preloaded_csets);
	if (!ret)
		ret = cgroup_migrate(dst_cgrp, leader, threadgroup);

	cgroup_migrate_finish(&preloaded_csets);
	return ret;
B
Ben Blum 已提交
2236 2237 2238 2239
}

/*
 * Find the task_struct of the task to attach by vpid and pass it along to the
2240
 * function to attach either it or all tasks in its threadgroup. Will lock
2241
 * cgroup_mutex and threadgroup.
2242
 */
B
Ben Blum 已提交
2243
static int attach_task_by_pid(struct cgroup *cgrp, u64 pid, bool threadgroup)
2244 2245
{
	struct task_struct *tsk;
2246
	const struct cred *cred = current_cred(), *tcred;
2247 2248
	int ret;

B
Ben Blum 已提交
2249 2250 2251
	if (!cgroup_lock_live_group(cgrp))
		return -ENODEV;

2252 2253
retry_find_task:
	rcu_read_lock();
2254
	if (pid) {
2255
		tsk = find_task_by_vpid(pid);
B
Ben Blum 已提交
2256 2257
		if (!tsk) {
			rcu_read_unlock();
S
SeongJae Park 已提交
2258
			ret = -ESRCH;
2259
			goto out_unlock_cgroup;
2260
		}
B
Ben Blum 已提交
2261 2262 2263 2264
		/*
		 * even if we're attaching all tasks in the thread group, we
		 * only need to check permissions on one of them.
		 */
2265
		tcred = __task_cred(tsk);
2266 2267 2268
		if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) &&
		    !uid_eq(cred->euid, tcred->uid) &&
		    !uid_eq(cred->euid, tcred->suid)) {
2269
			rcu_read_unlock();
2270 2271
			ret = -EACCES;
			goto out_unlock_cgroup;
2272
		}
2273 2274
	} else
		tsk = current;
2275 2276

	if (threadgroup)
2277
		tsk = tsk->group_leader;
2278 2279

	/*
2280
	 * Workqueue threads may acquire PF_NO_SETAFFINITY and become
2281 2282 2283
	 * trapped in a cpuset, or RT worker may be born in a cgroup
	 * with no rt_runtime allocated.  Just say no.
	 */
2284
	if (tsk == kthreadd_task || (tsk->flags & PF_NO_SETAFFINITY)) {
2285 2286 2287 2288 2289
		ret = -EINVAL;
		rcu_read_unlock();
		goto out_unlock_cgroup;
	}

2290 2291 2292 2293 2294 2295 2296 2297 2298 2299 2300 2301 2302 2303 2304 2305 2306
	get_task_struct(tsk);
	rcu_read_unlock();

	threadgroup_lock(tsk);
	if (threadgroup) {
		if (!thread_group_leader(tsk)) {
			/*
			 * a race with de_thread from another thread's exec()
			 * may strip us of our leadership, if this happens,
			 * there is no choice but to throw this task away and
			 * try again; this is
			 * "double-double-toil-and-trouble-check locking".
			 */
			threadgroup_unlock(tsk);
			put_task_struct(tsk);
			goto retry_find_task;
		}
2307 2308 2309 2310
	}

	ret = cgroup_attach_task(cgrp, tsk, threadgroup);

2311 2312
	threadgroup_unlock(tsk);

2313
	put_task_struct(tsk);
2314
out_unlock_cgroup:
T
Tejun Heo 已提交
2315
	mutex_unlock(&cgroup_mutex);
2316 2317 2318
	return ret;
}

2319 2320 2321 2322 2323 2324 2325
/**
 * cgroup_attach_task_all - attach task 'tsk' to all cgroups of task 'from'
 * @from: attach to all cgroups of a given task
 * @tsk: the task to be attached
 */
int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
{
2326
	struct cgroup_root *root;
2327 2328
	int retval = 0;

T
Tejun Heo 已提交
2329
	mutex_lock(&cgroup_mutex);
2330
	for_each_root(root) {
2331 2332
		struct cgroup *from_cgrp;

2333
		if (root == &cgrp_dfl_root)
2334 2335
			continue;

2336 2337 2338
		down_read(&css_set_rwsem);
		from_cgrp = task_cgroup_from_root(from, root);
		up_read(&css_set_rwsem);
2339

L
Li Zefan 已提交
2340
		retval = cgroup_attach_task(from_cgrp, tsk, false);
2341 2342 2343
		if (retval)
			break;
	}
T
Tejun Heo 已提交
2344
	mutex_unlock(&cgroup_mutex);
2345 2346 2347 2348 2349

	return retval;
}
EXPORT_SYMBOL_GPL(cgroup_attach_task_all);

2350 2351
static int cgroup_tasks_write(struct cgroup_subsys_state *css,
			      struct cftype *cft, u64 pid)
B
Ben Blum 已提交
2352
{
2353
	return attach_task_by_pid(css->cgroup, pid, false);
B
Ben Blum 已提交
2354 2355
}

2356 2357
static int cgroup_procs_write(struct cgroup_subsys_state *css,
			      struct cftype *cft, u64 tgid)
2358
{
2359
	return attach_task_by_pid(css->cgroup, tgid, true);
2360 2361
}

2362
static int cgroup_release_agent_write(struct cgroup_subsys_state *css,
2363
				      struct cftype *cft, char *buffer)
2364
{
2365
	struct cgroup_root *root = css->cgroup->root;
2366 2367

	BUILD_BUG_ON(sizeof(root->release_agent_path) < PATH_MAX);
2368
	if (!cgroup_lock_live_group(css->cgroup))
2369
		return -ENODEV;
2370
	spin_lock(&release_agent_path_lock);
2371 2372
	strlcpy(root->release_agent_path, buffer,
		sizeof(root->release_agent_path));
2373
	spin_unlock(&release_agent_path_lock);
T
Tejun Heo 已提交
2374
	mutex_unlock(&cgroup_mutex);
2375 2376 2377
	return 0;
}

2378
static int cgroup_release_agent_show(struct seq_file *seq, void *v)
2379
{
2380
	struct cgroup *cgrp = seq_css(seq)->cgroup;
2381

2382 2383 2384 2385
	if (!cgroup_lock_live_group(cgrp))
		return -ENODEV;
	seq_puts(seq, cgrp->root->release_agent_path);
	seq_putc(seq, '\n');
T
Tejun Heo 已提交
2386
	mutex_unlock(&cgroup_mutex);
2387 2388 2389
	return 0;
}

2390
static int cgroup_sane_behavior_show(struct seq_file *seq, void *v)
2391
{
2392 2393 2394
	struct cgroup *cgrp = seq_css(seq)->cgroup;

	seq_printf(seq, "%d\n", cgroup_sane_behavior(cgrp));
2395 2396 2397
	return 0;
}

2398 2399 2400 2401 2402 2403 2404 2405 2406 2407 2408 2409 2410 2411 2412 2413 2414 2415 2416 2417 2418 2419 2420 2421 2422 2423 2424 2425 2426 2427 2428 2429 2430 2431 2432 2433 2434 2435 2436 2437 2438 2439 2440 2441 2442 2443 2444 2445 2446 2447 2448 2449 2450 2451 2452 2453 2454 2455 2456 2457 2458 2459 2460 2461 2462 2463 2464 2465 2466 2467 2468 2469 2470 2471 2472 2473 2474 2475 2476 2477 2478 2479 2480 2481 2482 2483 2484 2485 2486 2487 2488 2489 2490 2491 2492 2493 2494 2495 2496 2497 2498 2499 2500 2501 2502 2503 2504 2505 2506 2507 2508 2509 2510 2511 2512 2513 2514 2515 2516 2517 2518 2519 2520 2521 2522 2523 2524 2525 2526 2527 2528 2529 2530 2531 2532 2533 2534 2535 2536 2537 2538 2539 2540 2541 2542 2543
static void cgroup_print_ss_mask(struct seq_file *seq, unsigned int ss_mask)
{
	struct cgroup_subsys *ss;
	bool printed = false;
	int ssid;

	for_each_subsys(ss, ssid) {
		if (ss_mask & (1 << ssid)) {
			if (printed)
				seq_putc(seq, ' ');
			seq_printf(seq, "%s", ss->name);
			printed = true;
		}
	}
	if (printed)
		seq_putc(seq, '\n');
}

/* show controllers which are currently attached to the default hierarchy */
static int cgroup_root_controllers_show(struct seq_file *seq, void *v)
{
	struct cgroup *cgrp = seq_css(seq)->cgroup;

	cgroup_print_ss_mask(seq, cgrp->root->subsys_mask);
	return 0;
}

/* show controllers which are enabled from the parent */
static int cgroup_controllers_show(struct seq_file *seq, void *v)
{
	struct cgroup *cgrp = seq_css(seq)->cgroup;

	cgroup_print_ss_mask(seq, cgrp->parent->child_subsys_mask);
	return 0;
}

/* show controllers which are enabled for a given cgroup's children */
static int cgroup_subtree_control_show(struct seq_file *seq, void *v)
{
	struct cgroup *cgrp = seq_css(seq)->cgroup;

	cgroup_print_ss_mask(seq, cgrp->child_subsys_mask);
	return 0;
}

/**
 * cgroup_update_dfl_csses - update css assoc of a subtree in default hierarchy
 * @cgrp: root of the subtree to update csses for
 *
 * @cgrp's child_subsys_mask has changed and its subtree's (self excluded)
 * css associations need to be updated accordingly.  This function looks up
 * all css_sets which are attached to the subtree, creates the matching
 * updated css_sets and migrates the tasks to the new ones.
 */
static int cgroup_update_dfl_csses(struct cgroup *cgrp)
{
	LIST_HEAD(preloaded_csets);
	struct cgroup_subsys_state *css;
	struct css_set *src_cset;
	int ret;

	lockdep_assert_held(&cgroup_tree_mutex);
	lockdep_assert_held(&cgroup_mutex);

	/* look up all csses currently attached to @cgrp's subtree */
	down_read(&css_set_rwsem);
	css_for_each_descendant_pre(css, cgroup_css(cgrp, NULL)) {
		struct cgrp_cset_link *link;

		/* self is not affected by child_subsys_mask change */
		if (css->cgroup == cgrp)
			continue;

		list_for_each_entry(link, &css->cgroup->cset_links, cset_link)
			cgroup_migrate_add_src(link->cset, cgrp,
					       &preloaded_csets);
	}
	up_read(&css_set_rwsem);

	/* NULL dst indicates self on default hierarchy */
	ret = cgroup_migrate_prepare_dst(NULL, &preloaded_csets);
	if (ret)
		goto out_finish;

	list_for_each_entry(src_cset, &preloaded_csets, mg_preload_node) {
		struct task_struct *last_task = NULL, *task;

		/* src_csets precede dst_csets, break on the first dst_cset */
		if (!src_cset->mg_src_cgrp)
			break;

		/*
		 * All tasks in src_cset need to be migrated to the
		 * matching dst_cset.  Empty it process by process.  We
		 * walk tasks but migrate processes.  The leader might even
		 * belong to a different cset but such src_cset would also
		 * be among the target src_csets because the default
		 * hierarchy enforces per-process membership.
		 */
		while (true) {
			down_read(&css_set_rwsem);
			task = list_first_entry_or_null(&src_cset->tasks,
						struct task_struct, cg_list);
			if (task) {
				task = task->group_leader;
				WARN_ON_ONCE(!task_css_set(task)->mg_src_cgrp);
				get_task_struct(task);
			}
			up_read(&css_set_rwsem);

			if (!task)
				break;

			/* guard against possible infinite loop */
			if (WARN(last_task == task,
				 "cgroup: update_dfl_csses failed to make progress, aborting in inconsistent state\n"))
				goto out_finish;
			last_task = task;

			threadgroup_lock(task);
			/* raced against de_thread() from another thread? */
			if (!thread_group_leader(task)) {
				threadgroup_unlock(task);
				put_task_struct(task);
				continue;
			}

			ret = cgroup_migrate(src_cset->dfl_cgrp, task, true);

			threadgroup_unlock(task);
			put_task_struct(task);

			if (WARN(ret, "cgroup: failed to update controllers for the default hierarchy (%d), further operations may crash or hang\n", ret))
				goto out_finish;
		}
	}

out_finish:
	cgroup_migrate_finish(&preloaded_csets);
	return ret;
}

/* change the enabled child controllers for a cgroup in the default hierarchy */
static int cgroup_subtree_control_write(struct cgroup_subsys_state *dummy_css,
					struct cftype *cft, char *buffer)
{
2544
	unsigned int enable_req = 0, disable_req = 0, enable, disable;
2545 2546 2547 2548 2549 2550 2551 2552 2553 2554 2555 2556 2557 2558 2559 2560 2561 2562 2563 2564 2565 2566 2567 2568 2569 2570 2571 2572 2573 2574 2575 2576 2577 2578 2579 2580 2581 2582 2583 2584 2585 2586 2587 2588 2589 2590 2591 2592 2593 2594 2595 2596 2597 2598 2599 2600 2601 2602 2603 2604 2605 2606 2607 2608 2609 2610 2611 2612 2613 2614 2615 2616 2617 2618 2619 2620 2621 2622 2623 2624 2625 2626 2627 2628 2629 2630 2631 2632 2633 2634 2635 2636 2637 2638 2639 2640 2641 2642 2643 2644 2645 2646 2647 2648 2649 2650 2651 2652 2653 2654 2655 2656 2657 2658 2659 2660 2661 2662 2663 2664 2665 2666 2667 2668 2669 2670 2671 2672 2673 2674 2675 2676 2677 2678 2679 2680 2681 2682 2683 2684 2685 2686 2687 2688 2689 2690 2691 2692 2693 2694 2695 2696 2697 2698 2699 2700 2701 2702 2703 2704 2705 2706 2707 2708 2709 2710 2711 2712 2713 2714 2715 2716 2717
	struct cgroup *cgrp = dummy_css->cgroup, *child;
	struct cgroup_subsys *ss;
	char *tok, *p;
	int ssid, ret;

	/*
	 * Parse input - white space separated list of subsystem names
	 * prefixed with either + or -.
	 */
	p = buffer;
	while ((tok = strsep(&p, " \t\n"))) {
		for_each_subsys(ss, ssid) {
			if (ss->disabled || strcmp(tok + 1, ss->name))
				continue;

			if (*tok == '+') {
				enable_req |= 1 << ssid;
				disable_req &= ~(1 << ssid);
			} else if (*tok == '-') {
				disable_req |= 1 << ssid;
				enable_req &= ~(1 << ssid);
			} else {
				return -EINVAL;
			}
			break;
		}
		if (ssid == CGROUP_SUBSYS_COUNT)
			return -EINVAL;
	}

	/*
	 * We're gonna grab cgroup_tree_mutex which nests outside kernfs
	 * active_ref.  cgroup_lock_live_group() already provides enough
	 * protection.  Ensure @cgrp stays accessible and break the
	 * active_ref protection.
	 */
	cgroup_get(cgrp);
	kernfs_break_active_protection(cgrp->control_kn);
retry:
	enable = enable_req;
	disable = disable_req;

	mutex_lock(&cgroup_tree_mutex);

	for_each_subsys(ss, ssid) {
		if (enable & (1 << ssid)) {
			if (cgrp->child_subsys_mask & (1 << ssid)) {
				enable &= ~(1 << ssid);
				continue;
			}

			/*
			 * Because css offlining is asynchronous, userland
			 * might try to re-enable the same controller while
			 * the previous instance is still around.  In such
			 * cases, wait till it's gone using offline_waitq.
			 */
			cgroup_for_each_live_child(child, cgrp) {
				wait_queue_t wait;

				if (!cgroup_css(child, ss))
					continue;

				prepare_to_wait(&child->offline_waitq, &wait,
						TASK_UNINTERRUPTIBLE);
				mutex_unlock(&cgroup_tree_mutex);
				schedule();
				finish_wait(&child->offline_waitq, &wait);
				goto retry;
			}

			/* unavailable or not enabled on the parent? */
			if (!(cgrp_dfl_root.subsys_mask & (1 << ssid)) ||
			    (cgrp->parent &&
			     !(cgrp->parent->child_subsys_mask & (1 << ssid)))) {
				ret = -ENOENT;
				goto out_unlock_tree;
			}
		} else if (disable & (1 << ssid)) {
			if (!(cgrp->child_subsys_mask & (1 << ssid))) {
				disable &= ~(1 << ssid);
				continue;
			}

			/* a child has it enabled? */
			cgroup_for_each_live_child(child, cgrp) {
				if (child->child_subsys_mask & (1 << ssid)) {
					ret = -EBUSY;
					goto out_unlock_tree;
				}
			}
		}
	}

	if (!enable && !disable) {
		ret = 0;
		goto out_unlock_tree;
	}

	if (!cgroup_lock_live_group(cgrp)) {
		ret = -ENODEV;
		goto out_unlock_tree;
	}

	/*
	 * Except for the root, child_subsys_mask must be zero for a cgroup
	 * with tasks so that child cgroups don't compete against tasks.
	 */
	if (enable && cgrp->parent && !list_empty(&cgrp->cset_links)) {
		ret = -EBUSY;
		goto out_unlock;
	}

	/*
	 * Create csses for enables and update child_subsys_mask.  This
	 * changes cgroup_e_css() results which in turn makes the
	 * subsequent cgroup_update_dfl_csses() associate all tasks in the
	 * subtree to the updated csses.
	 */
	for_each_subsys(ss, ssid) {
		if (!(enable & (1 << ssid)))
			continue;

		cgroup_for_each_live_child(child, cgrp) {
			ret = create_css(child, ss);
			if (ret)
				goto err_undo_css;
		}
	}

	cgrp->child_subsys_mask |= enable;
	cgrp->child_subsys_mask &= ~disable;

	ret = cgroup_update_dfl_csses(cgrp);
	if (ret)
		goto err_undo_css;

	/* all tasks are now migrated away from the old csses, kill them */
	for_each_subsys(ss, ssid) {
		if (!(disable & (1 << ssid)))
			continue;

		cgroup_for_each_live_child(child, cgrp)
			kill_css(cgroup_css(child, ss));
	}

	kernfs_activate(cgrp->kn);
	ret = 0;
out_unlock:
	mutex_unlock(&cgroup_mutex);
out_unlock_tree:
	mutex_unlock(&cgroup_tree_mutex);
	kernfs_unbreak_active_protection(cgrp->control_kn);
	cgroup_put(cgrp);
	return ret;

err_undo_css:
	cgrp->child_subsys_mask &= ~enable;
	cgrp->child_subsys_mask |= disable;

	for_each_subsys(ss, ssid) {
		if (!(enable & (1 << ssid)))
			continue;

		cgroup_for_each_live_child(child, cgrp) {
			struct cgroup_subsys_state *css = cgroup_css(child, ss);
			if (css)
				kill_css(css);
		}
	}
	goto out_unlock;
}

2718 2719 2720 2721 2722 2723
static int cgroup_populated_show(struct seq_file *seq, void *v)
{
	seq_printf(seq, "%d\n", (bool)seq_css(seq)->cgroup->populated_cnt);
	return 0;
}

T
Tejun Heo 已提交
2724 2725
static ssize_t cgroup_file_write(struct kernfs_open_file *of, char *buf,
				 size_t nbytes, loff_t off)
2726
{
T
Tejun Heo 已提交
2727 2728 2729
	struct cgroup *cgrp = of->kn->parent->priv;
	struct cftype *cft = of->kn->priv;
	struct cgroup_subsys_state *css;
2730
	int ret;
2731

T
Tejun Heo 已提交
2732 2733 2734 2735 2736 2737 2738 2739 2740
	/*
	 * kernfs guarantees that a file isn't deleted with operations in
	 * flight, which means that the matching css is and stays alive and
	 * doesn't need to be pinned.  The RCU locking is not necessary
	 * either.  It's just for the convenience of using cgroup_css().
	 */
	rcu_read_lock();
	css = cgroup_css(cgrp, cft->ss);
	rcu_read_unlock();
2741 2742 2743 2744 2745 2746 2747 2748 2749 2750 2751 2752 2753 2754 2755

	if (cft->write_string) {
		ret = cft->write_string(css, cft, strstrip(buf));
	} else if (cft->write_u64) {
		unsigned long long v;
		ret = kstrtoull(buf, 0, &v);
		if (!ret)
			ret = cft->write_u64(css, cft, v);
	} else if (cft->write_s64) {
		long long v;
		ret = kstrtoll(buf, 0, &v);
		if (!ret)
			ret = cft->write_s64(css, cft, v);
	} else if (cft->trigger) {
		ret = cft->trigger(css, (unsigned int)cft->private);
2756
	} else {
2757
		ret = -EINVAL;
2758
	}
T
Tejun Heo 已提交
2759

2760
	return ret ?: nbytes;
2761 2762
}

2763
static void *cgroup_seqfile_start(struct seq_file *seq, loff_t *ppos)
2764
{
T
Tejun Heo 已提交
2765
	return seq_cft(seq)->seq_start(seq, ppos);
2766 2767
}

2768
static void *cgroup_seqfile_next(struct seq_file *seq, void *v, loff_t *ppos)
2769
{
T
Tejun Heo 已提交
2770
	return seq_cft(seq)->seq_next(seq, v, ppos);
2771 2772
}

2773
static void cgroup_seqfile_stop(struct seq_file *seq, void *v)
2774
{
T
Tejun Heo 已提交
2775
	seq_cft(seq)->seq_stop(seq, v);
2776 2777
}

2778
static int cgroup_seqfile_show(struct seq_file *m, void *arg)
2779
{
2780 2781
	struct cftype *cft = seq_cft(m);
	struct cgroup_subsys_state *css = seq_css(m);
2782

2783 2784
	if (cft->seq_show)
		return cft->seq_show(m, arg);
2785

2786
	if (cft->read_u64)
2787 2788 2789 2790 2791 2792
		seq_printf(m, "%llu\n", cft->read_u64(css, cft));
	else if (cft->read_s64)
		seq_printf(m, "%lld\n", cft->read_s64(css, cft));
	else
		return -EINVAL;
	return 0;
2793 2794
}

T
Tejun Heo 已提交
2795 2796 2797 2798
static struct kernfs_ops cgroup_kf_single_ops = {
	.atomic_write_len	= PAGE_SIZE,
	.write			= cgroup_file_write,
	.seq_show		= cgroup_seqfile_show,
2799 2800
};

T
Tejun Heo 已提交
2801 2802 2803 2804 2805 2806 2807 2808
static struct kernfs_ops cgroup_kf_ops = {
	.atomic_write_len	= PAGE_SIZE,
	.write			= cgroup_file_write,
	.seq_start		= cgroup_seqfile_start,
	.seq_next		= cgroup_seqfile_next,
	.seq_stop		= cgroup_seqfile_stop,
	.seq_show		= cgroup_seqfile_show,
};
2809 2810 2811 2812

/*
 * cgroup_rename - Only allow simple rename of directories in place.
 */
T
Tejun Heo 已提交
2813 2814
static int cgroup_rename(struct kernfs_node *kn, struct kernfs_node *new_parent,
			 const char *new_name_str)
2815
{
T
Tejun Heo 已提交
2816
	struct cgroup *cgrp = kn->priv;
2817 2818
	int ret;

T
Tejun Heo 已提交
2819
	if (kernfs_type(kn) != KERNFS_DIR)
2820
		return -ENOTDIR;
T
Tejun Heo 已提交
2821
	if (kn->parent != new_parent)
2822
		return -EIO;
2823

2824 2825 2826 2827 2828 2829
	/*
	 * This isn't a proper migration and its usefulness is very
	 * limited.  Disallow if sane_behavior.
	 */
	if (cgroup_sane_behavior(cgrp))
		return -EPERM;
L
Li Zefan 已提交
2830

2831 2832 2833 2834 2835 2836 2837
	/*
	 * We're gonna grab cgroup_tree_mutex which nests outside kernfs
	 * active_ref.  kernfs_rename() doesn't require active_ref
	 * protection.  Break them before grabbing cgroup_tree_mutex.
	 */
	kernfs_break_active_protection(new_parent);
	kernfs_break_active_protection(kn);
L
Li Zefan 已提交
2838

T
Tejun Heo 已提交
2839 2840
	mutex_lock(&cgroup_tree_mutex);
	mutex_lock(&cgroup_mutex);
L
Li Zefan 已提交
2841

T
Tejun Heo 已提交
2842
	ret = kernfs_rename(kn, new_parent, new_name_str);
L
Li Zefan 已提交
2843

T
Tejun Heo 已提交
2844 2845
	mutex_unlock(&cgroup_mutex);
	mutex_unlock(&cgroup_tree_mutex);
2846 2847 2848

	kernfs_unbreak_active_protection(kn);
	kernfs_unbreak_active_protection(new_parent);
T
Tejun Heo 已提交
2849
	return ret;
L
Li Zefan 已提交
2850 2851
}

2852 2853 2854 2855 2856 2857 2858 2859 2860 2861 2862 2863 2864 2865
/* set uid and gid of cgroup dirs and files to that of the creator */
static int cgroup_kn_set_ugid(struct kernfs_node *kn)
{
	struct iattr iattr = { .ia_valid = ATTR_UID | ATTR_GID,
			       .ia_uid = current_fsuid(),
			       .ia_gid = current_fsgid(), };

	if (uid_eq(iattr.ia_uid, GLOBAL_ROOT_UID) &&
	    gid_eq(iattr.ia_gid, GLOBAL_ROOT_GID))
		return 0;

	return kernfs_setattr(kn, &iattr);
}

2866
static int cgroup_add_file(struct cgroup *cgrp, struct cftype *cft)
2867
{
T
Tejun Heo 已提交
2868
	char name[CGROUP_FILE_NAME_MAX];
T
Tejun Heo 已提交
2869 2870
	struct kernfs_node *kn;
	struct lock_class_key *key = NULL;
2871
	int ret;
T
Tejun Heo 已提交
2872

T
Tejun Heo 已提交
2873 2874 2875 2876 2877 2878
#ifdef CONFIG_DEBUG_LOCK_ALLOC
	key = &cft->lockdep_key;
#endif
	kn = __kernfs_create_file(cgrp->kn, cgroup_file_name(cgrp, cft, name),
				  cgroup_file_mode(cft), 0, cft->kf_ops, cft,
				  NULL, false, key);
2879 2880 2881 2882
	if (IS_ERR(kn))
		return PTR_ERR(kn);

	ret = cgroup_kn_set_ugid(kn);
2883
	if (ret) {
2884
		kernfs_remove(kn);
2885 2886 2887 2888 2889
		return ret;
	}

	if (cft->seq_show == cgroup_subtree_control_show)
		cgrp->control_kn = kn;
2890 2891
	else if (cft->seq_show == cgroup_populated_show)
		cgrp->populated_kn = kn;
2892
	return 0;
2893 2894
}

2895 2896 2897 2898 2899 2900 2901
/**
 * cgroup_addrm_files - add or remove files to a cgroup directory
 * @cgrp: the target cgroup
 * @cfts: array of cftypes to be added
 * @is_add: whether to add or remove
 *
 * Depending on @is_add, add or remove files defined by @cfts on @cgrp.
2902 2903 2904
 * For removals, this function never fails.  If addition fails, this
 * function doesn't remove files already added.  The caller is responsible
 * for cleaning up.
2905
 */
2906 2907
static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[],
			      bool is_add)
2908
{
A
Aristeu Rozanski 已提交
2909
	struct cftype *cft;
2910 2911
	int ret;

T
Tejun Heo 已提交
2912
	lockdep_assert_held(&cgroup_tree_mutex);
T
Tejun Heo 已提交
2913 2914

	for (cft = cfts; cft->name[0] != '\0'; cft++) {
2915
		/* does cft->flags tell us to skip this file on @cgrp? */
T
Tejun Heo 已提交
2916 2917
		if ((cft->flags & CFTYPE_ONLY_ON_DFL) && !cgroup_on_dfl(cgrp))
			continue;
2918 2919
		if ((cft->flags & CFTYPE_INSANE) && cgroup_sane_behavior(cgrp))
			continue;
2920 2921 2922 2923 2924
		if ((cft->flags & CFTYPE_NOT_ON_ROOT) && !cgrp->parent)
			continue;
		if ((cft->flags & CFTYPE_ONLY_ON_ROOT) && cgrp->parent)
			continue;

2925
		if (is_add) {
2926
			ret = cgroup_add_file(cgrp, cft);
2927
			if (ret) {
2928 2929
				pr_warn("%s: failed to add %s, err=%d\n",
					__func__, cft->name, ret);
2930 2931
				return ret;
			}
2932 2933
		} else {
			cgroup_rm_file(cgrp, cft);
T
Tejun Heo 已提交
2934
		}
2935
	}
2936
	return 0;
2937 2938
}

2939
static int cgroup_apply_cftypes(struct cftype *cfts, bool is_add)
2940 2941
{
	LIST_HEAD(pending);
2942
	struct cgroup_subsys *ss = cfts[0].ss;
2943
	struct cgroup *root = &ss->root->cgrp;
2944
	struct cgroup_subsys_state *css;
2945
	int ret = 0;
2946

2947
	lockdep_assert_held(&cgroup_tree_mutex);
2948

2949
	/* add/rm files for all cgroups created before */
2950
	css_for_each_descendant_pre(css, cgroup_css(root, ss)) {
2951 2952
		struct cgroup *cgrp = css->cgroup;

2953 2954 2955
		if (cgroup_is_dead(cgrp))
			continue;

2956
		ret = cgroup_addrm_files(cgrp, cfts, is_add);
2957 2958
		if (ret)
			break;
2959
	}
2960 2961 2962

	if (is_add && !ret)
		kernfs_activate(root->kn);
2963
	return ret;
2964 2965
}

2966
static void cgroup_exit_cftypes(struct cftype *cfts)
2967
{
2968
	struct cftype *cft;
2969

T
Tejun Heo 已提交
2970 2971 2972 2973 2974
	for (cft = cfts; cft->name[0] != '\0'; cft++) {
		/* free copy for custom atomic_write_len, see init_cftypes() */
		if (cft->max_write_len && cft->max_write_len != PAGE_SIZE)
			kfree(cft->kf_ops);
		cft->kf_ops = NULL;
2975
		cft->ss = NULL;
T
Tejun Heo 已提交
2976
	}
2977 2978
}

T
Tejun Heo 已提交
2979
static int cgroup_init_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
2980 2981 2982
{
	struct cftype *cft;

T
Tejun Heo 已提交
2983 2984 2985
	for (cft = cfts; cft->name[0] != '\0'; cft++) {
		struct kernfs_ops *kf_ops;

T
Tejun Heo 已提交
2986 2987
		WARN_ON(cft->ss || cft->kf_ops);

T
Tejun Heo 已提交
2988 2989 2990 2991 2992 2993 2994 2995 2996 2997 2998 2999 3000 3001 3002 3003 3004
		if (cft->seq_start)
			kf_ops = &cgroup_kf_ops;
		else
			kf_ops = &cgroup_kf_single_ops;

		/*
		 * Ugh... if @cft wants a custom max_write_len, we need to
		 * make a copy of kf_ops to set its atomic_write_len.
		 */
		if (cft->max_write_len && cft->max_write_len != PAGE_SIZE) {
			kf_ops = kmemdup(kf_ops, sizeof(*kf_ops), GFP_KERNEL);
			if (!kf_ops) {
				cgroup_exit_cftypes(cfts);
				return -ENOMEM;
			}
			kf_ops->atomic_write_len = cft->max_write_len;
		}
3005

T
Tejun Heo 已提交
3006
		cft->kf_ops = kf_ops;
3007
		cft->ss = ss;
T
Tejun Heo 已提交
3008
	}
3009

T
Tejun Heo 已提交
3010
	return 0;
3011 3012
}

3013 3014 3015 3016 3017 3018 3019 3020 3021 3022 3023
static int cgroup_rm_cftypes_locked(struct cftype *cfts)
{
	lockdep_assert_held(&cgroup_tree_mutex);

	if (!cfts || !cfts[0].ss)
		return -ENOENT;

	list_del(&cfts->node);
	cgroup_apply_cftypes(cfts, false);
	cgroup_exit_cftypes(cfts);
	return 0;
3024 3025
}

3026 3027 3028 3029
/**
 * cgroup_rm_cftypes - remove an array of cftypes from a subsystem
 * @cfts: zero-length name terminated array of cftypes
 *
3030 3031 3032
 * Unregister @cfts.  Files described by @cfts are removed from all
 * existing cgroups and all future cgroups won't have them either.  This
 * function can be called anytime whether @cfts' subsys is attached or not.
3033 3034
 *
 * Returns 0 on successful unregistration, -ENOENT if @cfts is not
3035
 * registered.
3036
 */
3037
int cgroup_rm_cftypes(struct cftype *cfts)
3038
{
3039
	int ret;
3040

3041 3042 3043 3044
	mutex_lock(&cgroup_tree_mutex);
	ret = cgroup_rm_cftypes_locked(cfts);
	mutex_unlock(&cgroup_tree_mutex);
	return ret;
T
Tejun Heo 已提交
3045 3046
}

3047 3048 3049 3050 3051 3052 3053 3054 3055 3056 3057 3058 3059 3060
/**
 * cgroup_add_cftypes - add an array of cftypes to a subsystem
 * @ss: target cgroup subsystem
 * @cfts: zero-length name terminated array of cftypes
 *
 * Register @cfts to @ss.  Files described by @cfts are created for all
 * existing cgroups to which @ss is attached and all future cgroups will
 * have them too.  This function can be called anytime whether @ss is
 * attached or not.
 *
 * Returns 0 on successful registration, -errno on failure.  Note that this
 * function currently returns 0 as long as @cfts registration is successful
 * even if some file creation attempts on existing cgroups fail.
 */
A
Aristeu Rozanski 已提交
3061
int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
3062
{
3063
	int ret;
3064

3065 3066
	if (!cfts || cfts[0].name[0] == '\0')
		return 0;
3067

T
Tejun Heo 已提交
3068 3069 3070
	ret = cgroup_init_cftypes(ss, cfts);
	if (ret)
		return ret;
3071

3072 3073
	mutex_lock(&cgroup_tree_mutex);

T
Tejun Heo 已提交
3074
	list_add_tail(&cfts->node, &ss->cfts);
3075
	ret = cgroup_apply_cftypes(cfts, true);
3076
	if (ret)
3077
		cgroup_rm_cftypes_locked(cfts);
3078

3079
	mutex_unlock(&cgroup_tree_mutex);
3080
	return ret;
3081 3082
}

L
Li Zefan 已提交
3083 3084 3085 3086 3087 3088
/**
 * cgroup_task_count - count the number of tasks in a cgroup.
 * @cgrp: the cgroup in question
 *
 * Return the number of tasks in the cgroup.
 */
3089
static int cgroup_task_count(const struct cgroup *cgrp)
3090 3091
{
	int count = 0;
3092
	struct cgrp_cset_link *link;
3093

3094
	down_read(&css_set_rwsem);
3095 3096
	list_for_each_entry(link, &cgrp->cset_links, cset_link)
		count += atomic_read(&link->cset->refcount);
3097
	up_read(&css_set_rwsem);
3098 3099 3100
	return count;
}

3101
/**
3102 3103 3104
 * css_next_child - find the next child of a given css
 * @pos_css: the current position (%NULL to initiate traversal)
 * @parent_css: css whose children to walk
3105
 *
3106
 * This function returns the next child of @parent_css and should be called
3107 3108 3109
 * under either cgroup_mutex or RCU read lock.  The only requirement is
 * that @parent_css and @pos_css are accessible.  The next sibling is
 * guaranteed to be returned regardless of their states.
3110
 */
3111 3112 3113
struct cgroup_subsys_state *
css_next_child(struct cgroup_subsys_state *pos_css,
	       struct cgroup_subsys_state *parent_css)
3114
{
3115 3116
	struct cgroup *pos = pos_css ? pos_css->cgroup : NULL;
	struct cgroup *cgrp = parent_css->cgroup;
3117 3118
	struct cgroup *next;

T
Tejun Heo 已提交
3119
	cgroup_assert_mutexes_or_rcu_locked();
3120 3121 3122 3123

	/*
	 * @pos could already have been removed.  Once a cgroup is removed,
	 * its ->sibling.next is no longer updated when its next sibling
3124 3125 3126 3127 3128 3129 3130
	 * changes.  As CGRP_DEAD assertion is serialized and happens
	 * before the cgroup is taken off the ->sibling list, if we see it
	 * unasserted, it's guaranteed that the next sibling hasn't
	 * finished its grace period even if it's already removed, and thus
	 * safe to dereference from this RCU critical section.  If
	 * ->sibling.next is inaccessible, cgroup_is_dead() is guaranteed
	 * to be visible as %true here.
3131 3132 3133 3134 3135 3136 3137 3138
	 *
	 * If @pos is dead, its next pointer can't be dereferenced;
	 * however, as each cgroup is given a monotonically increasing
	 * unique serial number and always appended to the sibling list,
	 * the next one can be found by walking the parent's children until
	 * we see a cgroup with higher serial number than @pos's.  While
	 * this path can be slower, it's taken only when either the current
	 * cgroup is removed or iteration and removal race.
3139
	 */
3140 3141 3142
	if (!pos) {
		next = list_entry_rcu(cgrp->children.next, struct cgroup, sibling);
	} else if (likely(!cgroup_is_dead(pos))) {
3143
		next = list_entry_rcu(pos->sibling.next, struct cgroup, sibling);
3144 3145 3146 3147
	} else {
		list_for_each_entry_rcu(next, &cgrp->children, sibling)
			if (next->serial_nr > pos->serial_nr)
				break;
3148 3149
	}

3150 3151 3152 3153 3154 3155 3156
	/*
	 * @next, if not pointing to the head, can be dereferenced and is
	 * the next sibling; however, it might have @ss disabled.  If so,
	 * fast-forward to the next enabled one.
	 */
	while (&next->sibling != &cgrp->children) {
		struct cgroup_subsys_state *next_css = cgroup_css(next, parent_css->ss);
3157

3158 3159 3160 3161 3162
		if (next_css)
			return next_css;
		next = list_entry_rcu(next->sibling.next, struct cgroup, sibling);
	}
	return NULL;
3163 3164
}

3165
/**
3166
 * css_next_descendant_pre - find the next descendant for pre-order walk
3167
 * @pos: the current position (%NULL to initiate traversal)
3168
 * @root: css whose descendants to walk
3169
 *
3170
 * To be used by css_for_each_descendant_pre().  Find the next descendant
3171 3172
 * to visit for pre-order traversal of @root's descendants.  @root is
 * included in the iteration and the first node to be visited.
3173
 *
3174 3175 3176 3177
 * While this function requires cgroup_mutex or RCU read locking, it
 * doesn't require the whole traversal to be contained in a single critical
 * section.  This function will return the correct next descendant as long
 * as both @pos and @root are accessible and @pos is a descendant of @root.
3178
 */
3179 3180 3181
struct cgroup_subsys_state *
css_next_descendant_pre(struct cgroup_subsys_state *pos,
			struct cgroup_subsys_state *root)
3182
{
3183
	struct cgroup_subsys_state *next;
3184

T
Tejun Heo 已提交
3185
	cgroup_assert_mutexes_or_rcu_locked();
3186

3187
	/* if first iteration, visit @root */
3188
	if (!pos)
3189
		return root;
3190 3191

	/* visit the first child if exists */
3192
	next = css_next_child(NULL, pos);
3193 3194 3195 3196
	if (next)
		return next;

	/* no child, visit my or the closest ancestor's next sibling */
3197 3198
	while (pos != root) {
		next = css_next_child(pos, css_parent(pos));
3199
		if (next)
3200
			return next;
3201
		pos = css_parent(pos);
3202
	}
3203 3204 3205 3206

	return NULL;
}

3207
/**
3208 3209
 * css_rightmost_descendant - return the rightmost descendant of a css
 * @pos: css of interest
3210
 *
3211 3212
 * Return the rightmost descendant of @pos.  If there's no descendant, @pos
 * is returned.  This can be used during pre-order traversal to skip
3213
 * subtree of @pos.
3214
 *
3215 3216 3217 3218
 * While this function requires cgroup_mutex or RCU read locking, it
 * doesn't require the whole traversal to be contained in a single critical
 * section.  This function will return the correct rightmost descendant as
 * long as @pos is accessible.
3219
 */
3220 3221
struct cgroup_subsys_state *
css_rightmost_descendant(struct cgroup_subsys_state *pos)
3222
{
3223
	struct cgroup_subsys_state *last, *tmp;
3224

T
Tejun Heo 已提交
3225
	cgroup_assert_mutexes_or_rcu_locked();
3226 3227 3228 3229 3230

	do {
		last = pos;
		/* ->prev isn't RCU safe, walk ->next till the end */
		pos = NULL;
3231
		css_for_each_child(tmp, last)
3232 3233 3234 3235 3236 3237
			pos = tmp;
	} while (pos);

	return last;
}

3238 3239
static struct cgroup_subsys_state *
css_leftmost_descendant(struct cgroup_subsys_state *pos)
3240
{
3241
	struct cgroup_subsys_state *last;
3242 3243 3244

	do {
		last = pos;
3245
		pos = css_next_child(NULL, pos);
3246 3247 3248 3249 3250 3251
	} while (pos);

	return last;
}

/**
3252
 * css_next_descendant_post - find the next descendant for post-order walk
3253
 * @pos: the current position (%NULL to initiate traversal)
3254
 * @root: css whose descendants to walk
3255
 *
3256
 * To be used by css_for_each_descendant_post().  Find the next descendant
3257 3258
 * to visit for post-order traversal of @root's descendants.  @root is
 * included in the iteration and the last node to be visited.
3259
 *
3260 3261 3262 3263 3264
 * While this function requires cgroup_mutex or RCU read locking, it
 * doesn't require the whole traversal to be contained in a single critical
 * section.  This function will return the correct next descendant as long
 * as both @pos and @cgroup are accessible and @pos is a descendant of
 * @cgroup.
3265
 */
3266 3267 3268
struct cgroup_subsys_state *
css_next_descendant_post(struct cgroup_subsys_state *pos,
			 struct cgroup_subsys_state *root)
3269
{
3270
	struct cgroup_subsys_state *next;
3271

T
Tejun Heo 已提交
3272
	cgroup_assert_mutexes_or_rcu_locked();
3273

3274 3275 3276
	/* if first iteration, visit leftmost descendant which may be @root */
	if (!pos)
		return css_leftmost_descendant(root);
3277

3278 3279 3280 3281
	/* if we visited @root, we're done */
	if (pos == root)
		return NULL;

3282
	/* if there's an unvisited sibling, visit its leftmost descendant */
3283
	next = css_next_child(pos, css_parent(pos));
3284
	if (next)
3285
		return css_leftmost_descendant(next);
3286 3287

	/* no sibling left, visit parent */
3288
	return css_parent(pos);
3289 3290
}

3291
/**
3292
 * css_advance_task_iter - advance a task itererator to the next css_set
3293 3294 3295
 * @it: the iterator to advance
 *
 * Advance @it to the next css_set to walk.
3296
 */
3297
static void css_advance_task_iter(struct css_task_iter *it)
3298
{
T
Tejun Heo 已提交
3299
	struct list_head *l = it->cset_pos;
3300 3301 3302 3303 3304 3305
	struct cgrp_cset_link *link;
	struct css_set *cset;

	/* Advance to the next non-empty css_set */
	do {
		l = l->next;
T
Tejun Heo 已提交
3306 3307
		if (l == it->cset_head) {
			it->cset_pos = NULL;
3308 3309
			return;
		}
3310 3311 3312 3313 3314 3315 3316 3317

		if (it->ss) {
			cset = container_of(l, struct css_set,
					    e_cset_node[it->ss->id]);
		} else {
			link = list_entry(l, struct cgrp_cset_link, cset_link);
			cset = link->cset;
		}
T
Tejun Heo 已提交
3318 3319
	} while (list_empty(&cset->tasks) && list_empty(&cset->mg_tasks));

T
Tejun Heo 已提交
3320
	it->cset_pos = l;
T
Tejun Heo 已提交
3321 3322

	if (!list_empty(&cset->tasks))
T
Tejun Heo 已提交
3323
		it->task_pos = cset->tasks.next;
T
Tejun Heo 已提交
3324
	else
T
Tejun Heo 已提交
3325 3326 3327 3328
		it->task_pos = cset->mg_tasks.next;

	it->tasks_head = &cset->tasks;
	it->mg_tasks_head = &cset->mg_tasks;
3329 3330
}

3331
/**
3332 3333
 * css_task_iter_start - initiate task iteration
 * @css: the css to walk tasks of
3334 3335
 * @it: the task iterator to use
 *
3336 3337 3338 3339
 * Initiate iteration through the tasks of @css.  The caller can call
 * css_task_iter_next() to walk through the tasks until the function
 * returns NULL.  On completion of iteration, css_task_iter_end() must be
 * called.
3340 3341 3342 3343 3344
 *
 * Note that this function acquires a lock which is released when the
 * iteration finishes.  The caller can't sleep while iteration is in
 * progress.
 */
3345 3346
void css_task_iter_start(struct cgroup_subsys_state *css,
			 struct css_task_iter *it)
3347
	__acquires(css_set_rwsem)
3348
{
3349 3350
	/* no one should try to iterate before mounting cgroups */
	WARN_ON_ONCE(!use_task_css_set_links);
3351

3352
	down_read(&css_set_rwsem);
3353

3354 3355 3356 3357 3358 3359 3360
	it->ss = css->ss;

	if (it->ss)
		it->cset_pos = &css->cgroup->e_csets[css->ss->id];
	else
		it->cset_pos = &css->cgroup->cset_links;

T
Tejun Heo 已提交
3361
	it->cset_head = it->cset_pos;
3362

3363
	css_advance_task_iter(it);
3364 3365
}

3366
/**
3367
 * css_task_iter_next - return the next task for the iterator
3368 3369 3370
 * @it: the task iterator being iterated
 *
 * The "next" function for task iteration.  @it should have been
3371 3372
 * initialized via css_task_iter_start().  Returns NULL when the iteration
 * reaches the end.
3373
 */
3374
struct task_struct *css_task_iter_next(struct css_task_iter *it)
3375 3376
{
	struct task_struct *res;
T
Tejun Heo 已提交
3377
	struct list_head *l = it->task_pos;
3378 3379

	/* If the iterator cg is NULL, we have no tasks */
T
Tejun Heo 已提交
3380
	if (!it->cset_pos)
3381 3382
		return NULL;
	res = list_entry(l, struct task_struct, cg_list);
T
Tejun Heo 已提交
3383 3384 3385 3386 3387 3388

	/*
	 * Advance iterator to find next entry.  cset->tasks is consumed
	 * first and then ->mg_tasks.  After ->mg_tasks, we move onto the
	 * next cset.
	 */
3389
	l = l->next;
T
Tejun Heo 已提交
3390

T
Tejun Heo 已提交
3391 3392
	if (l == it->tasks_head)
		l = it->mg_tasks_head->next;
T
Tejun Heo 已提交
3393

T
Tejun Heo 已提交
3394
	if (l == it->mg_tasks_head)
3395
		css_advance_task_iter(it);
T
Tejun Heo 已提交
3396
	else
T
Tejun Heo 已提交
3397
		it->task_pos = l;
T
Tejun Heo 已提交
3398

3399 3400 3401
	return res;
}

3402
/**
3403
 * css_task_iter_end - finish task iteration
3404 3405
 * @it: the task iterator to finish
 *
3406
 * Finish task iteration started by css_task_iter_start().
3407
 */
3408
void css_task_iter_end(struct css_task_iter *it)
3409
	__releases(css_set_rwsem)
3410
{
3411
	up_read(&css_set_rwsem);
3412 3413 3414
}

/**
3415 3416 3417
 * cgroup_trasnsfer_tasks - move tasks from one cgroup to another
 * @to: cgroup to which the tasks will be moved
 * @from: cgroup in which the tasks currently reside
3418
 *
3419 3420 3421 3422 3423
 * Locking rules between cgroup_post_fork() and the migration path
 * guarantee that, if a task is forking while being migrated, the new child
 * is guaranteed to be either visible in the source cgroup after the
 * parent's migration is complete or put into the target cgroup.  No task
 * can slip out of migration through forking.
3424
 */
3425
int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from)
3426
{
3427 3428
	LIST_HEAD(preloaded_csets);
	struct cgrp_cset_link *link;
3429
	struct css_task_iter it;
3430
	struct task_struct *task;
3431
	int ret;
3432

3433
	mutex_lock(&cgroup_mutex);
3434

3435 3436 3437 3438 3439
	/* all tasks in @from are being moved, all csets are source */
	down_read(&css_set_rwsem);
	list_for_each_entry(link, &from->cset_links, cset_link)
		cgroup_migrate_add_src(link->cset, to, &preloaded_csets);
	up_read(&css_set_rwsem);
3440

3441 3442 3443
	ret = cgroup_migrate_prepare_dst(to, &preloaded_csets);
	if (ret)
		goto out_err;
3444

3445 3446 3447 3448
	/*
	 * Migrate tasks one-by-one until @form is empty.  This fails iff
	 * ->can_attach() fails.
	 */
3449 3450 3451 3452 3453 3454 3455 3456
	do {
		css_task_iter_start(&from->dummy_css, &it);
		task = css_task_iter_next(&it);
		if (task)
			get_task_struct(task);
		css_task_iter_end(&it);

		if (task) {
3457
			ret = cgroup_migrate(to, task, false);
3458 3459 3460
			put_task_struct(task);
		}
	} while (task && !ret);
3461 3462
out_err:
	cgroup_migrate_finish(&preloaded_csets);
T
Tejun Heo 已提交
3463
	mutex_unlock(&cgroup_mutex);
3464
	return ret;
3465 3466
}

3467
/*
3468
 * Stuff for reading the 'tasks'/'procs' files.
3469 3470 3471 3472 3473 3474 3475 3476
 *
 * Reading this file can return large amounts of data if a cgroup has
 * *lots* of attached tasks. So it may need several calls to read(),
 * but we cannot guarantee that the information we produce is correct
 * unless we produce it entirely atomically.
 *
 */

3477 3478 3479 3480 3481 3482 3483 3484 3485 3486 3487 3488 3489 3490 3491 3492 3493 3494 3495 3496 3497 3498 3499 3500 3501 3502
/* which pidlist file are we talking about? */
enum cgroup_filetype {
	CGROUP_FILE_PROCS,
	CGROUP_FILE_TASKS,
};

/*
 * A pidlist is a list of pids that virtually represents the contents of one
 * of the cgroup files ("procs" or "tasks"). We keep a list of such pidlists,
 * a pair (one each for procs, tasks) for each pid namespace that's relevant
 * to the cgroup.
 */
struct cgroup_pidlist {
	/*
	 * used to find which pidlist is wanted. doesn't change as long as
	 * this particular list stays in the list.
	*/
	struct { enum cgroup_filetype type; struct pid_namespace *ns; } key;
	/* array of xids */
	pid_t *list;
	/* how many elements the above list has */
	int length;
	/* each of these stored in a list by its cgroup */
	struct list_head links;
	/* pointer to the cgroup we belong to, for list removal purposes */
	struct cgroup *owner;
3503 3504
	/* for delayed destruction */
	struct delayed_work destroy_dwork;
3505 3506
};

3507 3508 3509 3510 3511 3512 3513 3514 3515 3516 3517 3518 3519
/*
 * The following two functions "fix" the issue where there are more pids
 * than kmalloc will give memory for; in such cases, we use vmalloc/vfree.
 * TODO: replace with a kernel-wide solution to this problem
 */
#define PIDLIST_TOO_LARGE(c) ((c) * sizeof(pid_t) > (PAGE_SIZE * 2))
static void *pidlist_allocate(int count)
{
	if (PIDLIST_TOO_LARGE(count))
		return vmalloc(count * sizeof(pid_t));
	else
		return kmalloc(count * sizeof(pid_t), GFP_KERNEL);
}
3520

3521 3522 3523 3524 3525 3526 3527 3528
static void pidlist_free(void *p)
{
	if (is_vmalloc_addr(p))
		vfree(p);
	else
		kfree(p);
}

3529 3530 3531 3532 3533 3534 3535 3536 3537 3538 3539 3540 3541 3542 3543 3544 3545 3546 3547 3548 3549 3550 3551 3552 3553 3554 3555
/*
 * Used to destroy all pidlists lingering waiting for destroy timer.  None
 * should be left afterwards.
 */
static void cgroup_pidlist_destroy_all(struct cgroup *cgrp)
{
	struct cgroup_pidlist *l, *tmp_l;

	mutex_lock(&cgrp->pidlist_mutex);
	list_for_each_entry_safe(l, tmp_l, &cgrp->pidlists, links)
		mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork, 0);
	mutex_unlock(&cgrp->pidlist_mutex);

	flush_workqueue(cgroup_pidlist_destroy_wq);
	BUG_ON(!list_empty(&cgrp->pidlists));
}

static void cgroup_pidlist_destroy_work_fn(struct work_struct *work)
{
	struct delayed_work *dwork = to_delayed_work(work);
	struct cgroup_pidlist *l = container_of(dwork, struct cgroup_pidlist,
						destroy_dwork);
	struct cgroup_pidlist *tofree = NULL;

	mutex_lock(&l->owner->pidlist_mutex);

	/*
3556 3557
	 * Destroy iff we didn't get queued again.  The state won't change
	 * as destroy_dwork can only be queued while locked.
3558
	 */
3559
	if (!delayed_work_pending(dwork)) {
3560 3561 3562 3563 3564 3565 3566 3567 3568 3569
		list_del(&l->links);
		pidlist_free(l->list);
		put_pid_ns(l->key.ns);
		tofree = l;
	}

	mutex_unlock(&l->owner->pidlist_mutex);
	kfree(tofree);
}

3570
/*
3571
 * pidlist_uniq - given a kmalloc()ed list, strip out all duplicate entries
3572
 * Returns the number of unique elements.
3573
 */
3574
static int pidlist_uniq(pid_t *list, int length)
3575
{
3576 3577 3578 3579 3580 3581 3582 3583 3584 3585 3586 3587 3588 3589 3590 3591 3592 3593 3594 3595 3596 3597 3598 3599
	int src, dest = 1;

	/*
	 * we presume the 0th element is unique, so i starts at 1. trivial
	 * edge cases first; no work needs to be done for either
	 */
	if (length == 0 || length == 1)
		return length;
	/* src and dest walk down the list; dest counts unique elements */
	for (src = 1; src < length; src++) {
		/* find next unique element */
		while (list[src] == list[src-1]) {
			src++;
			if (src == length)
				goto after;
		}
		/* dest always points to where the next unique element goes */
		list[dest] = list[src];
		dest++;
	}
after:
	return dest;
}

3600 3601 3602 3603 3604 3605 3606 3607 3608 3609 3610 3611 3612 3613 3614 3615 3616 3617 3618 3619 3620 3621 3622 3623 3624 3625 3626 3627 3628 3629 3630 3631 3632
/*
 * The two pid files - task and cgroup.procs - guaranteed that the result
 * is sorted, which forced this whole pidlist fiasco.  As pid order is
 * different per namespace, each namespace needs differently sorted list,
 * making it impossible to use, for example, single rbtree of member tasks
 * sorted by task pointer.  As pidlists can be fairly large, allocating one
 * per open file is dangerous, so cgroup had to implement shared pool of
 * pidlists keyed by cgroup and namespace.
 *
 * All this extra complexity was caused by the original implementation
 * committing to an entirely unnecessary property.  In the long term, we
 * want to do away with it.  Explicitly scramble sort order if
 * sane_behavior so that no such expectation exists in the new interface.
 *
 * Scrambling is done by swapping every two consecutive bits, which is
 * non-identity one-to-one mapping which disturbs sort order sufficiently.
 */
static pid_t pid_fry(pid_t pid)
{
	unsigned a = pid & 0x55555555;
	unsigned b = pid & 0xAAAAAAAA;

	return (a << 1) | (b >> 1);
}

static pid_t cgroup_pid_fry(struct cgroup *cgrp, pid_t pid)
{
	if (cgroup_sane_behavior(cgrp))
		return pid_fry(pid);
	else
		return pid;
}

3633 3634 3635 3636 3637
static int cmppid(const void *a, const void *b)
{
	return *(pid_t *)a - *(pid_t *)b;
}

3638 3639 3640 3641 3642
static int fried_cmppid(const void *a, const void *b)
{
	return pid_fry(*(pid_t *)a) - pid_fry(*(pid_t *)b);
}

T
Tejun Heo 已提交
3643 3644 3645 3646 3647 3648 3649 3650 3651 3652 3653 3654 3655 3656 3657
static struct cgroup_pidlist *cgroup_pidlist_find(struct cgroup *cgrp,
						  enum cgroup_filetype type)
{
	struct cgroup_pidlist *l;
	/* don't need task_nsproxy() if we're looking at ourself */
	struct pid_namespace *ns = task_active_pid_ns(current);

	lockdep_assert_held(&cgrp->pidlist_mutex);

	list_for_each_entry(l, &cgrp->pidlists, links)
		if (l->key.type == type && l->key.ns == ns)
			return l;
	return NULL;
}

3658 3659 3660 3661 3662 3663
/*
 * find the appropriate pidlist for our purpose (given procs vs tasks)
 * returns with the lock on that pidlist already held, and takes care
 * of the use count, or returns NULL with no locks held if we're out of
 * memory.
 */
T
Tejun Heo 已提交
3664 3665
static struct cgroup_pidlist *cgroup_pidlist_find_create(struct cgroup *cgrp,
						enum cgroup_filetype type)
3666 3667
{
	struct cgroup_pidlist *l;
3668

T
Tejun Heo 已提交
3669 3670 3671 3672 3673 3674
	lockdep_assert_held(&cgrp->pidlist_mutex);

	l = cgroup_pidlist_find(cgrp, type);
	if (l)
		return l;

3675
	/* entry not found; create a new one */
3676
	l = kzalloc(sizeof(struct cgroup_pidlist), GFP_KERNEL);
T
Tejun Heo 已提交
3677
	if (!l)
3678
		return l;
T
Tejun Heo 已提交
3679

3680
	INIT_DELAYED_WORK(&l->destroy_dwork, cgroup_pidlist_destroy_work_fn);
3681
	l->key.type = type;
T
Tejun Heo 已提交
3682 3683
	/* don't need task_nsproxy() if we're looking at ourself */
	l->key.ns = get_pid_ns(task_active_pid_ns(current));
3684 3685 3686 3687 3688
	l->owner = cgrp;
	list_add(&l->links, &cgrp->pidlists);
	return l;
}

3689 3690 3691
/*
 * Load a cgroup's pidarray with either procs' tgids or tasks' pids
 */
3692 3693
static int pidlist_array_load(struct cgroup *cgrp, enum cgroup_filetype type,
			      struct cgroup_pidlist **lp)
3694 3695 3696 3697
{
	pid_t *array;
	int length;
	int pid, n = 0; /* used for populating the array */
3698
	struct css_task_iter it;
3699
	struct task_struct *tsk;
3700 3701
	struct cgroup_pidlist *l;

3702 3703
	lockdep_assert_held(&cgrp->pidlist_mutex);

3704 3705 3706 3707 3708 3709 3710
	/*
	 * If cgroup gets more users after we read count, we won't have
	 * enough space - tough.  This race is indistinguishable to the
	 * caller from the case that the additional cgroup users didn't
	 * show up until sometime later on.
	 */
	length = cgroup_task_count(cgrp);
3711
	array = pidlist_allocate(length);
3712 3713 3714
	if (!array)
		return -ENOMEM;
	/* now, populate the array */
3715 3716
	css_task_iter_start(&cgrp->dummy_css, &it);
	while ((tsk = css_task_iter_next(&it))) {
3717
		if (unlikely(n == length))
3718
			break;
3719
		/* get tgid or pid for procs or tasks file respectively */
3720 3721 3722 3723
		if (type == CGROUP_FILE_PROCS)
			pid = task_tgid_vnr(tsk);
		else
			pid = task_pid_vnr(tsk);
3724 3725
		if (pid > 0) /* make sure to only use valid results */
			array[n++] = pid;
3726
	}
3727
	css_task_iter_end(&it);
3728 3729
	length = n;
	/* now sort & (if procs) strip out duplicates */
3730 3731 3732 3733
	if (cgroup_sane_behavior(cgrp))
		sort(array, length, sizeof(pid_t), fried_cmppid, NULL);
	else
		sort(array, length, sizeof(pid_t), cmppid, NULL);
3734
	if (type == CGROUP_FILE_PROCS)
3735
		length = pidlist_uniq(array, length);
T
Tejun Heo 已提交
3736 3737

	l = cgroup_pidlist_find_create(cgrp, type);
3738
	if (!l) {
T
Tejun Heo 已提交
3739
		mutex_unlock(&cgrp->pidlist_mutex);
3740
		pidlist_free(array);
3741
		return -ENOMEM;
3742
	}
T
Tejun Heo 已提交
3743 3744

	/* store array, freeing old if necessary */
3745
	pidlist_free(l->list);
3746 3747
	l->list = array;
	l->length = length;
3748
	*lp = l;
3749
	return 0;
3750 3751
}

B
Balbir Singh 已提交
3752
/**
L
Li Zefan 已提交
3753
 * cgroupstats_build - build and fill cgroupstats
B
Balbir Singh 已提交
3754 3755 3756
 * @stats: cgroupstats to fill information into
 * @dentry: A dentry entry belonging to the cgroup for which stats have
 * been requested.
L
Li Zefan 已提交
3757 3758 3759
 *
 * Build and fill cgroupstats so that taskstats can export it to user
 * space.
B
Balbir Singh 已提交
3760 3761 3762
 */
int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
{
T
Tejun Heo 已提交
3763
	struct kernfs_node *kn = kernfs_node_from_dentry(dentry);
3764
	struct cgroup *cgrp;
3765
	struct css_task_iter it;
B
Balbir Singh 已提交
3766
	struct task_struct *tsk;
3767

T
Tejun Heo 已提交
3768 3769 3770 3771 3772
	/* it should be kernfs_node belonging to cgroupfs and is a directory */
	if (dentry->d_sb->s_type != &cgroup_fs_type || !kn ||
	    kernfs_type(kn) != KERNFS_DIR)
		return -EINVAL;

3773 3774
	mutex_lock(&cgroup_mutex);

B
Balbir Singh 已提交
3775
	/*
T
Tejun Heo 已提交
3776 3777 3778
	 * We aren't being called from kernfs and there's no guarantee on
	 * @kn->priv's validity.  For this and css_tryget_from_dir(),
	 * @kn->priv is RCU safe.  Let's do the RCU dancing.
B
Balbir Singh 已提交
3779
	 */
T
Tejun Heo 已提交
3780 3781
	rcu_read_lock();
	cgrp = rcu_dereference(kn->priv);
3782
	if (!cgrp || cgroup_is_dead(cgrp)) {
T
Tejun Heo 已提交
3783
		rcu_read_unlock();
3784
		mutex_unlock(&cgroup_mutex);
T
Tejun Heo 已提交
3785 3786
		return -ENOENT;
	}
3787
	rcu_read_unlock();
B
Balbir Singh 已提交
3788

3789 3790
	css_task_iter_start(&cgrp->dummy_css, &it);
	while ((tsk = css_task_iter_next(&it))) {
B
Balbir Singh 已提交
3791 3792 3793 3794 3795 3796 3797 3798 3799 3800 3801 3802 3803 3804 3805 3806 3807 3808 3809
		switch (tsk->state) {
		case TASK_RUNNING:
			stats->nr_running++;
			break;
		case TASK_INTERRUPTIBLE:
			stats->nr_sleeping++;
			break;
		case TASK_UNINTERRUPTIBLE:
			stats->nr_uninterruptible++;
			break;
		case TASK_STOPPED:
			stats->nr_stopped++;
			break;
		default:
			if (delayacct_is_task_waiting_on_io(tsk))
				stats->nr_io_wait++;
			break;
		}
	}
3810
	css_task_iter_end(&it);
B
Balbir Singh 已提交
3811

3812
	mutex_unlock(&cgroup_mutex);
T
Tejun Heo 已提交
3813
	return 0;
B
Balbir Singh 已提交
3814 3815
}

3816

3817
/*
3818
 * seq_file methods for the tasks/procs files. The seq_file position is the
3819
 * next pid to display; the seq_file iterator is a pointer to the pid
3820
 * in the cgroup->l->list array.
3821
 */
3822

3823
static void *cgroup_pidlist_start(struct seq_file *s, loff_t *pos)
3824
{
3825 3826 3827 3828 3829 3830
	/*
	 * Initially we receive a position value that corresponds to
	 * one more than the last pid shown (or 0 on the first call or
	 * after a seek to the start). Use a binary-search to find the
	 * next pid to display, if any
	 */
T
Tejun Heo 已提交
3831
	struct kernfs_open_file *of = s->private;
3832
	struct cgroup *cgrp = seq_css(s)->cgroup;
3833
	struct cgroup_pidlist *l;
3834
	enum cgroup_filetype type = seq_cft(s)->private;
3835
	int index = 0, pid = *pos;
3836 3837 3838 3839 3840
	int *iter, ret;

	mutex_lock(&cgrp->pidlist_mutex);

	/*
3841
	 * !NULL @of->priv indicates that this isn't the first start()
3842
	 * after open.  If the matching pidlist is around, we can use that.
3843
	 * Look for it.  Note that @of->priv can't be used directly.  It
3844 3845
	 * could already have been destroyed.
	 */
3846 3847
	if (of->priv)
		of->priv = cgroup_pidlist_find(cgrp, type);
3848 3849 3850 3851 3852

	/*
	 * Either this is the first start() after open or the matching
	 * pidlist has been destroyed inbetween.  Create a new one.
	 */
3853 3854 3855
	if (!of->priv) {
		ret = pidlist_array_load(cgrp, type,
					 (struct cgroup_pidlist **)&of->priv);
3856 3857 3858
		if (ret)
			return ERR_PTR(ret);
	}
3859
	l = of->priv;
3860 3861

	if (pid) {
3862
		int end = l->length;
S
Stephen Rothwell 已提交
3863

3864 3865
		while (index < end) {
			int mid = (index + end) / 2;
3866
			if (cgroup_pid_fry(cgrp, l->list[mid]) == pid) {
3867 3868
				index = mid;
				break;
3869
			} else if (cgroup_pid_fry(cgrp, l->list[mid]) <= pid)
3870 3871 3872 3873 3874 3875
				index = mid + 1;
			else
				end = mid;
		}
	}
	/* If we're off the end of the array, we're done */
3876
	if (index >= l->length)
3877 3878
		return NULL;
	/* Update the abstract position to be the actual pid that we found */
3879
	iter = l->list + index;
3880
	*pos = cgroup_pid_fry(cgrp, *iter);
3881 3882 3883
	return iter;
}

3884
static void cgroup_pidlist_stop(struct seq_file *s, void *v)
3885
{
T
Tejun Heo 已提交
3886
	struct kernfs_open_file *of = s->private;
3887
	struct cgroup_pidlist *l = of->priv;
3888

3889 3890
	if (l)
		mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork,
3891
				 CGROUP_PIDLIST_DESTROY_DELAY);
3892
	mutex_unlock(&seq_css(s)->cgroup->pidlist_mutex);
3893 3894
}

3895
static void *cgroup_pidlist_next(struct seq_file *s, void *v, loff_t *pos)
3896
{
T
Tejun Heo 已提交
3897
	struct kernfs_open_file *of = s->private;
3898
	struct cgroup_pidlist *l = of->priv;
3899 3900
	pid_t *p = v;
	pid_t *end = l->list + l->length;
3901 3902 3903 3904 3905 3906 3907 3908
	/*
	 * Advance to the next pid in the array. If this goes off the
	 * end, we're done
	 */
	p++;
	if (p >= end) {
		return NULL;
	} else {
3909
		*pos = cgroup_pid_fry(seq_css(s)->cgroup, *p);
3910 3911 3912 3913
		return p;
	}
}

3914
static int cgroup_pidlist_show(struct seq_file *s, void *v)
3915 3916 3917
{
	return seq_printf(s, "%d\n", *(int *)v);
}
3918

3919 3920
static u64 cgroup_read_notify_on_release(struct cgroup_subsys_state *css,
					 struct cftype *cft)
3921
{
3922
	return notify_on_release(css->cgroup);
3923 3924
}

3925 3926
static int cgroup_write_notify_on_release(struct cgroup_subsys_state *css,
					  struct cftype *cft, u64 val)
3927
{
3928
	clear_bit(CGRP_RELEASABLE, &css->cgroup->flags);
3929
	if (val)
3930
		set_bit(CGRP_NOTIFY_ON_RELEASE, &css->cgroup->flags);
3931
	else
3932
		clear_bit(CGRP_NOTIFY_ON_RELEASE, &css->cgroup->flags);
3933 3934 3935
	return 0;
}

3936 3937
static u64 cgroup_clone_children_read(struct cgroup_subsys_state *css,
				      struct cftype *cft)
3938
{
3939
	return test_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
3940 3941
}

3942 3943
static int cgroup_clone_children_write(struct cgroup_subsys_state *css,
				       struct cftype *cft, u64 val)
3944 3945
{
	if (val)
3946
		set_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
3947
	else
3948
		clear_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
3949 3950 3951
	return 0;
}

3952
static struct cftype cgroup_base_files[] = {
3953
	{
3954
		.name = "cgroup.procs",
3955 3956 3957 3958
		.seq_start = cgroup_pidlist_start,
		.seq_next = cgroup_pidlist_next,
		.seq_stop = cgroup_pidlist_stop,
		.seq_show = cgroup_pidlist_show,
3959
		.private = CGROUP_FILE_PROCS,
B
Ben Blum 已提交
3960 3961
		.write_u64 = cgroup_procs_write,
		.mode = S_IRUGO | S_IWUSR,
3962
	},
3963 3964
	{
		.name = "cgroup.clone_children",
3965
		.flags = CFTYPE_INSANE,
3966 3967 3968
		.read_u64 = cgroup_clone_children_read,
		.write_u64 = cgroup_clone_children_write,
	},
3969 3970 3971
	{
		.name = "cgroup.sane_behavior",
		.flags = CFTYPE_ONLY_ON_ROOT,
3972
		.seq_show = cgroup_sane_behavior_show,
3973
	},
3974 3975 3976 3977 3978 3979 3980 3981 3982 3983 3984 3985 3986 3987 3988 3989
	{
		.name = "cgroup.controllers",
		.flags = CFTYPE_ONLY_ON_DFL | CFTYPE_ONLY_ON_ROOT,
		.seq_show = cgroup_root_controllers_show,
	},
	{
		.name = "cgroup.controllers",
		.flags = CFTYPE_ONLY_ON_DFL | CFTYPE_NOT_ON_ROOT,
		.seq_show = cgroup_controllers_show,
	},
	{
		.name = "cgroup.subtree_control",
		.flags = CFTYPE_ONLY_ON_DFL,
		.seq_show = cgroup_subtree_control_show,
		.write_string = cgroup_subtree_control_write,
	},
3990 3991 3992 3993 3994
	{
		.name = "cgroup.populated",
		.flags = CFTYPE_ONLY_ON_DFL | CFTYPE_NOT_ON_ROOT,
		.seq_show = cgroup_populated_show,
	},
3995 3996 3997 3998 3999 4000 4001 4002 4003

	/*
	 * Historical crazy stuff.  These don't have "cgroup."  prefix and
	 * don't exist if sane_behavior.  If you're depending on these, be
	 * prepared to be burned.
	 */
	{
		.name = "tasks",
		.flags = CFTYPE_INSANE,		/* use "procs" instead */
4004 4005 4006 4007
		.seq_start = cgroup_pidlist_start,
		.seq_next = cgroup_pidlist_next,
		.seq_stop = cgroup_pidlist_stop,
		.seq_show = cgroup_pidlist_show,
4008
		.private = CGROUP_FILE_TASKS,
4009 4010 4011 4012 4013 4014 4015 4016 4017
		.write_u64 = cgroup_tasks_write,
		.mode = S_IRUGO | S_IWUSR,
	},
	{
		.name = "notify_on_release",
		.flags = CFTYPE_INSANE,
		.read_u64 = cgroup_read_notify_on_release,
		.write_u64 = cgroup_write_notify_on_release,
	},
4018 4019
	{
		.name = "release_agent",
4020
		.flags = CFTYPE_INSANE | CFTYPE_ONLY_ON_ROOT,
4021
		.seq_show = cgroup_release_agent_show,
4022
		.write_string = cgroup_release_agent_write,
4023
		.max_write_len = PATH_MAX - 1,
4024
	},
T
Tejun Heo 已提交
4025
	{ }	/* terminate */
4026 4027
};

4028
/**
4029
 * cgroup_populate_dir - create subsys files in a cgroup directory
4030 4031
 * @cgrp: target cgroup
 * @subsys_mask: mask of the subsystem ids whose files should be added
4032 4033
 *
 * On failure, no file is added.
4034
 */
4035
static int cgroup_populate_dir(struct cgroup *cgrp, unsigned int subsys_mask)
4036 4037
{
	struct cgroup_subsys *ss;
4038
	int i, ret = 0;
4039

4040
	/* process cftsets of each subsystem */
4041
	for_each_subsys(ss, i) {
T
Tejun Heo 已提交
4042
		struct cftype *cfts;
4043

4044
		if (!(subsys_mask & (1 << i)))
4045
			continue;
4046

T
Tejun Heo 已提交
4047 4048
		list_for_each_entry(cfts, &ss->cfts, node) {
			ret = cgroup_addrm_files(cgrp, cfts, true);
4049 4050 4051
			if (ret < 0)
				goto err;
		}
4052 4053
	}
	return 0;
4054 4055 4056
err:
	cgroup_clear_dir(cgrp, subsys_mask);
	return ret;
4057 4058
}

4059 4060 4061 4062 4063 4064 4065 4066 4067 4068 4069 4070 4071 4072 4073 4074 4075 4076 4077 4078 4079 4080
/*
 * css destruction is four-stage process.
 *
 * 1. Destruction starts.  Killing of the percpu_ref is initiated.
 *    Implemented in kill_css().
 *
 * 2. When the percpu_ref is confirmed to be visible as killed on all CPUs
 *    and thus css_tryget() is guaranteed to fail, the css can be offlined
 *    by invoking offline_css().  After offlining, the base ref is put.
 *    Implemented in css_killed_work_fn().
 *
 * 3. When the percpu_ref reaches zero, the only possible remaining
 *    accessors are inside RCU read sections.  css_release() schedules the
 *    RCU callback.
 *
 * 4. After the grace period, the css can be freed.  Implemented in
 *    css_free_work_fn().
 *
 * It is actually hairier because both step 2 and 4 require process context
 * and thus involve punting to css->destroy_work adding two additional
 * steps to the already complex sequence.
 */
4081
static void css_free_work_fn(struct work_struct *work)
4082 4083
{
	struct cgroup_subsys_state *css =
4084
		container_of(work, struct cgroup_subsys_state, destroy_work);
4085
	struct cgroup *cgrp = css->cgroup;
4086

4087 4088 4089
	if (css->parent)
		css_put(css->parent);

4090
	css->ss->css_free(css);
T
Tejun Heo 已提交
4091
	cgroup_put(cgrp);
4092 4093
}

4094
static void css_free_rcu_fn(struct rcu_head *rcu_head)
4095 4096
{
	struct cgroup_subsys_state *css =
4097
		container_of(rcu_head, struct cgroup_subsys_state, rcu_head);
4098

4099
	INIT_WORK(&css->destroy_work, css_free_work_fn);
4100
	queue_work(cgroup_destroy_wq, &css->destroy_work);
4101 4102
}

4103 4104 4105 4106 4107
static void css_release(struct percpu_ref *ref)
{
	struct cgroup_subsys_state *css =
		container_of(ref, struct cgroup_subsys_state, refcnt);

4108
	RCU_INIT_POINTER(css->cgroup->subsys[css->ss->id], NULL);
4109
	call_rcu(&css->rcu_head, css_free_rcu_fn);
4110 4111
}

4112 4113
static void init_css(struct cgroup_subsys_state *css, struct cgroup_subsys *ss,
		     struct cgroup *cgrp)
4114
{
4115
	css->cgroup = cgrp;
4116
	css->ss = ss;
4117
	css->flags = 0;
4118 4119

	if (cgrp->parent)
4120
		css->parent = cgroup_css(cgrp->parent, ss);
4121
	else
4122
		css->flags |= CSS_ROOT;
4123

4124
	BUG_ON(cgroup_css(cgrp, ss));
4125 4126
}

4127
/* invoke ->css_online() on a new CSS and mark it online if successful */
4128
static int online_css(struct cgroup_subsys_state *css)
4129
{
4130
	struct cgroup_subsys *ss = css->ss;
T
Tejun Heo 已提交
4131 4132
	int ret = 0;

T
Tejun Heo 已提交
4133
	lockdep_assert_held(&cgroup_tree_mutex);
4134 4135
	lockdep_assert_held(&cgroup_mutex);

4136
	if (ss->css_online)
4137
		ret = ss->css_online(css);
4138
	if (!ret) {
4139
		css->flags |= CSS_ONLINE;
4140
		css->cgroup->nr_css++;
4141
		rcu_assign_pointer(css->cgroup->subsys[ss->id], css);
4142
	}
T
Tejun Heo 已提交
4143
	return ret;
4144 4145
}

4146
/* if the CSS is online, invoke ->css_offline() on it and mark it offline */
4147
static void offline_css(struct cgroup_subsys_state *css)
4148
{
4149
	struct cgroup_subsys *ss = css->ss;
4150

T
Tejun Heo 已提交
4151
	lockdep_assert_held(&cgroup_tree_mutex);
4152 4153 4154 4155 4156
	lockdep_assert_held(&cgroup_mutex);

	if (!(css->flags & CSS_ONLINE))
		return;

4157
	if (ss->css_offline)
4158
		ss->css_offline(css);
4159

4160
	css->flags &= ~CSS_ONLINE;
4161
	css->cgroup->nr_css--;
4162
	RCU_INIT_POINTER(css->cgroup->subsys[ss->id], NULL);
4163 4164

	wake_up_all(&css->cgroup->offline_waitq);
4165 4166
}

4167 4168 4169 4170 4171 4172 4173 4174 4175 4176 4177 4178 4179 4180 4181 4182 4183 4184 4185 4186 4187
/**
 * create_css - create a cgroup_subsys_state
 * @cgrp: the cgroup new css will be associated with
 * @ss: the subsys of new css
 *
 * Create a new css associated with @cgrp - @ss pair.  On success, the new
 * css is online and installed in @cgrp with all interface files created.
 * Returns 0 on success, -errno on failure.
 */
static int create_css(struct cgroup *cgrp, struct cgroup_subsys *ss)
{
	struct cgroup *parent = cgrp->parent;
	struct cgroup_subsys_state *css;
	int err;

	lockdep_assert_held(&cgroup_mutex);

	css = ss->css_alloc(cgroup_css(parent, ss));
	if (IS_ERR(css))
		return PTR_ERR(css);

4188 4189 4190 4191
	init_css(css, ss, cgrp);
	cgroup_get(cgrp);
	css_get(css->parent);

4192 4193
	err = percpu_ref_init(&css->refcnt, css_release);
	if (err)
4194
		goto err_free_css;
4195

4196
	err = cgroup_populate_dir(cgrp, 1 << ss->id);
4197
	if (err)
4198
		goto err_free_percpu_ref;
4199 4200 4201

	err = online_css(css);
	if (err)
4202
		goto err_clear_dir;
4203 4204 4205

	if (ss->broken_hierarchy && !ss->warned_broken_hierarchy &&
	    parent->parent) {
4206
		pr_warn("%s (%d) created nested cgroup for controller \"%s\" which has incomplete hierarchy support. Nested cgroups may change behavior in the future.\n",
4207
			current->comm, current->pid, ss->name);
4208
		if (!strcmp(ss->name, "memory"))
4209
			pr_warn("\"memory\" requires setting use_hierarchy to 1 on the root\n");
4210 4211 4212 4213 4214
		ss->warned_broken_hierarchy = true;
	}

	return 0;

4215
err_clear_dir:
4216
	cgroup_clear_dir(css->cgroup, 1 << css->ss->id);
4217
err_free_percpu_ref:
4218
	percpu_ref_cancel_init(&css->refcnt);
4219
err_free_css:
4220
	call_rcu(&css->rcu_head, css_free_rcu_fn);
4221 4222 4223
	return err;
}

T
Tejun Heo 已提交
4224
/**
L
Li Zefan 已提交
4225 4226
 * cgroup_create - create a cgroup
 * @parent: cgroup that will be parent of the new cgroup
T
Tejun Heo 已提交
4227
 * @name: name of the new cgroup
T
Tejun Heo 已提交
4228
 * @mode: mode to set on new cgroup
4229
 */
T
Tejun Heo 已提交
4230
static long cgroup_create(struct cgroup *parent, const char *name,
T
Tejun Heo 已提交
4231
			  umode_t mode)
4232
{
4233
	struct cgroup *cgrp;
4234
	struct cgroup_root *root = parent->root;
4235
	int ssid, err;
4236
	struct cgroup_subsys *ss;
T
Tejun Heo 已提交
4237
	struct kernfs_node *kn;
4238

T
Tejun Heo 已提交
4239
	/* allocate the cgroup and its ID, 0 is reserved for the root */
4240 4241
	cgrp = kzalloc(sizeof(*cgrp), GFP_KERNEL);
	if (!cgrp)
4242 4243
		return -ENOMEM;

T
Tejun Heo 已提交
4244
	mutex_lock(&cgroup_tree_mutex);
4245

4246 4247 4248 4249 4250 4251 4252 4253 4254
	/*
	 * Only live parents can have children.  Note that the liveliness
	 * check isn't strictly necessary because cgroup_mkdir() and
	 * cgroup_rmdir() are fully synchronized by i_mutex; however, do it
	 * anyway so that locking is contained inside cgroup proper and we
	 * don't get nasty surprises if we ever grow another caller.
	 */
	if (!cgroup_lock_live_group(parent)) {
		err = -ENODEV;
T
Tejun Heo 已提交
4255
		goto err_unlock_tree;
4256 4257 4258 4259 4260 4261
	}

	/*
	 * Temporarily set the pointer to NULL, so idr_find() won't return
	 * a half-baked cgroup.
	 */
4262
	cgrp->id = cgroup_idr_alloc(&root->cgroup_idr, NULL, 2, 0, GFP_NOWAIT);
4263 4264 4265
	if (cgrp->id < 0) {
		err = -ENOMEM;
		goto err_unlock;
4266 4267
	}

4268
	init_cgroup_housekeeping(cgrp);
4269

4270
	cgrp->parent = parent;
4271
	cgrp->dummy_css.parent = &parent->dummy_css;
4272
	cgrp->root = parent->root;
4273

4274 4275 4276
	if (notify_on_release(parent))
		set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);

4277 4278
	if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &parent->flags))
		set_bit(CGRP_CPUSET_CLONE_CHILDREN, &cgrp->flags);
4279

T
Tejun Heo 已提交
4280
	/* create the directory */
T
Tejun Heo 已提交
4281
	kn = kernfs_create_dir(parent->kn, name, mode, cgrp);
T
Tejun Heo 已提交
4282 4283
	if (IS_ERR(kn)) {
		err = PTR_ERR(kn);
4284
		goto err_free_id;
T
Tejun Heo 已提交
4285 4286
	}
	cgrp->kn = kn;
4287

4288
	/*
4289 4290
	 * This extra ref will be put in cgroup_free_fn() and guarantees
	 * that @cgrp->kn is always accessible.
4291
	 */
4292
	kernfs_get(kn);
4293

4294
	cgrp->serial_nr = cgroup_serial_nr_next++;
4295

4296 4297
	/* allocation complete, commit to creation */
	list_add_tail_rcu(&cgrp->sibling, &cgrp->parent->children);
4298
	atomic_inc(&root->nr_cgrps);
4299
	cgroup_get(parent);
4300

4301 4302 4303 4304
	/*
	 * @cgrp is now fully operational.  If something fails after this
	 * point, it'll be released via the normal destruction path.
	 */
4305
	cgroup_idr_replace(&root->cgroup_idr, cgrp, cgrp->id);
4306

4307 4308 4309 4310
	err = cgroup_kn_set_ugid(kn);
	if (err)
		goto err_destroy;

4311
	err = cgroup_addrm_files(cgrp, cgroup_base_files, true);
4312 4313 4314
	if (err)
		goto err_destroy;

4315
	/* let's create and online css's */
T
Tejun Heo 已提交
4316
	for_each_subsys(ss, ssid) {
4317
		if (parent->child_subsys_mask & (1 << ssid)) {
T
Tejun Heo 已提交
4318 4319 4320 4321
			err = create_css(cgrp, ss);
			if (err)
				goto err_destroy;
		}
4322
	}
4323

4324 4325 4326 4327 4328 4329
	/*
	 * On the default hierarchy, a child doesn't automatically inherit
	 * child_subsys_mask from the parent.  Each is configured manually.
	 */
	if (!cgroup_on_dfl(cgrp))
		cgrp->child_subsys_mask = parent->child_subsys_mask;
4330

T
Tejun Heo 已提交
4331 4332
	kernfs_activate(kn);

4333
	mutex_unlock(&cgroup_mutex);
T
Tejun Heo 已提交
4334
	mutex_unlock(&cgroup_tree_mutex);
4335 4336 4337

	return 0;

T
Tejun Heo 已提交
4338
err_free_id:
4339
	cgroup_idr_remove(&root->cgroup_idr, cgrp->id);
4340 4341
err_unlock:
	mutex_unlock(&cgroup_mutex);
T
Tejun Heo 已提交
4342 4343
err_unlock_tree:
	mutex_unlock(&cgroup_tree_mutex);
4344
	kfree(cgrp);
4345
	return err;
4346 4347 4348 4349

err_destroy:
	cgroup_destroy_locked(cgrp);
	mutex_unlock(&cgroup_mutex);
T
Tejun Heo 已提交
4350
	mutex_unlock(&cgroup_tree_mutex);
4351
	return err;
4352 4353
}

T
Tejun Heo 已提交
4354 4355
static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name,
			umode_t mode)
4356
{
T
Tejun Heo 已提交
4357
	struct cgroup *parent = parent_kn->priv;
4358
	int ret;
4359

4360 4361 4362 4363 4364 4365 4366 4367
	/*
	 * cgroup_create() grabs cgroup_tree_mutex which nests outside
	 * kernfs active_ref and cgroup_create() already synchronizes
	 * properly against removal through cgroup_lock_live_group().
	 * Break it before calling cgroup_create().
	 */
	cgroup_get(parent);
	kernfs_break_active_protection(parent_kn);
4368

4369 4370 4371 4372 4373
	ret = cgroup_create(parent, name, mode);

	kernfs_unbreak_active_protection(parent_kn);
	cgroup_put(parent);
	return ret;
4374 4375
}

4376 4377 4378 4379 4380
/*
 * This is called when the refcnt of a css is confirmed to be killed.
 * css_tryget() is now guaranteed to fail.
 */
static void css_killed_work_fn(struct work_struct *work)
4381
{
4382 4383 4384
	struct cgroup_subsys_state *css =
		container_of(work, struct cgroup_subsys_state, destroy_work);
	struct cgroup *cgrp = css->cgroup;
4385

T
Tejun Heo 已提交
4386
	mutex_lock(&cgroup_tree_mutex);
4387 4388
	mutex_lock(&cgroup_mutex);

4389 4390 4391 4392 4393 4394
	/*
	 * css_tryget() is guaranteed to fail now.  Tell subsystems to
	 * initate destruction.
	 */
	offline_css(css);

4395 4396 4397 4398 4399
	/*
	 * If @cgrp is marked dead, it's waiting for refs of all css's to
	 * be disabled before proceeding to the second phase of cgroup
	 * destruction.  If we are the last one, kick it off.
	 */
4400
	if (!cgrp->nr_css && cgroup_is_dead(cgrp))
4401 4402 4403
		cgroup_destroy_css_killed(cgrp);

	mutex_unlock(&cgroup_mutex);
T
Tejun Heo 已提交
4404
	mutex_unlock(&cgroup_tree_mutex);
4405 4406 4407 4408 4409 4410 4411 4412 4413

	/*
	 * Put the css refs from kill_css().  Each css holds an extra
	 * reference to the cgroup's dentry and cgroup removal proceeds
	 * regardless of css refs.  On the last put of each css, whenever
	 * that may be, the extra dentry ref is put so that dentry
	 * destruction happens only after all css's are released.
	 */
	css_put(css);
4414 4415
}

4416 4417
/* css kill confirmation processing requires process context, bounce */
static void css_killed_ref_fn(struct percpu_ref *ref)
4418 4419 4420 4421
{
	struct cgroup_subsys_state *css =
		container_of(ref, struct cgroup_subsys_state, refcnt);

4422
	INIT_WORK(&css->destroy_work, css_killed_work_fn);
4423
	queue_work(cgroup_destroy_wq, &css->destroy_work);
4424 4425
}

4426 4427 4428 4429 4430 4431 4432 4433 4434 4435
/**
 * kill_css - destroy a css
 * @css: css to destroy
 *
 * This function initiates destruction of @css by removing cgroup interface
 * files and putting its base reference.  ->css_offline() will be invoked
 * asynchronously once css_tryget() is guaranteed to fail and when the
 * reference count reaches zero, @css will be released.
 */
static void kill_css(struct cgroup_subsys_state *css)
T
Tejun Heo 已提交
4436
{
4437 4438
	lockdep_assert_held(&cgroup_tree_mutex);

T
Tejun Heo 已提交
4439 4440 4441 4442
	/*
	 * This must happen before css is disassociated with its cgroup.
	 * See seq_css() for details.
	 */
4443
	cgroup_clear_dir(css->cgroup, 1 << css->ss->id);
4444

T
Tejun Heo 已提交
4445 4446 4447 4448 4449 4450 4451 4452 4453 4454 4455 4456 4457 4458 4459 4460 4461
	/*
	 * Killing would put the base ref, but we need to keep it alive
	 * until after ->css_offline().
	 */
	css_get(css);

	/*
	 * cgroup core guarantees that, by the time ->css_offline() is
	 * invoked, no new css reference will be given out via
	 * css_tryget().  We can't simply call percpu_ref_kill() and
	 * proceed to offlining css's because percpu_ref_kill() doesn't
	 * guarantee that the ref is seen as killed on all CPUs on return.
	 *
	 * Use percpu_ref_kill_and_confirm() to get notifications as each
	 * css is confirmed to be seen as killed on all CPUs.
	 */
	percpu_ref_kill_and_confirm(&css->refcnt, css_killed_ref_fn);
4462 4463 4464 4465 4466 4467 4468 4469 4470 4471 4472 4473 4474 4475 4476 4477 4478 4479 4480 4481 4482 4483 4484 4485 4486 4487
}

/**
 * cgroup_destroy_locked - the first stage of cgroup destruction
 * @cgrp: cgroup to be destroyed
 *
 * css's make use of percpu refcnts whose killing latency shouldn't be
 * exposed to userland and are RCU protected.  Also, cgroup core needs to
 * guarantee that css_tryget() won't succeed by the time ->css_offline() is
 * invoked.  To satisfy all the requirements, destruction is implemented in
 * the following two steps.
 *
 * s1. Verify @cgrp can be destroyed and mark it dying.  Remove all
 *     userland visible parts and start killing the percpu refcnts of
 *     css's.  Set up so that the next stage will be kicked off once all
 *     the percpu refcnts are confirmed to be killed.
 *
 * s2. Invoke ->css_offline(), mark the cgroup dead and proceed with the
 *     rest of destruction.  Once all cgroup references are gone, the
 *     cgroup is RCU-freed.
 *
 * This function implements s1.  After this step, @cgrp is gone as far as
 * the userland is concerned and a new cgroup with the same name may be
 * created.  As cgroup doesn't care about the names internally, this
 * doesn't cause any problem.
 */
4488 4489
static int cgroup_destroy_locked(struct cgroup *cgrp)
	__releases(&cgroup_mutex) __acquires(&cgroup_mutex)
4490
{
4491
	struct cgroup *child;
T
Tejun Heo 已提交
4492
	struct cgroup_subsys_state *css;
4493
	bool empty;
T
Tejun Heo 已提交
4494
	int ssid;
4495

T
Tejun Heo 已提交
4496
	lockdep_assert_held(&cgroup_tree_mutex);
4497 4498
	lockdep_assert_held(&cgroup_mutex);

4499
	/*
4500
	 * css_set_rwsem synchronizes access to ->cset_links and prevents
4501
	 * @cgrp from being removed while put_css_set() is in progress.
4502
	 */
4503
	down_read(&css_set_rwsem);
4504
	empty = list_empty(&cgrp->cset_links);
4505
	up_read(&css_set_rwsem);
4506
	if (!empty)
4507
		return -EBUSY;
L
Li Zefan 已提交
4508

4509 4510 4511 4512 4513 4514 4515 4516 4517 4518 4519 4520 4521 4522 4523 4524
	/*
	 * Make sure there's no live children.  We can't test ->children
	 * emptiness as dead children linger on it while being destroyed;
	 * otherwise, "rmdir parent/child parent" may fail with -EBUSY.
	 */
	empty = true;
	rcu_read_lock();
	list_for_each_entry_rcu(child, &cgrp->children, sibling) {
		empty = cgroup_is_dead(child);
		if (!empty)
			break;
	}
	rcu_read_unlock();
	if (!empty)
		return -EBUSY;

4525 4526 4527
	/*
	 * Mark @cgrp dead.  This prevents further task migration and child
	 * creation by disabling cgroup_lock_live_group().  Note that
4528
	 * CGRP_DEAD assertion is depended upon by css_next_child() to
4529
	 * resume iteration after dropping RCU read lock.  See
4530
	 * css_next_child() for details.
4531
	 */
4532
	set_bit(CGRP_DEAD, &cgrp->flags);
4533

4534
	/*
T
Tejun Heo 已提交
4535 4536
	 * Initiate massacre of all css's.  cgroup_destroy_css_killed()
	 * will be invoked to perform the rest of destruction once the
4537 4538
	 * percpu refs of all css's are confirmed to be killed.  This
	 * involves removing the subsystem's files, drop cgroup_mutex.
4539
	 */
4540
	mutex_unlock(&cgroup_mutex);
T
Tejun Heo 已提交
4541 4542
	for_each_css(css, ssid, cgrp)
		kill_css(css);
4543
	mutex_lock(&cgroup_mutex);
4544 4545 4546 4547 4548 4549 4550 4551

	/* CGRP_DEAD is set, remove from ->release_list for the last time */
	raw_spin_lock(&release_list_lock);
	if (!list_empty(&cgrp->release_list))
		list_del_init(&cgrp->release_list);
	raw_spin_unlock(&release_list_lock);

	/*
4552 4553 4554 4555 4556 4557 4558 4559
	 * If @cgrp has css's attached, the second stage of cgroup
	 * destruction is kicked off from css_killed_work_fn() after the
	 * refs of all attached css's are killed.  If @cgrp doesn't have
	 * any css, we kick it off here.
	 */
	if (!cgrp->nr_css)
		cgroup_destroy_css_killed(cgrp);

T
Tejun Heo 已提交
4560 4561 4562
	/* remove @cgrp directory along with the base files */
	mutex_unlock(&cgroup_mutex);

4563
	/*
T
Tejun Heo 已提交
4564 4565 4566 4567 4568
	 * There are two control paths which try to determine cgroup from
	 * dentry without going through kernfs - cgroupstats_build() and
	 * css_tryget_from_dir().  Those are supported by RCU protecting
	 * clearing of cgrp->kn->priv backpointer, which should happen
	 * after all files under it have been removed.
4569
	 */
4570
	kernfs_remove(cgrp->kn);	/* @cgrp has an extra ref on its kn */
T
Tejun Heo 已提交
4571 4572
	RCU_INIT_POINTER(*(void __rcu __force **)&cgrp->kn->priv, NULL);

4573
	mutex_lock(&cgroup_mutex);
4574

4575 4576 4577
	return 0;
};

4578
/**
4579
 * cgroup_destroy_css_killed - the second step of cgroup destruction
4580 4581 4582
 * @work: cgroup->destroy_free_work
 *
 * This function is invoked from a work item for a cgroup which is being
4583 4584 4585
 * destroyed after all css's are offlined and performs the rest of
 * destruction.  This is the second step of destruction described in the
 * comment above cgroup_destroy_locked().
4586
 */
4587
static void cgroup_destroy_css_killed(struct cgroup *cgrp)
4588 4589 4590
{
	struct cgroup *parent = cgrp->parent;

T
Tejun Heo 已提交
4591
	lockdep_assert_held(&cgroup_tree_mutex);
4592
	lockdep_assert_held(&cgroup_mutex);
4593

4594
	/* delete this cgroup from parent->children */
4595
	list_del_rcu(&cgrp->sibling);
4596

4597
	cgroup_put(cgrp);
4598

4599
	set_bit(CGRP_RELEASABLE, &parent->flags);
4600
	check_for_release(parent);
4601 4602
}

T
Tejun Heo 已提交
4603
static int cgroup_rmdir(struct kernfs_node *kn)
4604
{
T
Tejun Heo 已提交
4605 4606
	struct cgroup *cgrp = kn->priv;
	int ret = 0;
4607

T
Tejun Heo 已提交
4608 4609 4610 4611 4612 4613 4614 4615
	/*
	 * This is self-destruction but @kn can't be removed while this
	 * callback is in progress.  Let's break active protection.  Once
	 * the protection is broken, @cgrp can be destroyed at any point.
	 * Pin it so that it stays accessible.
	 */
	cgroup_get(cgrp);
	kernfs_break_active_protection(kn);
4616

T
Tejun Heo 已提交
4617
	mutex_lock(&cgroup_tree_mutex);
4618
	mutex_lock(&cgroup_mutex);
4619 4620

	/*
T
Tejun Heo 已提交
4621 4622
	 * @cgrp might already have been destroyed while we're trying to
	 * grab the mutexes.
4623
	 */
T
Tejun Heo 已提交
4624 4625
	if (!cgroup_is_dead(cgrp))
		ret = cgroup_destroy_locked(cgrp);
4626

4627
	mutex_unlock(&cgroup_mutex);
T
Tejun Heo 已提交
4628
	mutex_unlock(&cgroup_tree_mutex);
4629

T
Tejun Heo 已提交
4630 4631
	kernfs_unbreak_active_protection(kn);
	cgroup_put(cgrp);
4632
	return ret;
4633 4634
}

T
Tejun Heo 已提交
4635 4636 4637 4638 4639 4640 4641 4642
static struct kernfs_syscall_ops cgroup_kf_syscall_ops = {
	.remount_fs		= cgroup_remount,
	.show_options		= cgroup_show_options,
	.mkdir			= cgroup_mkdir,
	.rmdir			= cgroup_rmdir,
	.rename			= cgroup_rename,
};

4643
static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
4644 4645
{
	struct cgroup_subsys_state *css;
D
Diego Calleja 已提交
4646 4647

	printk(KERN_INFO "Initializing cgroup subsys %s\n", ss->name);
4648

T
Tejun Heo 已提交
4649
	mutex_lock(&cgroup_tree_mutex);
4650 4651
	mutex_lock(&cgroup_mutex);

T
Tejun Heo 已提交
4652
	INIT_LIST_HEAD(&ss->cfts);
4653

4654 4655 4656
	/* Create the root cgroup state for this subsystem */
	ss->root = &cgrp_dfl_root;
	css = ss->css_alloc(cgroup_css(&cgrp_dfl_root.cgrp, ss));
4657 4658
	/* We don't handle early failures gracefully */
	BUG_ON(IS_ERR(css));
4659
	init_css(css, ss, &cgrp_dfl_root.cgrp);
4660

L
Li Zefan 已提交
4661
	/* Update the init_css_set to contain a subsys
4662
	 * pointer to this state - since the subsystem is
L
Li Zefan 已提交
4663
	 * newly registered, all tasks and hence the
4664
	 * init_css_set is in the subsystem's root cgroup. */
4665
	init_css_set.subsys[ss->id] = css;
4666 4667 4668

	need_forkexit_callback |= ss->fork || ss->exit;

L
Li Zefan 已提交
4669 4670 4671 4672 4673
	/* At system boot, before all subsystems have been
	 * registered, no tasks have been forked, so we don't
	 * need to invoke fork callbacks here. */
	BUG_ON(!list_empty(&init_task.tasks));

4674
	BUG_ON(online_css(css));
4675

4676
	cgrp_dfl_root.subsys_mask |= 1 << ss->id;
B
Ben Blum 已提交
4677 4678

	mutex_unlock(&cgroup_mutex);
T
Tejun Heo 已提交
4679
	mutex_unlock(&cgroup_tree_mutex);
B
Ben Blum 已提交
4680 4681
}

4682
/**
L
Li Zefan 已提交
4683 4684 4685 4686
 * cgroup_init_early - cgroup initialization at system boot
 *
 * Initialize cgroups at system boot, and initialize any
 * subsystems that request early init.
4687 4688 4689
 */
int __init cgroup_init_early(void)
{
T
Tejun Heo 已提交
4690 4691
	static struct cgroup_sb_opts __initdata opts =
		{ .flags = CGRP_ROOT_SANE_BEHAVIOR };
4692
	struct cgroup_subsys *ss;
4693
	int i;
4694

4695
	init_cgroup_root(&cgrp_dfl_root, &opts);
4696
	RCU_INIT_POINTER(init_task.cgroups, &init_css_set);
4697

T
Tejun Heo 已提交
4698
	for_each_subsys(ss, i) {
4699
		WARN(!ss->css_alloc || !ss->css_free || ss->name || ss->id,
4700 4701
		     "invalid cgroup_subsys %d:%s css_alloc=%p css_free=%p name:id=%d:%s\n",
		     i, cgroup_subsys_name[i], ss->css_alloc, ss->css_free,
4702
		     ss->id, ss->name);
4703 4704 4705
		WARN(strlen(cgroup_subsys_name[i]) > MAX_CGROUP_TYPE_NAMELEN,
		     "cgroup_subsys_name %s too long\n", cgroup_subsys_name[i]);

4706
		ss->id = i;
4707
		ss->name = cgroup_subsys_name[i];
4708 4709 4710 4711 4712 4713 4714 4715

		if (ss->early_init)
			cgroup_init_subsys(ss);
	}
	return 0;
}

/**
L
Li Zefan 已提交
4716 4717 4718 4719
 * cgroup_init - cgroup initialization
 *
 * Register cgroup filesystem and /proc file, and initialize
 * any subsystems that didn't request early init.
4720 4721 4722
 */
int __init cgroup_init(void)
{
4723
	struct cgroup_subsys *ss;
4724
	unsigned long key;
4725
	int ssid, err;
4726

T
Tejun Heo 已提交
4727
	BUG_ON(cgroup_init_cftypes(NULL, cgroup_base_files));
4728

4729
	mutex_lock(&cgroup_tree_mutex);
T
Tejun Heo 已提交
4730 4731
	mutex_lock(&cgroup_mutex);

4732 4733 4734 4735
	/* Add init_css_set to the hash table */
	key = css_set_hash(init_css_set.subsys);
	hash_add(css_set_table, &init_css_set.hlist, key);

4736
	BUG_ON(cgroup_setup_root(&cgrp_dfl_root, 0));
4737

T
Tejun Heo 已提交
4738
	mutex_unlock(&cgroup_mutex);
4739
	mutex_unlock(&cgroup_tree_mutex);
T
Tejun Heo 已提交
4740

4741 4742 4743 4744
	for_each_subsys(ss, ssid) {
		if (!ss->early_init)
			cgroup_init_subsys(ss);

T
Tejun Heo 已提交
4745 4746 4747
		list_add_tail(&init_css_set.e_cset_node[ssid],
			      &cgrp_dfl_root.cgrp.e_csets[ssid]);

4748 4749 4750 4751 4752 4753
		/*
		 * cftype registration needs kmalloc and can't be done
		 * during early_init.  Register base cftypes separately.
		 */
		if (ss->base_cftypes)
			WARN_ON(cgroup_add_cftypes(ss, ss->base_cftypes));
4754 4755 4756
	}

	cgroup_kobj = kobject_create_and_add("cgroup", fs_kobj);
T
Tejun Heo 已提交
4757 4758
	if (!cgroup_kobj)
		return -ENOMEM;
4759

4760
	err = register_filesystem(&cgroup_fs_type);
4761 4762
	if (err < 0) {
		kobject_put(cgroup_kobj);
T
Tejun Heo 已提交
4763
		return err;
4764
	}
4765

L
Li Zefan 已提交
4766
	proc_create("cgroups", 0, NULL, &proc_cgroupstats_operations);
T
Tejun Heo 已提交
4767
	return 0;
4768
}
4769

4770 4771 4772 4773 4774
static int __init cgroup_wq_init(void)
{
	/*
	 * There isn't much point in executing destruction path in
	 * parallel.  Good chunk is serialized with cgroup_mutex anyway.
4775
	 * Use 1 for @max_active.
4776 4777 4778 4779
	 *
	 * We would prefer to do this in cgroup_init() above, but that
	 * is called before init_workqueues(): so leave this until after.
	 */
4780
	cgroup_destroy_wq = alloc_workqueue("cgroup_destroy", 0, 1);
4781
	BUG_ON(!cgroup_destroy_wq);
4782 4783 4784 4785 4786 4787 4788 4789 4790

	/*
	 * Used to destroy pidlists and separate to serve as flush domain.
	 * Cap @max_active to 1 too.
	 */
	cgroup_pidlist_destroy_wq = alloc_workqueue("cgroup_pidlist_destroy",
						    0, 1);
	BUG_ON(!cgroup_pidlist_destroy_wq);

4791 4792 4793 4794
	return 0;
}
core_initcall(cgroup_wq_init);

4795 4796 4797 4798 4799 4800 4801
/*
 * proc_cgroup_show()
 *  - Print task's cgroup paths into seq_file, one line for each hierarchy
 *  - Used for /proc/<pid>/cgroup.
 */

/* TODO: Use a proper seq_file iterator */
4802
int proc_cgroup_show(struct seq_file *m, void *v)
4803 4804 4805
{
	struct pid *pid;
	struct task_struct *tsk;
T
Tejun Heo 已提交
4806
	char *buf, *path;
4807
	int retval;
4808
	struct cgroup_root *root;
4809 4810

	retval = -ENOMEM;
T
Tejun Heo 已提交
4811
	buf = kmalloc(PATH_MAX, GFP_KERNEL);
4812 4813 4814 4815 4816 4817 4818 4819 4820 4821 4822 4823
	if (!buf)
		goto out;

	retval = -ESRCH;
	pid = m->private;
	tsk = get_pid_task(pid, PIDTYPE_PID);
	if (!tsk)
		goto out_free;

	retval = 0;

	mutex_lock(&cgroup_mutex);
4824
	down_read(&css_set_rwsem);
4825

4826
	for_each_root(root) {
4827
		struct cgroup_subsys *ss;
4828
		struct cgroup *cgrp;
T
Tejun Heo 已提交
4829
		int ssid, count = 0;
4830

T
Tejun Heo 已提交
4831
		if (root == &cgrp_dfl_root && !cgrp_dfl_root_visible)
4832 4833
			continue;

4834
		seq_printf(m, "%d:", root->hierarchy_id);
T
Tejun Heo 已提交
4835
		for_each_subsys(ss, ssid)
4836
			if (root->subsys_mask & (1 << ssid))
T
Tejun Heo 已提交
4837
				seq_printf(m, "%s%s", count++ ? "," : "", ss->name);
4838 4839 4840
		if (strlen(root->name))
			seq_printf(m, "%sname=%s", count ? "," : "",
				   root->name);
4841
		seq_putc(m, ':');
4842
		cgrp = task_cgroup_from_root(tsk, root);
T
Tejun Heo 已提交
4843 4844 4845
		path = cgroup_path(cgrp, buf, PATH_MAX);
		if (!path) {
			retval = -ENAMETOOLONG;
4846
			goto out_unlock;
T
Tejun Heo 已提交
4847 4848
		}
		seq_puts(m, path);
4849 4850 4851 4852
		seq_putc(m, '\n');
	}

out_unlock:
4853
	up_read(&css_set_rwsem);
4854 4855 4856 4857 4858 4859 4860 4861 4862 4863 4864
	mutex_unlock(&cgroup_mutex);
	put_task_struct(tsk);
out_free:
	kfree(buf);
out:
	return retval;
}

/* Display information about each subsystem and each hierarchy */
static int proc_cgroupstats_show(struct seq_file *m, void *v)
{
4865
	struct cgroup_subsys *ss;
4866 4867
	int i;

4868
	seq_puts(m, "#subsys_name\thierarchy\tnum_cgroups\tenabled\n");
B
Ben Blum 已提交
4869 4870 4871 4872 4873
	/*
	 * ideally we don't want subsystems moving around while we do this.
	 * cgroup_mutex is also necessary to guarantee an atomic snapshot of
	 * subsys/hierarchy state.
	 */
4874
	mutex_lock(&cgroup_mutex);
4875 4876

	for_each_subsys(ss, i)
4877 4878
		seq_printf(m, "%s\t%d\t%d\t%d\n",
			   ss->name, ss->root->hierarchy_id,
4879
			   atomic_read(&ss->root->nr_cgrps), !ss->disabled);
4880

4881 4882 4883 4884 4885 4886
	mutex_unlock(&cgroup_mutex);
	return 0;
}

static int cgroupstats_open(struct inode *inode, struct file *file)
{
A
Al Viro 已提交
4887
	return single_open(file, proc_cgroupstats_show, NULL);
4888 4889
}

4890
static const struct file_operations proc_cgroupstats_operations = {
4891 4892 4893 4894 4895 4896
	.open = cgroupstats_open,
	.read = seq_read,
	.llseek = seq_lseek,
	.release = single_release,
};

4897
/**
4898
 * cgroup_fork - initialize cgroup related fields during copy_process()
L
Li Zefan 已提交
4899
 * @child: pointer to task_struct of forking parent process.
4900
 *
4901 4902 4903
 * A task is associated with the init_css_set until cgroup_post_fork()
 * attaches it to the parent's css_set.  Empty cg_list indicates that
 * @child isn't holding reference to its css_set.
4904 4905 4906
 */
void cgroup_fork(struct task_struct *child)
{
4907
	RCU_INIT_POINTER(child->cgroups, &init_css_set);
4908
	INIT_LIST_HEAD(&child->cg_list);
4909 4910
}

4911
/**
L
Li Zefan 已提交
4912 4913 4914
 * cgroup_post_fork - called on a new task after adding it to the task list
 * @child: the task in question
 *
4915 4916 4917
 * Adds the task to the list running through its css_set if necessary and
 * call the subsystem fork() callbacks.  Has to be after the task is
 * visible on the task list in case we race with the first call to
4918
 * cgroup_task_iter_start() - to guarantee that the new task ends up on its
4919
 * list.
L
Li Zefan 已提交
4920
 */
4921 4922
void cgroup_post_fork(struct task_struct *child)
{
4923
	struct cgroup_subsys *ss;
4924 4925
	int i;

4926
	/*
4927 4928 4929 4930 4931 4932 4933 4934 4935 4936 4937 4938 4939 4940 4941 4942 4943 4944 4945
	 * This may race against cgroup_enable_task_cg_links().  As that
	 * function sets use_task_css_set_links before grabbing
	 * tasklist_lock and we just went through tasklist_lock to add
	 * @child, it's guaranteed that either we see the set
	 * use_task_css_set_links or cgroup_enable_task_cg_lists() sees
	 * @child during its iteration.
	 *
	 * If we won the race, @child is associated with %current's
	 * css_set.  Grabbing css_set_rwsem guarantees both that the
	 * association is stable, and, on completion of the parent's
	 * migration, @child is visible in the source of migration or
	 * already in the destination cgroup.  This guarantee is necessary
	 * when implementing operations which need to migrate all tasks of
	 * a cgroup to another.
	 *
	 * Note that if we lose to cgroup_enable_task_cg_links(), @child
	 * will remain in init_css_set.  This is safe because all tasks are
	 * in the init_css_set before cg_links is enabled and there's no
	 * operation which transfers all tasks out of init_css_set.
4946
	 */
4947
	if (use_task_css_set_links) {
4948 4949
		struct css_set *cset;

4950
		down_write(&css_set_rwsem);
4951
		cset = task_css_set(current);
4952 4953 4954 4955 4956
		if (list_empty(&child->cg_list)) {
			rcu_assign_pointer(child->cgroups, cset);
			list_add(&child->cg_list, &cset->tasks);
			get_css_set(cset);
		}
4957
		up_write(&css_set_rwsem);
4958
	}
4959 4960 4961 4962 4963 4964 4965

	/*
	 * Call ss->fork().  This must happen after @child is linked on
	 * css_set; otherwise, @child might change state between ->fork()
	 * and addition to css_set.
	 */
	if (need_forkexit_callback) {
T
Tejun Heo 已提交
4966
		for_each_subsys(ss, i)
4967 4968 4969
			if (ss->fork)
				ss->fork(child);
	}
4970
}
4971

4972 4973 4974 4975 4976 4977 4978 4979 4980 4981 4982 4983
/**
 * cgroup_exit - detach cgroup from exiting task
 * @tsk: pointer to task_struct of exiting process
 *
 * Description: Detach cgroup from @tsk and release it.
 *
 * Note that cgroups marked notify_on_release force every task in
 * them to take the global cgroup_mutex mutex when exiting.
 * This could impact scaling on very large systems.  Be reluctant to
 * use notify_on_release cgroups where very high task exit scaling
 * is required on large systems.
 *
4984 4985 4986 4987 4988
 * We set the exiting tasks cgroup to the root cgroup (top_cgroup).  We
 * call cgroup_exit() while the task is still competent to handle
 * notify_on_release(), then leave the task attached to the root cgroup in
 * each hierarchy for the remainder of its exit.  No need to bother with
 * init_css_set refcnting.  init_css_set never goes away and we can't race
4989
 * with migration path - PF_EXITING is visible to migration path.
4990
 */
4991
void cgroup_exit(struct task_struct *tsk)
4992
{
4993
	struct cgroup_subsys *ss;
4994
	struct css_set *cset;
4995
	bool put_cset = false;
4996
	int i;
4997 4998

	/*
4999 5000
	 * Unlink from @tsk from its css_set.  As migration path can't race
	 * with us, we can check cg_list without grabbing css_set_rwsem.
5001 5002
	 */
	if (!list_empty(&tsk->cg_list)) {
5003
		down_write(&css_set_rwsem);
5004
		list_del_init(&tsk->cg_list);
5005
		up_write(&css_set_rwsem);
5006
		put_cset = true;
5007 5008
	}

5009
	/* Reassign the task to the init_css_set. */
5010 5011
	cset = task_css_set(tsk);
	RCU_INIT_POINTER(tsk->cgroups, &init_css_set);
5012

5013
	if (need_forkexit_callback) {
T
Tejun Heo 已提交
5014 5015
		/* see cgroup_post_fork() for details */
		for_each_subsys(ss, i) {
5016
			if (ss->exit) {
5017 5018
				struct cgroup_subsys_state *old_css = cset->subsys[i];
				struct cgroup_subsys_state *css = task_css(tsk, i);
5019

5020
				ss->exit(css, old_css, tsk);
5021 5022 5023 5024
			}
		}
	}

5025 5026
	if (put_cset)
		put_css_set(cset, true);
5027
}
5028

5029
static void check_for_release(struct cgroup *cgrp)
5030
{
5031
	if (cgroup_is_releasable(cgrp) &&
T
Tejun Heo 已提交
5032
	    list_empty(&cgrp->cset_links) && list_empty(&cgrp->children)) {
5033 5034
		/*
		 * Control Group is currently removeable. If it's not
5035
		 * already queued for a userspace notification, queue
5036 5037
		 * it now
		 */
5038
		int need_schedule_work = 0;
5039

5040
		raw_spin_lock(&release_list_lock);
5041
		if (!cgroup_is_dead(cgrp) &&
5042 5043
		    list_empty(&cgrp->release_list)) {
			list_add(&cgrp->release_list, &release_list);
5044 5045
			need_schedule_work = 1;
		}
5046
		raw_spin_unlock(&release_list_lock);
5047 5048 5049 5050 5051 5052 5053 5054 5055 5056 5057 5058 5059 5060 5061 5062 5063 5064 5065 5066 5067 5068 5069 5070 5071 5072 5073 5074 5075 5076 5077 5078
		if (need_schedule_work)
			schedule_work(&release_agent_work);
	}
}

/*
 * Notify userspace when a cgroup is released, by running the
 * configured release agent with the name of the cgroup (path
 * relative to the root of cgroup file system) as the argument.
 *
 * Most likely, this user command will try to rmdir this cgroup.
 *
 * This races with the possibility that some other task will be
 * attached to this cgroup before it is removed, or that some other
 * user task will 'mkdir' a child cgroup of this cgroup.  That's ok.
 * The presumed 'rmdir' will fail quietly if this cgroup is no longer
 * unused, and this cgroup will be reprieved from its death sentence,
 * to continue to serve a useful existence.  Next time it's released,
 * we will get notified again, if it still has 'notify_on_release' set.
 *
 * The final arg to call_usermodehelper() is UMH_WAIT_EXEC, which
 * means only wait until the task is successfully execve()'d.  The
 * separate release agent task is forked by call_usermodehelper(),
 * then control in this thread returns here, without waiting for the
 * release agent task.  We don't bother to wait because the caller of
 * this routine has no use for the exit status of the release agent
 * task, so no sense holding our caller up for that.
 */
static void cgroup_release_agent(struct work_struct *work)
{
	BUG_ON(work != &release_agent_work);
	mutex_lock(&cgroup_mutex);
5079
	raw_spin_lock(&release_list_lock);
5080 5081 5082
	while (!list_empty(&release_list)) {
		char *argv[3], *envp[3];
		int i;
T
Tejun Heo 已提交
5083
		char *pathbuf = NULL, *agentbuf = NULL, *path;
5084
		struct cgroup *cgrp = list_entry(release_list.next,
5085 5086
						    struct cgroup,
						    release_list);
5087
		list_del_init(&cgrp->release_list);
5088
		raw_spin_unlock(&release_list_lock);
T
Tejun Heo 已提交
5089
		pathbuf = kmalloc(PATH_MAX, GFP_KERNEL);
5090 5091
		if (!pathbuf)
			goto continue_free;
T
Tejun Heo 已提交
5092 5093
		path = cgroup_path(cgrp, pathbuf, PATH_MAX);
		if (!path)
5094 5095 5096 5097
			goto continue_free;
		agentbuf = kstrdup(cgrp->root->release_agent_path, GFP_KERNEL);
		if (!agentbuf)
			goto continue_free;
5098 5099

		i = 0;
5100
		argv[i++] = agentbuf;
T
Tejun Heo 已提交
5101
		argv[i++] = path;
5102 5103 5104 5105 5106 5107 5108 5109 5110 5111 5112 5113 5114 5115
		argv[i] = NULL;

		i = 0;
		/* minimal command environment */
		envp[i++] = "HOME=/";
		envp[i++] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
		envp[i] = NULL;

		/* Drop the lock while we invoke the usermode helper,
		 * since the exec could involve hitting disk and hence
		 * be a slow process */
		mutex_unlock(&cgroup_mutex);
		call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
		mutex_lock(&cgroup_mutex);
5116 5117 5118
 continue_free:
		kfree(pathbuf);
		kfree(agentbuf);
5119
		raw_spin_lock(&release_list_lock);
5120
	}
5121
	raw_spin_unlock(&release_list_lock);
5122 5123
	mutex_unlock(&cgroup_mutex);
}
5124 5125 5126

static int __init cgroup_disable(char *str)
{
5127
	struct cgroup_subsys *ss;
5128
	char *token;
5129
	int i;
5130 5131 5132 5133

	while ((token = strsep(&str, ",")) != NULL) {
		if (!*token)
			continue;
5134

T
Tejun Heo 已提交
5135
		for_each_subsys(ss, i) {
5136 5137 5138 5139 5140 5141 5142 5143 5144 5145 5146
			if (!strcmp(token, ss->name)) {
				ss->disabled = 1;
				printk(KERN_INFO "Disabling %s control group"
					" subsystem\n", ss->name);
				break;
			}
		}
	}
	return 1;
}
__setup("cgroup_disable=", cgroup_disable);
K
KAMEZAWA Hiroyuki 已提交
5147

5148
/**
5149
 * css_tryget_from_dir - get corresponding css from the dentry of a cgroup dir
5150 5151
 * @dentry: directory dentry of interest
 * @ss: subsystem of interest
5152
 *
5153 5154 5155
 * If @dentry is a directory for a cgroup which has @ss enabled on it, try
 * to get the corresponding css and return it.  If such css doesn't exist
 * or can't be pinned, an ERR_PTR value is returned.
S
Stephane Eranian 已提交
5156
 */
5157 5158
struct cgroup_subsys_state *css_tryget_from_dir(struct dentry *dentry,
						struct cgroup_subsys *ss)
S
Stephane Eranian 已提交
5159
{
T
Tejun Heo 已提交
5160 5161
	struct kernfs_node *kn = kernfs_node_from_dentry(dentry);
	struct cgroup_subsys_state *css = NULL;
S
Stephane Eranian 已提交
5162 5163
	struct cgroup *cgrp;

5164
	/* is @dentry a cgroup dir? */
T
Tejun Heo 已提交
5165 5166
	if (dentry->d_sb->s_type != &cgroup_fs_type || !kn ||
	    kernfs_type(kn) != KERNFS_DIR)
S
Stephane Eranian 已提交
5167 5168
		return ERR_PTR(-EBADF);

5169 5170
	rcu_read_lock();

T
Tejun Heo 已提交
5171 5172 5173 5174 5175 5176 5177 5178
	/*
	 * This path doesn't originate from kernfs and @kn could already
	 * have been or be removed at any point.  @kn->priv is RCU
	 * protected for this access.  See destroy_locked() for details.
	 */
	cgrp = rcu_dereference(kn->priv);
	if (cgrp)
		css = cgroup_css(cgrp, ss);
5179 5180 5181 5182 5183 5184

	if (!css || !css_tryget(css))
		css = ERR_PTR(-ENOENT);

	rcu_read_unlock();
	return css;
S
Stephane Eranian 已提交
5185 5186
}

5187 5188 5189 5190 5191 5192 5193 5194 5195 5196 5197 5198
/**
 * css_from_id - lookup css by id
 * @id: the cgroup id
 * @ss: cgroup subsys to be looked into
 *
 * Returns the css if there's valid one with @id, otherwise returns NULL.
 * Should be called under rcu_read_lock().
 */
struct cgroup_subsys_state *css_from_id(int id, struct cgroup_subsys *ss)
{
	struct cgroup *cgrp;

5199
	WARN_ON_ONCE(!rcu_read_lock_held());
5200 5201 5202

	cgrp = idr_find(&ss->root->cgroup_idr, id);
	if (cgrp)
5203
		return cgroup_css(cgrp, ss);
5204
	return NULL;
S
Stephane Eranian 已提交
5205 5206
}

5207
#ifdef CONFIG_CGROUP_DEBUG
5208 5209
static struct cgroup_subsys_state *
debug_css_alloc(struct cgroup_subsys_state *parent_css)
5210 5211 5212 5213 5214 5215 5216 5217 5218
{
	struct cgroup_subsys_state *css = kzalloc(sizeof(*css), GFP_KERNEL);

	if (!css)
		return ERR_PTR(-ENOMEM);

	return css;
}

5219
static void debug_css_free(struct cgroup_subsys_state *css)
5220
{
5221
	kfree(css);
5222 5223
}

5224 5225
static u64 debug_taskcount_read(struct cgroup_subsys_state *css,
				struct cftype *cft)
5226
{
5227
	return cgroup_task_count(css->cgroup);
5228 5229
}

5230 5231
static u64 current_css_set_read(struct cgroup_subsys_state *css,
				struct cftype *cft)
5232 5233 5234 5235
{
	return (u64)(unsigned long)current->cgroups;
}

5236
static u64 current_css_set_refcount_read(struct cgroup_subsys_state *css,
L
Li Zefan 已提交
5237
					 struct cftype *cft)
5238 5239 5240 5241
{
	u64 count;

	rcu_read_lock();
5242
	count = atomic_read(&task_css_set(current)->refcount);
5243 5244 5245 5246
	rcu_read_unlock();
	return count;
}

5247
static int current_css_set_cg_links_read(struct seq_file *seq, void *v)
5248
{
5249
	struct cgrp_cset_link *link;
5250
	struct css_set *cset;
T
Tejun Heo 已提交
5251 5252 5253 5254 5255
	char *name_buf;

	name_buf = kmalloc(NAME_MAX + 1, GFP_KERNEL);
	if (!name_buf)
		return -ENOMEM;
5256

5257
	down_read(&css_set_rwsem);
5258
	rcu_read_lock();
5259
	cset = rcu_dereference(current->cgroups);
5260
	list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
5261 5262
		struct cgroup *c = link->cgrp;

T
Tejun Heo 已提交
5263
		cgroup_name(c, name_buf, NAME_MAX + 1);
5264
		seq_printf(seq, "Root %d group %s\n",
T
Tejun Heo 已提交
5265
			   c->root->hierarchy_id, name_buf);
5266 5267
	}
	rcu_read_unlock();
5268
	up_read(&css_set_rwsem);
T
Tejun Heo 已提交
5269
	kfree(name_buf);
5270 5271 5272 5273
	return 0;
}

#define MAX_TASKS_SHOWN_PER_CSS 25
5274
static int cgroup_css_links_read(struct seq_file *seq, void *v)
5275
{
5276
	struct cgroup_subsys_state *css = seq_css(seq);
5277
	struct cgrp_cset_link *link;
5278

5279
	down_read(&css_set_rwsem);
5280
	list_for_each_entry(link, &css->cgroup->cset_links, cset_link) {
5281
		struct css_set *cset = link->cset;
5282 5283
		struct task_struct *task;
		int count = 0;
T
Tejun Heo 已提交
5284

5285
		seq_printf(seq, "css_set %p\n", cset);
T
Tejun Heo 已提交
5286

5287
		list_for_each_entry(task, &cset->tasks, cg_list) {
T
Tejun Heo 已提交
5288 5289 5290 5291 5292 5293 5294 5295 5296
			if (count++ > MAX_TASKS_SHOWN_PER_CSS)
				goto overflow;
			seq_printf(seq, "  task %d\n", task_pid_vnr(task));
		}

		list_for_each_entry(task, &cset->mg_tasks, cg_list) {
			if (count++ > MAX_TASKS_SHOWN_PER_CSS)
				goto overflow;
			seq_printf(seq, "  task %d\n", task_pid_vnr(task));
5297
		}
T
Tejun Heo 已提交
5298 5299 5300
		continue;
	overflow:
		seq_puts(seq, "  ...\n");
5301
	}
5302
	up_read(&css_set_rwsem);
5303 5304 5305
	return 0;
}

5306
static u64 releasable_read(struct cgroup_subsys_state *css, struct cftype *cft)
5307
{
5308
	return test_bit(CGRP_RELEASABLE, &css->cgroup->flags);
5309 5310 5311 5312 5313 5314 5315 5316 5317 5318 5319 5320 5321 5322 5323 5324 5325 5326
}

static struct cftype debug_files[] =  {
	{
		.name = "taskcount",
		.read_u64 = debug_taskcount_read,
	},

	{
		.name = "current_css_set",
		.read_u64 = current_css_set_read,
	},

	{
		.name = "current_css_set_refcount",
		.read_u64 = current_css_set_refcount_read,
	},

5327 5328
	{
		.name = "current_css_set_cg_links",
5329
		.seq_show = current_css_set_cg_links_read,
5330 5331 5332 5333
	},

	{
		.name = "cgroup_css_links",
5334
		.seq_show = cgroup_css_links_read,
5335 5336
	},

5337 5338 5339 5340 5341
	{
		.name = "releasable",
		.read_u64 = releasable_read,
	},

5342 5343
	{ }	/* terminate */
};
5344

5345
struct cgroup_subsys debug_cgrp_subsys = {
5346 5347
	.css_alloc = debug_css_alloc,
	.css_free = debug_css_free,
5348
	.base_cftypes = debug_files,
5349 5350
};
#endif /* CONFIG_CGROUP_DEBUG */