eventpoll.c 60.2 KB
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/*
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 *  fs/eventpoll.c (Efficient event retrieval implementation)
 *  Copyright (C) 2001,...,2009	 Davide Libenzi
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 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  Davide Libenzi <davidel@xmailserver.org>
 *
 */

#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/signal.h>
#include <linux/errno.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/poll.h>
#include <linux/string.h>
#include <linux/list.h>
#include <linux/hash.h>
#include <linux/spinlock.h>
#include <linux/syscalls.h>
#include <linux/rbtree.h>
#include <linux/wait.h>
#include <linux/eventpoll.h>
#include <linux/mount.h>
#include <linux/bitops.h>
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#include <linux/mutex.h>
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#include <linux/anon_inodes.h>
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#include <linux/device.h>
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#include <linux/uaccess.h>
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#include <asm/io.h>
#include <asm/mman.h>
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#include <linux/atomic.h>
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#include <linux/proc_fs.h>
#include <linux/seq_file.h>
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#include <linux/compat.h>
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#include <linux/rculist.h>
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/*
 * LOCKING:
 * There are three level of locking required by epoll :
 *
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 * 1) epmutex (mutex)
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 * 2) ep->mtx (mutex)
 * 3) ep->lock (spinlock)
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 *
 * The acquire order is the one listed above, from 1 to 3.
 * We need a spinlock (ep->lock) because we manipulate objects
 * from inside the poll callback, that might be triggered from
 * a wake_up() that in turn might be called from IRQ context.
 * So we can't sleep inside the poll callback and hence we need
 * a spinlock. During the event transfer loop (from kernel to
 * user space) we could end up sleeping due a copy_to_user(), so
 * we need a lock that will allow us to sleep. This lock is a
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 * mutex (ep->mtx). It is acquired during the event transfer loop,
 * during epoll_ctl(EPOLL_CTL_DEL) and during eventpoll_release_file().
 * Then we also need a global mutex to serialize eventpoll_release_file()
 * and ep_free().
 * This mutex is acquired by ep_free() during the epoll file
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 * cleanup path and it is also acquired by eventpoll_release_file()
 * if a file has been pushed inside an epoll set and it is then
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 * close()d without a previous call to epoll_ctl(EPOLL_CTL_DEL).
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 * It is also acquired when inserting an epoll fd onto another epoll
 * fd. We do this so that we walk the epoll tree and ensure that this
 * insertion does not create a cycle of epoll file descriptors, which
 * could lead to deadlock. We need a global mutex to prevent two
 * simultaneous inserts (A into B and B into A) from racing and
 * constructing a cycle without either insert observing that it is
 * going to.
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 * It is necessary to acquire multiple "ep->mtx"es at once in the
 * case when one epoll fd is added to another. In this case, we
 * always acquire the locks in the order of nesting (i.e. after
 * epoll_ctl(e1, EPOLL_CTL_ADD, e2), e1->mtx will always be acquired
 * before e2->mtx). Since we disallow cycles of epoll file
 * descriptors, this ensures that the mutexes are well-ordered. In
 * order to communicate this nesting to lockdep, when walking a tree
 * of epoll file descriptors, we use the current recursion depth as
 * the lockdep subkey.
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 * It is possible to drop the "ep->mtx" and to use the global
 * mutex "epmutex" (together with "ep->lock") to have it working,
 * but having "ep->mtx" will make the interface more scalable.
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 * Events that require holding "epmutex" are very rare, while for
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 * normal operations the epoll private "ep->mtx" will guarantee
 * a better scalability.
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 */

/* Epoll private bits inside the event mask */
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#define EP_PRIVATE_BITS (EPOLLWAKEUP | EPOLLONESHOT | EPOLLET | EPOLLEXCLUSIVE)
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#define EPOLLINOUT_BITS (POLLIN | POLLOUT)

#define EPOLLEXCLUSIVE_OK_BITS (EPOLLINOUT_BITS | POLLERR | POLLHUP | \
				EPOLLWAKEUP | EPOLLET | EPOLLEXCLUSIVE)

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/* Maximum number of nesting allowed inside epoll sets */
#define EP_MAX_NESTS 4
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#define EP_MAX_EVENTS (INT_MAX / sizeof(struct epoll_event))

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#define EP_UNACTIVE_PTR ((void *) -1L)

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#define EP_ITEM_COST (sizeof(struct epitem) + sizeof(struct eppoll_entry))

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struct epoll_filefd {
	struct file *file;
	int fd;
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} __packed;
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/*
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 * Structure used to track possible nested calls, for too deep recursions
 * and loop cycles.
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 */
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struct nested_call_node {
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	struct list_head llink;
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	void *cookie;
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	void *ctx;
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};

/*
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 * This structure is used as collector for nested calls, to check for
 * maximum recursion dept and loop cycles.
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 */
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struct nested_calls {
	struct list_head tasks_call_list;
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	spinlock_t lock;
};

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/*
 * Each file descriptor added to the eventpoll interface will
 * have an entry of this type linked to the "rbr" RB tree.
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 * Avoid increasing the size of this struct, there can be many thousands
 * of these on a server and we do not want this to take another cache line.
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 */
struct epitem {
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	union {
		/* RB tree node links this structure to the eventpoll RB tree */
		struct rb_node rbn;
		/* Used to free the struct epitem */
		struct rcu_head rcu;
	};
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	/* List header used to link this structure to the eventpoll ready list */
	struct list_head rdllink;

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	/*
	 * Works together "struct eventpoll"->ovflist in keeping the
	 * single linked chain of items.
	 */
	struct epitem *next;

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	/* The file descriptor information this item refers to */
	struct epoll_filefd ffd;

	/* Number of active wait queue attached to poll operations */
	int nwait;

	/* List containing poll wait queues */
	struct list_head pwqlist;

	/* The "container" of this item */
	struct eventpoll *ep;

	/* List header used to link this item to the "struct file" items list */
	struct list_head fllink;

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	/* wakeup_source used when EPOLLWAKEUP is set */
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	struct wakeup_source __rcu *ws;
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	/* The structure that describe the interested events and the source fd */
	struct epoll_event event;
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};

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/*
 * This structure is stored inside the "private_data" member of the file
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 * structure and represents the main data structure for the eventpoll
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 * interface.
 */
struct eventpoll {
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	/* Protect the access to this structure */
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	spinlock_t lock;
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	/*
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	 * This mutex is used to ensure that files are not removed
	 * while epoll is using them. This is held during the event
	 * collection loop, the file cleanup path, the epoll file exit
	 * code and the ctl operations.
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	 */
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	struct mutex mtx;
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	/* Wait queue used by sys_epoll_wait() */
	wait_queue_head_t wq;

	/* Wait queue used by file->poll() */
	wait_queue_head_t poll_wait;

	/* List of ready file descriptors */
	struct list_head rdllist;

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	/* RB tree root used to store monitored fd structs */
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	struct rb_root rbr;
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	/*
	 * This is a single linked list that chains all the "struct epitem" that
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	 * happened while transferring ready events to userspace w/out
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	 * holding ->lock.
	 */
	struct epitem *ovflist;
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	/* wakeup_source used when ep_scan_ready_list is running */
	struct wakeup_source *ws;

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	/* The user that created the eventpoll descriptor */
	struct user_struct *user;
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	struct file *file;

	/* used to optimize loop detection check */
	int visited;
	struct list_head visited_list_link;
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};

/* Wait structure used by the poll hooks */
struct eppoll_entry {
	/* List header used to link this structure to the "struct epitem" */
	struct list_head llink;

	/* The "base" pointer is set to the container "struct epitem" */
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	struct epitem *base;
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	/*
	 * Wait queue item that will be linked to the target file wait
	 * queue head.
	 */
	wait_queue_t wait;

	/* The wait queue head that linked the "wait" wait queue item */
	wait_queue_head_t *whead;
};

/* Wrapper struct used by poll queueing */
struct ep_pqueue {
	poll_table pt;
	struct epitem *epi;
};

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/* Used by the ep_send_events() function as callback private data */
struct ep_send_events_data {
	int maxevents;
	struct epoll_event __user *events;
};

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/*
 * Configuration options available inside /proc/sys/fs/epoll/
 */
/* Maximum number of epoll watched descriptors, per user */
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static long max_user_watches __read_mostly;
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/*
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 * This mutex is used to serialize ep_free() and eventpoll_release_file().
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 */
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static DEFINE_MUTEX(epmutex);
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/* Used to check for epoll file descriptor inclusion loops */
static struct nested_calls poll_loop_ncalls;

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/* Used for safe wake up implementation */
static struct nested_calls poll_safewake_ncalls;

/* Used to call file's f_op->poll() under the nested calls boundaries */
static struct nested_calls poll_readywalk_ncalls;
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/* Slab cache used to allocate "struct epitem" */
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static struct kmem_cache *epi_cache __read_mostly;
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/* Slab cache used to allocate "struct eppoll_entry" */
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static struct kmem_cache *pwq_cache __read_mostly;
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/* Visited nodes during ep_loop_check(), so we can unset them when we finish */
static LIST_HEAD(visited_list);

/*
 * List of files with newly added links, where we may need to limit the number
 * of emanating paths. Protected by the epmutex.
 */
static LIST_HEAD(tfile_check_list);

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#ifdef CONFIG_SYSCTL

#include <linux/sysctl.h>

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static long zero;
static long long_max = LONG_MAX;
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struct ctl_table epoll_table[] = {
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	{
		.procname	= "max_user_watches",
		.data		= &max_user_watches,
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		.maxlen		= sizeof(max_user_watches),
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		.mode		= 0644,
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		.proc_handler	= proc_doulongvec_minmax,
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		.extra1		= &zero,
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		.extra2		= &long_max,
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	},
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	{ }
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};
#endif /* CONFIG_SYSCTL */

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static const struct file_operations eventpoll_fops;

static inline int is_file_epoll(struct file *f)
{
	return f->f_op == &eventpoll_fops;
}
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/* Setup the structure that is used as key for the RB tree */
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static inline void ep_set_ffd(struct epoll_filefd *ffd,
			      struct file *file, int fd)
{
	ffd->file = file;
	ffd->fd = fd;
}

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/* Compare RB tree keys */
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static inline int ep_cmp_ffd(struct epoll_filefd *p1,
			     struct epoll_filefd *p2)
{
	return (p1->file > p2->file ? +1:
	        (p1->file < p2->file ? -1 : p1->fd - p2->fd));
}

/* Tells us if the item is currently linked */
static inline int ep_is_linked(struct list_head *p)
{
	return !list_empty(p);
}

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static inline struct eppoll_entry *ep_pwq_from_wait(wait_queue_t *p)
{
	return container_of(p, struct eppoll_entry, wait);
}

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/* Get the "struct epitem" from a wait queue pointer */
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static inline struct epitem *ep_item_from_wait(wait_queue_t *p)
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{
	return container_of(p, struct eppoll_entry, wait)->base;
}

/* Get the "struct epitem" from an epoll queue wrapper */
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static inline struct epitem *ep_item_from_epqueue(poll_table *p)
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{
	return container_of(p, struct ep_pqueue, pt)->epi;
}

/* Tells if the epoll_ctl(2) operation needs an event copy from userspace */
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static inline int ep_op_has_event(int op)
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{
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	return op != EPOLL_CTL_DEL;
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}

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/* Initialize the poll safe wake up structure */
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static void ep_nested_calls_init(struct nested_calls *ncalls)
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{
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	INIT_LIST_HEAD(&ncalls->tasks_call_list);
	spin_lock_init(&ncalls->lock);
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}

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/**
 * ep_events_available - Checks if ready events might be available.
 *
 * @ep: Pointer to the eventpoll context.
 *
 * Returns: Returns a value different than zero if ready events are available,
 *          or zero otherwise.
 */
static inline int ep_events_available(struct eventpoll *ep)
{
	return !list_empty(&ep->rdllist) || ep->ovflist != EP_UNACTIVE_PTR;
}

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/**
 * ep_call_nested - Perform a bound (possibly) nested call, by checking
 *                  that the recursion limit is not exceeded, and that
 *                  the same nested call (by the meaning of same cookie) is
 *                  no re-entered.
 *
 * @ncalls: Pointer to the nested_calls structure to be used for this call.
 * @max_nests: Maximum number of allowed nesting calls.
 * @nproc: Nested call core function pointer.
 * @priv: Opaque data to be passed to the @nproc callback.
 * @cookie: Cookie to be used to identify this nested call.
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 * @ctx: This instance context.
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 *
 * Returns: Returns the code returned by the @nproc callback, or -1 if
 *          the maximum recursion limit has been exceeded.
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 */
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static int ep_call_nested(struct nested_calls *ncalls, int max_nests,
			  int (*nproc)(void *, void *, int), void *priv,
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			  void *cookie, void *ctx)
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{
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	int error, call_nests = 0;
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	unsigned long flags;
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	struct list_head *lsthead = &ncalls->tasks_call_list;
	struct nested_call_node *tncur;
	struct nested_call_node tnode;
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	spin_lock_irqsave(&ncalls->lock, flags);
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	/*
	 * Try to see if the current task is already inside this wakeup call.
	 * We use a list here, since the population inside this set is always
	 * very much limited.
	 */
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	list_for_each_entry(tncur, lsthead, llink) {
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		if (tncur->ctx == ctx &&
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		    (tncur->cookie == cookie || ++call_nests > max_nests)) {
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			/*
			 * Ops ... loop detected or maximum nest level reached.
			 * We abort this wake by breaking the cycle itself.
			 */
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			error = -1;
			goto out_unlock;
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		}
	}

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	/* Add the current task and cookie to the list */
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	tnode.ctx = ctx;
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	tnode.cookie = cookie;
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	list_add(&tnode.llink, lsthead);

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	spin_unlock_irqrestore(&ncalls->lock, flags);
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	/* Call the nested function */
	error = (*nproc)(priv, cookie, call_nests);
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	/* Remove the current task from the list */
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	spin_lock_irqsave(&ncalls->lock, flags);
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	list_del(&tnode.llink);
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out_unlock:
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	spin_unlock_irqrestore(&ncalls->lock, flags);

	return error;
}

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/*
 * As described in commit 0ccf831cb lockdep: annotate epoll
 * the use of wait queues used by epoll is done in a very controlled
 * manner. Wake ups can nest inside each other, but are never done
 * with the same locking. For example:
 *
 *   dfd = socket(...);
 *   efd1 = epoll_create();
 *   efd2 = epoll_create();
 *   epoll_ctl(efd1, EPOLL_CTL_ADD, dfd, ...);
 *   epoll_ctl(efd2, EPOLL_CTL_ADD, efd1, ...);
 *
 * When a packet arrives to the device underneath "dfd", the net code will
 * issue a wake_up() on its poll wake list. Epoll (efd1) has installed a
 * callback wakeup entry on that queue, and the wake_up() performed by the
 * "dfd" net code will end up in ep_poll_callback(). At this point epoll
 * (efd1) notices that it may have some event ready, so it needs to wake up
 * the waiters on its poll wait list (efd2). So it calls ep_poll_safewake()
 * that ends up in another wake_up(), after having checked about the
 * recursion constraints. That are, no more than EP_MAX_POLLWAKE_NESTS, to
 * avoid stack blasting.
 *
 * When CONFIG_DEBUG_LOCK_ALLOC is enabled, make sure lockdep can handle
 * this special case of epoll.
 */
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
static inline void ep_wake_up_nested(wait_queue_head_t *wqueue,
				     unsigned long events, int subclass)
{
	unsigned long flags;

	spin_lock_irqsave_nested(&wqueue->lock, flags, subclass);
	wake_up_locked_poll(wqueue, events);
	spin_unlock_irqrestore(&wqueue->lock, flags);
}
#else
static inline void ep_wake_up_nested(wait_queue_head_t *wqueue,
				     unsigned long events, int subclass)
{
	wake_up_poll(wqueue, events);
}
#endif

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static int ep_poll_wakeup_proc(void *priv, void *cookie, int call_nests)
{
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	ep_wake_up_nested((wait_queue_head_t *) cookie, POLLIN,
			  1 + call_nests);
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	return 0;
}

/*
 * Perform a safe wake up of the poll wait list. The problem is that
 * with the new callback'd wake up system, it is possible that the
 * poll callback is reentered from inside the call to wake_up() done
 * on the poll wait queue head. The rule is that we cannot reenter the
 * wake up code from the same task more than EP_MAX_NESTS times,
 * and we cannot reenter the same wait queue head at all. This will
 * enable to have a hierarchy of epoll file descriptor of no more than
 * EP_MAX_NESTS deep.
 */
static void ep_poll_safewake(wait_queue_head_t *wq)
{
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	int this_cpu = get_cpu();

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	ep_call_nested(&poll_safewake_ncalls, EP_MAX_NESTS,
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		       ep_poll_wakeup_proc, NULL, wq, (void *) (long) this_cpu);

	put_cpu();
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}

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static void ep_remove_wait_queue(struct eppoll_entry *pwq)
{
	wait_queue_head_t *whead;

	rcu_read_lock();
	/* If it is cleared by POLLFREE, it should be rcu-safe */
	whead = rcu_dereference(pwq->whead);
	if (whead)
		remove_wait_queue(whead, &pwq->wait);
	rcu_read_unlock();
}

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/*
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 * This function unregisters poll callbacks from the associated file
 * descriptor.  Must be called with "mtx" held (or "epmutex" if called from
 * ep_free).
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 */
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static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi)
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{
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	struct list_head *lsthead = &epi->pwqlist;
	struct eppoll_entry *pwq;
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	while (!list_empty(lsthead)) {
		pwq = list_first_entry(lsthead, struct eppoll_entry, llink);
L
Linus Torvalds 已提交
545

T
Tony Battersby 已提交
546
		list_del(&pwq->llink);
547
		ep_remove_wait_queue(pwq);
T
Tony Battersby 已提交
548
		kmem_cache_free(pwq_cache, pwq);
L
Linus Torvalds 已提交
549 550 551
	}
}

552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583
/* call only when ep->mtx is held */
static inline struct wakeup_source *ep_wakeup_source(struct epitem *epi)
{
	return rcu_dereference_check(epi->ws, lockdep_is_held(&epi->ep->mtx));
}

/* call only when ep->mtx is held */
static inline void ep_pm_stay_awake(struct epitem *epi)
{
	struct wakeup_source *ws = ep_wakeup_source(epi);

	if (ws)
		__pm_stay_awake(ws);
}

static inline bool ep_has_wakeup_source(struct epitem *epi)
{
	return rcu_access_pointer(epi->ws) ? true : false;
}

/* call when ep->mtx cannot be held (ep_poll_callback) */
static inline void ep_pm_stay_awake_rcu(struct epitem *epi)
{
	struct wakeup_source *ws;

	rcu_read_lock();
	ws = rcu_dereference(epi->ws);
	if (ws)
		__pm_stay_awake(ws);
	rcu_read_unlock();
}

D
Davide Libenzi 已提交
584 585 586 587 588 589 590 591
/**
 * ep_scan_ready_list - Scans the ready list in a way that makes possible for
 *                      the scan code, to call f_op->poll(). Also allows for
 *                      O(NumReady) performance.
 *
 * @ep: Pointer to the epoll private data structure.
 * @sproc: Pointer to the scan callback.
 * @priv: Private opaque data passed to the @sproc callback.
592
 * @depth: The current depth of recursive f_op->poll calls.
593
 * @ep_locked: caller already holds ep->mtx
D
Davide Libenzi 已提交
594 595 596 597 598 599
 *
 * Returns: The same integer error code returned by the @sproc callback.
 */
static int ep_scan_ready_list(struct eventpoll *ep,
			      int (*sproc)(struct eventpoll *,
					   struct list_head *, void *),
600
			      void *priv, int depth, bool ep_locked)
D
Davide Libenzi 已提交
601 602 603 604
{
	int error, pwake = 0;
	unsigned long flags;
	struct epitem *epi, *nepi;
605
	LIST_HEAD(txlist);
D
Davide Libenzi 已提交
606 607 608

	/*
	 * We need to lock this because we could be hit by
T
Tony Battersby 已提交
609
	 * eventpoll_release_file() and epoll_ctl().
D
Davide Libenzi 已提交
610
	 */
611 612 613

	if (!ep_locked)
		mutex_lock_nested(&ep->mtx, depth);
D
Davide Libenzi 已提交
614 615 616 617 618 619 620 621 622 623

	/*
	 * Steal the ready list, and re-init the original one to the
	 * empty list. Also, set ep->ovflist to NULL so that events
	 * happening while looping w/out locks, are not lost. We cannot
	 * have the poll callback to queue directly on ep->rdllist,
	 * because we want the "sproc" callback to be able to do it
	 * in a lockless way.
	 */
	spin_lock_irqsave(&ep->lock, flags);
624
	list_splice_init(&ep->rdllist, &txlist);
D
Davide Libenzi 已提交
625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646
	ep->ovflist = NULL;
	spin_unlock_irqrestore(&ep->lock, flags);

	/*
	 * Now call the callback function.
	 */
	error = (*sproc)(ep, &txlist, priv);

	spin_lock_irqsave(&ep->lock, flags);
	/*
	 * During the time we spent inside the "sproc" callback, some
	 * other events might have been queued by the poll callback.
	 * We re-insert them inside the main ready-list here.
	 */
	for (nepi = ep->ovflist; (epi = nepi) != NULL;
	     nepi = epi->next, epi->next = EP_UNACTIVE_PTR) {
		/*
		 * We need to check if the item is already in the list.
		 * During the "sproc" callback execution time, items are
		 * queued into ->ovflist but the "txlist" might already
		 * contain them, and the list_splice() below takes care of them.
		 */
647
		if (!ep_is_linked(&epi->rdllink)) {
D
Davide Libenzi 已提交
648
			list_add_tail(&epi->rdllink, &ep->rdllist);
649
			ep_pm_stay_awake(epi);
650
		}
D
Davide Libenzi 已提交
651 652 653 654 655 656 657 658 659 660 661 662
	}
	/*
	 * We need to set back ep->ovflist to EP_UNACTIVE_PTR, so that after
	 * releasing the lock, events will be queued in the normal way inside
	 * ep->rdllist.
	 */
	ep->ovflist = EP_UNACTIVE_PTR;

	/*
	 * Quickly re-inject items left on "txlist".
	 */
	list_splice(&txlist, &ep->rdllist);
663
	__pm_relax(ep->ws);
D
Davide Libenzi 已提交
664 665 666

	if (!list_empty(&ep->rdllist)) {
		/*
667 668
		 * Wake up (if active) both the eventpoll wait list and
		 * the ->poll() wait list (delayed after we release the lock).
D
Davide Libenzi 已提交
669 670 671 672 673 674 675 676
		 */
		if (waitqueue_active(&ep->wq))
			wake_up_locked(&ep->wq);
		if (waitqueue_active(&ep->poll_wait))
			pwake++;
	}
	spin_unlock_irqrestore(&ep->lock, flags);

677 678
	if (!ep_locked)
		mutex_unlock(&ep->mtx);
D
Davide Libenzi 已提交
679 680 681 682 683 684 685 686

	/* We have to call this outside the lock */
	if (pwake)
		ep_poll_safewake(&ep->poll_wait);

	return error;
}

687 688 689 690 691 692
static void epi_rcu_free(struct rcu_head *head)
{
	struct epitem *epi = container_of(head, struct epitem, rcu);
	kmem_cache_free(epi_cache, epi);
}

693 694
/*
 * Removes a "struct epitem" from the eventpoll RB tree and deallocates
695
 * all the associated resources. Must be called with "mtx" held.
696 697 698 699 700
 */
static int ep_remove(struct eventpoll *ep, struct epitem *epi)
{
	unsigned long flags;
	struct file *file = epi->ffd.file;
L
Linus Torvalds 已提交
701 702

	/*
703 704 705 706 707 708
	 * Removes poll wait queue hooks. We _have_ to do this without holding
	 * the "ep->lock" otherwise a deadlock might occur. This because of the
	 * sequence of the lock acquisition. Here we do "ep->lock" then the wait
	 * queue head lock when unregistering the wait queue. The wakeup callback
	 * will run by holding the wait queue head lock and will call our callback
	 * that will try to get "ep->lock".
L
Linus Torvalds 已提交
709
	 */
710
	ep_unregister_pollwait(ep, epi);
L
Linus Torvalds 已提交
711

712
	/* Remove the current item from the list of epoll hooks */
J
Jonathan Corbet 已提交
713
	spin_lock(&file->f_lock);
714
	list_del_rcu(&epi->fllink);
J
Jonathan Corbet 已提交
715
	spin_unlock(&file->f_lock);
L
Linus Torvalds 已提交
716

D
Davide Libenzi 已提交
717
	rb_erase(&epi->rbn, &ep->rbr);
L
Linus Torvalds 已提交
718

719 720 721 722
	spin_lock_irqsave(&ep->lock, flags);
	if (ep_is_linked(&epi->rdllink))
		list_del_init(&epi->rdllink);
	spin_unlock_irqrestore(&ep->lock, flags);
L
Linus Torvalds 已提交
723

724
	wakeup_source_unregister(ep_wakeup_source(epi));
725 726 727 728 729 730 731 732
	/*
	 * At this point it is safe to free the eventpoll item. Use the union
	 * field epi->rcu, since we are trying to minimize the size of
	 * 'struct epitem'. The 'rbn' field is no longer in use. Protected by
	 * ep->mtx. The rcu read side, reverse_path_check_proc(), does not make
	 * use of the rbn field.
	 */
	call_rcu(&epi->rcu, epi_rcu_free);
L
Linus Torvalds 已提交
733

734
	atomic_long_dec(&ep->user->epoll_watches);
735

736
	return 0;
L
Linus Torvalds 已提交
737 738
}

739
static void ep_free(struct eventpoll *ep)
L
Linus Torvalds 已提交
740
{
741 742
	struct rb_node *rbp;
	struct epitem *epi;
L
Linus Torvalds 已提交
743

744 745
	/* We need to release all tasks waiting for these file */
	if (waitqueue_active(&ep->poll_wait))
D
Davide Libenzi 已提交
746
		ep_poll_safewake(&ep->poll_wait);
L
Linus Torvalds 已提交
747

748 749 750
	/*
	 * We need to lock this because we could be hit by
	 * eventpoll_release_file() while we're freeing the "struct eventpoll".
751
	 * We do not need to hold "ep->mtx" here because the epoll file
752 753
	 * is on the way to be removed and no one has references to it
	 * anymore. The only hit might come from eventpoll_release_file() but
L
Lucas De Marchi 已提交
754
	 * holding "epmutex" is sufficient here.
755 756
	 */
	mutex_lock(&epmutex);
L
Linus Torvalds 已提交
757 758

	/*
759
	 * Walks through the whole tree by unregistering poll callbacks.
L
Linus Torvalds 已提交
760
	 */
761 762 763 764
	for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) {
		epi = rb_entry(rbp, struct epitem, rbn);

		ep_unregister_pollwait(ep, epi);
765
		cond_resched();
766
	}
L
Linus Torvalds 已提交
767 768

	/*
769 770
	 * Walks through the whole tree by freeing each "struct epitem". At this
	 * point we are sure no poll callbacks will be lingering around, and also by
771
	 * holding "epmutex" we can be sure that no file cleanup code will hit
772
	 * us during this operation. So we can avoid the lock on "ep->lock".
773 774
	 * We do not need to lock ep->mtx, either, we only do it to prevent
	 * a lockdep warning.
L
Linus Torvalds 已提交
775
	 */
776
	mutex_lock(&ep->mtx);
777
	while ((rbp = rb_first(&ep->rbr)) != NULL) {
778 779
		epi = rb_entry(rbp, struct epitem, rbn);
		ep_remove(ep, epi);
780
		cond_resched();
781
	}
782
	mutex_unlock(&ep->mtx);
L
Linus Torvalds 已提交
783

784
	mutex_unlock(&epmutex);
785
	mutex_destroy(&ep->mtx);
786
	free_uid(ep->user);
787
	wakeup_source_unregister(ep->ws);
788
	kfree(ep);
789
}
L
Linus Torvalds 已提交
790

791 792 793
static int ep_eventpoll_release(struct inode *inode, struct file *file)
{
	struct eventpoll *ep = file->private_data;
L
Linus Torvalds 已提交
794

795
	if (ep)
796 797 798
		ep_free(ep);

	return 0;
L
Linus Torvalds 已提交
799 800
}

801 802 803 804 805 806 807
static inline unsigned int ep_item_poll(struct epitem *epi, poll_table *pt)
{
	pt->_key = epi->event.events;

	return epi->ffd.file->f_op->poll(epi->ffd.file, pt) & epi->event.events;
}

808 809
static int ep_read_events_proc(struct eventpoll *ep, struct list_head *head,
			       void *priv)
D
Davide Libenzi 已提交
810 811
{
	struct epitem *epi, *tmp;
812
	poll_table pt;
D
Davide Libenzi 已提交
813

814
	init_poll_funcptr(&pt, NULL);
815

D
Davide Libenzi 已提交
816
	list_for_each_entry_safe(epi, tmp, head, rdllink) {
817
		if (ep_item_poll(epi, &pt))
D
Davide Libenzi 已提交
818
			return POLLIN | POLLRDNORM;
819
		else {
D
Davide Libenzi 已提交
820 821 822 823 824
			/*
			 * Item has been dropped into the ready list by the poll
			 * callback, but it's not actually ready, as far as
			 * caller requested events goes. We can remove it here.
			 */
825
			__pm_relax(ep_wakeup_source(epi));
D
Davide Libenzi 已提交
826
			list_del_init(&epi->rdllink);
827
		}
D
Davide Libenzi 已提交
828 829 830 831 832
	}

	return 0;
}

833 834 835 836 837 838 839 840
static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead,
				 poll_table *pt);

struct readyevents_arg {
	struct eventpoll *ep;
	bool locked;
};

D
Davide Libenzi 已提交
841 842
static int ep_poll_readyevents_proc(void *priv, void *cookie, int call_nests)
{
843 844 845 846
	struct readyevents_arg *arg = priv;

	return ep_scan_ready_list(arg->ep, ep_read_events_proc, NULL,
				  call_nests + 1, arg->locked);
D
Davide Libenzi 已提交
847 848
}

849 850
static unsigned int ep_eventpoll_poll(struct file *file, poll_table *wait)
{
D
Davide Libenzi 已提交
851
	int pollflags;
852
	struct eventpoll *ep = file->private_data;
853 854 855 856 857 858 859 860
	struct readyevents_arg arg;

	/*
	 * During ep_insert() we already hold the ep->mtx for the tfile.
	 * Prevent re-aquisition.
	 */
	arg.locked = wait && (wait->_qproc == ep_ptable_queue_proc);
	arg.ep = ep;
L
Linus Torvalds 已提交
861

862 863 864
	/* Insert inside our poll wait queue */
	poll_wait(file, &ep->poll_wait, wait);

D
Davide Libenzi 已提交
865 866 867 868 869 870 871
	/*
	 * Proceed to find out if wanted events are really available inside
	 * the ready list. This need to be done under ep_call_nested()
	 * supervision, since the call to f_op->poll() done on listed files
	 * could re-enter here.
	 */
	pollflags = ep_call_nested(&poll_readywalk_ncalls, EP_MAX_NESTS,
872
				   ep_poll_readyevents_proc, &arg, ep, current);
873

874
	return pollflags != -1 ? pollflags : 0;
875 876
}

877
#ifdef CONFIG_PROC_FS
878
static void ep_show_fdinfo(struct seq_file *m, struct file *f)
879 880 881 882 883 884 885 886
{
	struct eventpoll *ep = f->private_data;
	struct rb_node *rbp;

	mutex_lock(&ep->mtx);
	for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) {
		struct epitem *epi = rb_entry(rbp, struct epitem, rbn);

887 888 889 890
		seq_printf(m, "tfd: %8d events: %8x data: %16llx\n",
			   epi->ffd.fd, epi->event.events,
			   (long long)epi->event.data);
		if (seq_has_overflowed(m))
891 892 893 894 895 896
			break;
	}
	mutex_unlock(&ep->mtx);
}
#endif

897 898
/* File callbacks that implement the eventpoll file behaviour */
static const struct file_operations eventpoll_fops = {
899 900 901
#ifdef CONFIG_PROC_FS
	.show_fdinfo	= ep_show_fdinfo,
#endif
902
	.release	= ep_eventpoll_release,
903 904
	.poll		= ep_eventpoll_poll,
	.llseek		= noop_llseek,
905 906
};

D
Davide Libenzi 已提交
907
/*
908 909 910
 * This is called from eventpoll_release() to unlink files from the eventpoll
 * interface. We need to have this facility to cleanup correctly files that are
 * closed without being removed from the eventpoll interface.
D
Davide Libenzi 已提交
911
 */
912
void eventpoll_release_file(struct file *file)
D
Davide Libenzi 已提交
913
{
914
	struct eventpoll *ep;
915
	struct epitem *epi, *next;
D
Davide Libenzi 已提交
916 917

	/*
J
Jonathan Corbet 已提交
918
	 * We don't want to get "file->f_lock" because it is not
919
	 * necessary. It is not necessary because we're in the "struct file"
L
Lucas De Marchi 已提交
920
	 * cleanup path, and this means that no one is using this file anymore.
D
Davide Libenzi 已提交
921
	 * So, for example, epoll_ctl() cannot hit here since if we reach this
D
Davide Libenzi 已提交
922
	 * point, the file counter already went to zero and fget() would fail.
923
	 * The only hit might come from ep_free() but by holding the mutex
924
	 * will correctly serialize the operation. We do need to acquire
925
	 * "ep->mtx" after "epmutex" because ep_remove() requires it when called
926
	 * from anywhere but ep_free().
J
Jonathan Corbet 已提交
927 928
	 *
	 * Besides, ep_remove() acquires the lock, so we can't hold it here.
D
Davide Libenzi 已提交
929
	 */
930
	mutex_lock(&epmutex);
931
	list_for_each_entry_safe(epi, next, &file->f_ep_links, fllink) {
932
		ep = epi->ep;
933
		mutex_lock_nested(&ep->mtx, 0);
934
		ep_remove(ep, epi);
935
		mutex_unlock(&ep->mtx);
D
Davide Libenzi 已提交
936
	}
937
	mutex_unlock(&epmutex);
D
Davide Libenzi 已提交
938 939
}

940
static int ep_alloc(struct eventpoll **pep)
L
Linus Torvalds 已提交
941
{
942 943 944
	int error;
	struct user_struct *user;
	struct eventpoll *ep;
L
Linus Torvalds 已提交
945

946 947 948 949 950
	user = get_current_user();
	error = -ENOMEM;
	ep = kzalloc(sizeof(*ep), GFP_KERNEL);
	if (unlikely(!ep))
		goto free_uid;
L
Linus Torvalds 已提交
951

952
	spin_lock_init(&ep->lock);
953
	mutex_init(&ep->mtx);
L
Linus Torvalds 已提交
954 955 956 957
	init_waitqueue_head(&ep->wq);
	init_waitqueue_head(&ep->poll_wait);
	INIT_LIST_HEAD(&ep->rdllist);
	ep->rbr = RB_ROOT;
958
	ep->ovflist = EP_UNACTIVE_PTR;
959
	ep->user = user;
L
Linus Torvalds 已提交
960

961
	*pep = ep;
L
Linus Torvalds 已提交
962 963

	return 0;
964 965 966 967

free_uid:
	free_uid(user);
	return error;
L
Linus Torvalds 已提交
968 969 970
}

/*
971 972 973
 * Search the file inside the eventpoll tree. The RB tree operations
 * are protected by the "mtx" mutex, and ep_find() must be called with
 * "mtx" held.
L
Linus Torvalds 已提交
974 975 976 977 978 979 980 981
 */
static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd)
{
	int kcmp;
	struct rb_node *rbp;
	struct epitem *epi, *epir = NULL;
	struct epoll_filefd ffd;

982
	ep_set_ffd(&ffd, file, fd);
L
Linus Torvalds 已提交
983 984
	for (rbp = ep->rbr.rb_node; rbp; ) {
		epi = rb_entry(rbp, struct epitem, rbn);
985
		kcmp = ep_cmp_ffd(&ffd, &epi->ffd);
L
Linus Torvalds 已提交
986 987 988 989 990 991 992 993 994 995 996 997 998 999
		if (kcmp > 0)
			rbp = rbp->rb_right;
		else if (kcmp < 0)
			rbp = rbp->rb_left;
		else {
			epir = epi;
			break;
		}
	}

	return epir;
}

/*
1000
 * This is the callback that is passed to the wait queue wakeup
D
Daniel Baluta 已提交
1001
 * mechanism. It is called by the stored file descriptors when they
1002
 * have events to report.
L
Linus Torvalds 已提交
1003
 */
1004
static int ep_poll_callback(wait_queue_t *wait, unsigned mode, int sync, void *key)
L
Linus Torvalds 已提交
1005
{
1006 1007 1008 1009
	int pwake = 0;
	unsigned long flags;
	struct epitem *epi = ep_item_from_wait(wait);
	struct eventpoll *ep = epi->ep;
J
Jason Baron 已提交
1010
	int ewake = 0;
L
Linus Torvalds 已提交
1011

1012 1013 1014 1015 1016 1017 1018 1019
	if ((unsigned long)key & POLLFREE) {
		ep_pwq_from_wait(wait)->whead = NULL;
		/*
		 * whead = NULL above can race with ep_remove_wait_queue()
		 * which can do another remove_wait_queue() after us, so we
		 * can't use __remove_wait_queue(). whead->lock is held by
		 * the caller.
		 */
1020
		list_del_init(&wait->task_list);
1021
	}
1022

1023
	spin_lock_irqsave(&ep->lock, flags);
L
Linus Torvalds 已提交
1024

1025 1026 1027 1028 1029 1030 1031
	/*
	 * If the event mask does not contain any poll(2) event, we consider the
	 * descriptor to be disabled. This condition is likely the effect of the
	 * EPOLLONESHOT bit that disables the descriptor when an event is received,
	 * until the next EPOLL_CTL_MOD will be issued.
	 */
	if (!(epi->event.events & ~EP_PRIVATE_BITS))
1032 1033
		goto out_unlock;

1034 1035 1036 1037 1038 1039 1040 1041 1042
	/*
	 * Check the events coming with the callback. At this stage, not
	 * every device reports the events in the "key" parameter of the
	 * callback. We need to be able to handle both cases here, hence the
	 * test for "key" != NULL before the event match test.
	 */
	if (key && !((unsigned long) key & epi->event.events))
		goto out_unlock;

1043
	/*
D
Daniel Baluta 已提交
1044
	 * If we are transferring events to userspace, we can hold no locks
1045
	 * (because we're accessing user memory, and because of linux f_op->poll()
D
Daniel Baluta 已提交
1046
	 * semantics). All the events that happen during that period of time are
1047 1048 1049 1050 1051 1052
	 * chained in ep->ovflist and requeued later on.
	 */
	if (unlikely(ep->ovflist != EP_UNACTIVE_PTR)) {
		if (epi->next == EP_UNACTIVE_PTR) {
			epi->next = ep->ovflist;
			ep->ovflist = epi;
1053 1054 1055 1056 1057 1058 1059 1060
			if (epi->ws) {
				/*
				 * Activate ep->ws since epi->ws may get
				 * deactivated at any time.
				 */
				__pm_stay_awake(ep->ws);
			}

1061 1062 1063
		}
		goto out_unlock;
	}
L
Linus Torvalds 已提交
1064

1065
	/* If this file is already in the ready list we exit soon */
1066
	if (!ep_is_linked(&epi->rdllink)) {
D
Davide Libenzi 已提交
1067
		list_add_tail(&epi->rdllink, &ep->rdllist);
1068
		ep_pm_stay_awake_rcu(epi);
1069
	}
1070 1071 1072 1073 1074

	/*
	 * Wake up ( if active ) both the eventpoll wait list and the ->poll()
	 * wait list.
	 */
J
Jason Baron 已提交
1075
	if (waitqueue_active(&ep->wq)) {
1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091
		if ((epi->event.events & EPOLLEXCLUSIVE) &&
					!((unsigned long)key & POLLFREE)) {
			switch ((unsigned long)key & EPOLLINOUT_BITS) {
			case POLLIN:
				if (epi->event.events & POLLIN)
					ewake = 1;
				break;
			case POLLOUT:
				if (epi->event.events & POLLOUT)
					ewake = 1;
				break;
			case 0:
				ewake = 1;
				break;
			}
		}
M
Matthew Wilcox 已提交
1092
		wake_up_locked(&ep->wq);
J
Jason Baron 已提交
1093
	}
1094 1095 1096
	if (waitqueue_active(&ep->poll_wait))
		pwake++;

1097
out_unlock:
1098
	spin_unlock_irqrestore(&ep->lock, flags);
L
Linus Torvalds 已提交
1099

1100 1101
	/* We have to call this outside the lock */
	if (pwake)
D
Davide Libenzi 已提交
1102
		ep_poll_safewake(&ep->poll_wait);
1103

J
Jason Baron 已提交
1104 1105 1106
	if (epi->event.events & EPOLLEXCLUSIVE)
		return ewake;

1107 1108
	return 1;
}
L
Linus Torvalds 已提交
1109 1110 1111 1112 1113 1114 1115 1116

/*
 * This is the callback that is used to add our wait queue to the
 * target file wakeup lists.
 */
static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead,
				 poll_table *pt)
{
1117
	struct epitem *epi = ep_item_from_epqueue(pt);
L
Linus Torvalds 已提交
1118 1119
	struct eppoll_entry *pwq;

1120
	if (epi->nwait >= 0 && (pwq = kmem_cache_alloc(pwq_cache, GFP_KERNEL))) {
L
Linus Torvalds 已提交
1121 1122 1123
		init_waitqueue_func_entry(&pwq->wait, ep_poll_callback);
		pwq->whead = whead;
		pwq->base = epi;
J
Jason Baron 已提交
1124 1125 1126 1127
		if (epi->event.events & EPOLLEXCLUSIVE)
			add_wait_queue_exclusive(whead, &pwq->wait);
		else
			add_wait_queue(whead, &pwq->wait);
L
Linus Torvalds 已提交
1128 1129
		list_add_tail(&pwq->llink, &epi->pwqlist);
		epi->nwait++;
1130
	} else {
L
Linus Torvalds 已提交
1131 1132
		/* We have to signal that an error occurred */
		epi->nwait = -1;
1133
	}
L
Linus Torvalds 已提交
1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144
}

static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi)
{
	int kcmp;
	struct rb_node **p = &ep->rbr.rb_node, *parent = NULL;
	struct epitem *epic;

	while (*p) {
		parent = *p;
		epic = rb_entry(parent, struct epitem, rbn);
1145
		kcmp = ep_cmp_ffd(&epi->ffd, &epic->ffd);
L
Linus Torvalds 已提交
1146 1147 1148 1149 1150 1151 1152 1153 1154
		if (kcmp > 0)
			p = &parent->rb_right;
		else
			p = &parent->rb_left;
	}
	rb_link_node(&epi->rbn, parent, p);
	rb_insert_color(&epi->rbn, &ep->rbr);
}

1155 1156


J
Jason Baron 已提交
1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173
#define PATH_ARR_SIZE 5
/*
 * These are the number paths of length 1 to 5, that we are allowing to emanate
 * from a single file of interest. For example, we allow 1000 paths of length
 * 1, to emanate from each file of interest. This essentially represents the
 * potential wakeup paths, which need to be limited in order to avoid massive
 * uncontrolled wakeup storms. The common use case should be a single ep which
 * is connected to n file sources. In this case each file source has 1 path
 * of length 1. Thus, the numbers below should be more than sufficient. These
 * path limits are enforced during an EPOLL_CTL_ADD operation, since a modify
 * and delete can't add additional paths. Protected by the epmutex.
 */
static const int path_limits[PATH_ARR_SIZE] = { 1000, 500, 100, 50, 10 };
static int path_count[PATH_ARR_SIZE];

static int path_count_inc(int nests)
{
J
Jason Baron 已提交
1174 1175 1176 1177
	/* Allow an arbitrary number of depth 1 paths */
	if (nests == 0)
		return 0;

J
Jason Baron 已提交
1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197
	if (++path_count[nests] > path_limits[nests])
		return -1;
	return 0;
}

static void path_count_init(void)
{
	int i;

	for (i = 0; i < PATH_ARR_SIZE; i++)
		path_count[i] = 0;
}

static int reverse_path_check_proc(void *priv, void *cookie, int call_nests)
{
	int error = 0;
	struct file *file = priv;
	struct file *child_file;
	struct epitem *epi;

1198 1199 1200
	/* CTL_DEL can remove links here, but that can't increase our count */
	rcu_read_lock();
	list_for_each_entry_rcu(epi, &file->f_ep_links, fllink) {
J
Jason Baron 已提交
1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221
		child_file = epi->ep->file;
		if (is_file_epoll(child_file)) {
			if (list_empty(&child_file->f_ep_links)) {
				if (path_count_inc(call_nests)) {
					error = -1;
					break;
				}
			} else {
				error = ep_call_nested(&poll_loop_ncalls,
							EP_MAX_NESTS,
							reverse_path_check_proc,
							child_file, child_file,
							current);
			}
			if (error != 0)
				break;
		} else {
			printk(KERN_ERR "reverse_path_check_proc: "
				"file is not an ep!\n");
		}
	}
1222
	rcu_read_unlock();
J
Jason Baron 已提交
1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252
	return error;
}

/**
 * reverse_path_check - The tfile_check_list is list of file *, which have
 *                      links that are proposed to be newly added. We need to
 *                      make sure that those added links don't add too many
 *                      paths such that we will spend all our time waking up
 *                      eventpoll objects.
 *
 * Returns: Returns zero if the proposed links don't create too many paths,
 *	    -1 otherwise.
 */
static int reverse_path_check(void)
{
	int error = 0;
	struct file *current_file;

	/* let's call this for all tfiles */
	list_for_each_entry(current_file, &tfile_check_list, f_tfile_llink) {
		path_count_init();
		error = ep_call_nested(&poll_loop_ncalls, EP_MAX_NESTS,
					reverse_path_check_proc, current_file,
					current_file, current);
		if (error)
			break;
	}
	return error;
}

1253 1254 1255
static int ep_create_wakeup_source(struct epitem *epi)
{
	const char *name;
1256
	struct wakeup_source *ws;
1257 1258 1259 1260 1261 1262 1263 1264

	if (!epi->ep->ws) {
		epi->ep->ws = wakeup_source_register("eventpoll");
		if (!epi->ep->ws)
			return -ENOMEM;
	}

	name = epi->ffd.file->f_path.dentry->d_name.name;
1265 1266 1267
	ws = wakeup_source_register(name);

	if (!ws)
1268
		return -ENOMEM;
1269
	rcu_assign_pointer(epi->ws, ws);
1270 1271 1272 1273

	return 0;
}

1274 1275
/* rare code path, only used when EPOLL_CTL_MOD removes a wakeup source */
static noinline void ep_destroy_wakeup_source(struct epitem *epi)
1276
{
1277 1278
	struct wakeup_source *ws = ep_wakeup_source(epi);

1279
	RCU_INIT_POINTER(epi->ws, NULL);
1280 1281 1282 1283 1284 1285 1286 1287

	/*
	 * wait for ep_pm_stay_awake_rcu to finish, synchronize_rcu is
	 * used internally by wakeup_source_remove, too (called by
	 * wakeup_source_unregister), so we cannot use call_rcu
	 */
	synchronize_rcu();
	wakeup_source_unregister(ws);
1288 1289
}

1290 1291 1292
/*
 * Must be called with "mtx" held.
 */
L
Linus Torvalds 已提交
1293
static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
1294
		     struct file *tfile, int fd, int full_check)
L
Linus Torvalds 已提交
1295 1296 1297
{
	int error, revents, pwake = 0;
	unsigned long flags;
1298
	long user_watches;
L
Linus Torvalds 已提交
1299 1300 1301
	struct epitem *epi;
	struct ep_pqueue epq;

1302 1303
	user_watches = atomic_long_read(&ep->user->epoll_watches);
	if (unlikely(user_watches >= max_user_watches))
1304
		return -ENOSPC;
1305
	if (!(epi = kmem_cache_alloc(epi_cache, GFP_KERNEL)))
1306
		return -ENOMEM;
L
Linus Torvalds 已提交
1307 1308 1309 1310 1311 1312

	/* Item initialization follow here ... */
	INIT_LIST_HEAD(&epi->rdllink);
	INIT_LIST_HEAD(&epi->fllink);
	INIT_LIST_HEAD(&epi->pwqlist);
	epi->ep = ep;
1313
	ep_set_ffd(&epi->ffd, tfile, fd);
L
Linus Torvalds 已提交
1314 1315
	epi->event = *event;
	epi->nwait = 0;
1316
	epi->next = EP_UNACTIVE_PTR;
1317 1318 1319 1320 1321
	if (epi->event.events & EPOLLWAKEUP) {
		error = ep_create_wakeup_source(epi);
		if (error)
			goto error_create_wakeup_source;
	} else {
1322
		RCU_INIT_POINTER(epi->ws, NULL);
1323
	}
L
Linus Torvalds 已提交
1324 1325 1326 1327 1328 1329 1330 1331

	/* Initialize the poll table using the queue callback */
	epq.epi = epi;
	init_poll_funcptr(&epq.pt, ep_ptable_queue_proc);

	/*
	 * Attach the item to the poll hooks and get current event bits.
	 * We can safely use the file* here because its usage count has
1332 1333 1334
	 * been increased by the caller of this function. Note that after
	 * this operation completes, the poll callback can start hitting
	 * the new item.
L
Linus Torvalds 已提交
1335
	 */
1336
	revents = ep_item_poll(epi, &epq.pt);
L
Linus Torvalds 已提交
1337 1338 1339 1340 1341 1342

	/*
	 * We have to check if something went wrong during the poll wait queue
	 * install process. Namely an allocation for a wait queue failed due
	 * high memory pressure.
	 */
1343
	error = -ENOMEM;
L
Linus Torvalds 已提交
1344
	if (epi->nwait < 0)
1345
		goto error_unregister;
L
Linus Torvalds 已提交
1346 1347

	/* Add the current item to the list of active epoll hook for this file */
J
Jonathan Corbet 已提交
1348
	spin_lock(&tfile->f_lock);
1349
	list_add_tail_rcu(&epi->fllink, &tfile->f_ep_links);
J
Jonathan Corbet 已提交
1350
	spin_unlock(&tfile->f_lock);
L
Linus Torvalds 已提交
1351

1352 1353 1354 1355
	/*
	 * Add the current item to the RB tree. All RB tree operations are
	 * protected by "mtx", and ep_insert() is called with "mtx" held.
	 */
L
Linus Torvalds 已提交
1356 1357
	ep_rbtree_insert(ep, epi);

J
Jason Baron 已提交
1358 1359
	/* now check if we've created too many backpaths */
	error = -EINVAL;
1360
	if (full_check && reverse_path_check())
J
Jason Baron 已提交
1361 1362
		goto error_remove_epi;

1363 1364 1365
	/* We have to drop the new item inside our item list to keep track of it */
	spin_lock_irqsave(&ep->lock, flags);

L
Linus Torvalds 已提交
1366
	/* If the file is already "ready" we drop it inside the ready list */
1367
	if ((revents & event->events) && !ep_is_linked(&epi->rdllink)) {
L
Linus Torvalds 已提交
1368
		list_add_tail(&epi->rdllink, &ep->rdllist);
1369
		ep_pm_stay_awake(epi);
L
Linus Torvalds 已提交
1370 1371 1372

		/* Notify waiting tasks that events are available */
		if (waitqueue_active(&ep->wq))
M
Matthew Wilcox 已提交
1373
			wake_up_locked(&ep->wq);
L
Linus Torvalds 已提交
1374 1375 1376 1377
		if (waitqueue_active(&ep->poll_wait))
			pwake++;
	}

1378
	spin_unlock_irqrestore(&ep->lock, flags);
L
Linus Torvalds 已提交
1379

1380
	atomic_long_inc(&ep->user->epoll_watches);
1381

L
Linus Torvalds 已提交
1382 1383
	/* We have to call this outside the lock */
	if (pwake)
D
Davide Libenzi 已提交
1384
		ep_poll_safewake(&ep->poll_wait);
L
Linus Torvalds 已提交
1385 1386 1387

	return 0;

J
Jason Baron 已提交
1388 1389
error_remove_epi:
	spin_lock(&tfile->f_lock);
1390
	list_del_rcu(&epi->fllink);
J
Jason Baron 已提交
1391 1392 1393 1394
	spin_unlock(&tfile->f_lock);

	rb_erase(&epi->rbn, &ep->rbr);

1395
error_unregister:
L
Linus Torvalds 已提交
1396 1397 1398 1399
	ep_unregister_pollwait(ep, epi);

	/*
	 * We need to do this because an event could have been arrived on some
D
Davide Libenzi 已提交
1400 1401 1402
	 * allocated wait queue. Note that we don't care about the ep->ovflist
	 * list, since that is used/cleaned only inside a section bound by "mtx".
	 * And ep_insert() is called with "mtx" held.
L
Linus Torvalds 已提交
1403
	 */
1404
	spin_lock_irqsave(&ep->lock, flags);
1405
	if (ep_is_linked(&epi->rdllink))
1406
		list_del_init(&epi->rdllink);
1407
	spin_unlock_irqrestore(&ep->lock, flags);
L
Linus Torvalds 已提交
1408

1409
	wakeup_source_unregister(ep_wakeup_source(epi));
1410 1411

error_create_wakeup_source:
1412
	kmem_cache_free(epi_cache, epi);
1413

L
Linus Torvalds 已提交
1414 1415 1416 1417 1418
	return error;
}

/*
 * Modify the interest event mask by dropping an event if the new mask
1419
 * has a match in the current file status. Must be called with "mtx" held.
L
Linus Torvalds 已提交
1420 1421 1422 1423 1424
 */
static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_event *event)
{
	int pwake = 0;
	unsigned int revents;
1425 1426 1427
	poll_table pt;

	init_poll_funcptr(&pt, NULL);
L
Linus Torvalds 已提交
1428 1429

	/*
T
Tony Battersby 已提交
1430 1431 1432
	 * Set the new event interest mask before calling f_op->poll();
	 * otherwise we might miss an event that happens between the
	 * f_op->poll() call and the new event set registering.
L
Linus Torvalds 已提交
1433
	 */
1434
	epi->event.events = event->events; /* need barrier below */
T
Tony Battersby 已提交
1435
	epi->event.data = event->data; /* protected by mtx */
1436
	if (epi->event.events & EPOLLWAKEUP) {
1437
		if (!ep_has_wakeup_source(epi))
1438
			ep_create_wakeup_source(epi);
1439
	} else if (ep_has_wakeup_source(epi)) {
1440 1441
		ep_destroy_wakeup_source(epi);
	}
L
Linus Torvalds 已提交
1442

1443 1444 1445 1446 1447 1448 1449 1450 1451 1452 1453 1454 1455 1456 1457 1458 1459 1460 1461 1462
	/*
	 * The following barrier has two effects:
	 *
	 * 1) Flush epi changes above to other CPUs.  This ensures
	 *    we do not miss events from ep_poll_callback if an
	 *    event occurs immediately after we call f_op->poll().
	 *    We need this because we did not take ep->lock while
	 *    changing epi above (but ep_poll_callback does take
	 *    ep->lock).
	 *
	 * 2) We also need to ensure we do not miss _past_ events
	 *    when calling f_op->poll().  This barrier also
	 *    pairs with the barrier in wq_has_sleeper (see
	 *    comments for wq_has_sleeper).
	 *
	 * This barrier will now guarantee ep_poll_callback or f_op->poll
	 * (or both) will notice the readiness of an item.
	 */
	smp_mb();

L
Linus Torvalds 已提交
1463 1464 1465 1466
	/*
	 * Get current event bits. We can safely use the file* here because
	 * its usage count has been increased by the caller of this function.
	 */
1467
	revents = ep_item_poll(epi, &pt);
L
Linus Torvalds 已提交
1468 1469

	/*
1470
	 * If the item is "hot" and it is not registered inside the ready
D
Davide Libenzi 已提交
1471
	 * list, push it inside.
L
Linus Torvalds 已提交
1472
	 */
1473
	if (revents & event->events) {
T
Tony Battersby 已提交
1474
		spin_lock_irq(&ep->lock);
1475 1476
		if (!ep_is_linked(&epi->rdllink)) {
			list_add_tail(&epi->rdllink, &ep->rdllist);
1477
			ep_pm_stay_awake(epi);
1478 1479 1480

			/* Notify waiting tasks that events are available */
			if (waitqueue_active(&ep->wq))
M
Matthew Wilcox 已提交
1481
				wake_up_locked(&ep->wq);
1482 1483
			if (waitqueue_active(&ep->poll_wait))
				pwake++;
1484
		}
T
Tony Battersby 已提交
1485
		spin_unlock_irq(&ep->lock);
1486
	}
L
Linus Torvalds 已提交
1487

1488 1489
	/* We have to call this outside the lock */
	if (pwake)
D
Davide Libenzi 已提交
1490
		ep_poll_safewake(&ep->poll_wait);
L
Linus Torvalds 已提交
1491

1492
	return 0;
L
Linus Torvalds 已提交
1493 1494
}

1495 1496
static int ep_send_events_proc(struct eventpoll *ep, struct list_head *head,
			       void *priv)
L
Linus Torvalds 已提交
1497
{
D
Davide Libenzi 已提交
1498 1499
	struct ep_send_events_data *esed = priv;
	int eventcnt;
1500
	unsigned int revents;
D
Davide Libenzi 已提交
1501 1502
	struct epitem *epi;
	struct epoll_event __user *uevent;
1503
	struct wakeup_source *ws;
1504 1505 1506
	poll_table pt;

	init_poll_funcptr(&pt, NULL);
L
Linus Torvalds 已提交
1507

1508
	/*
D
Davide Libenzi 已提交
1509 1510 1511
	 * We can loop without lock because we are passed a task private list.
	 * Items cannot vanish during the loop because ep_scan_ready_list() is
	 * holding "mtx" during this call.
1512
	 */
D
Davide Libenzi 已提交
1513 1514 1515
	for (eventcnt = 0, uevent = esed->events;
	     !list_empty(head) && eventcnt < esed->maxevents;) {
		epi = list_first_entry(head, struct epitem, rdllink);
1516

1517 1518 1519 1520 1521 1522 1523 1524 1525
		/*
		 * Activate ep->ws before deactivating epi->ws to prevent
		 * triggering auto-suspend here (in case we reactive epi->ws
		 * below).
		 *
		 * This could be rearranged to delay the deactivation of epi->ws
		 * instead, but then epi->ws would temporarily be out of sync
		 * with ep_is_linked().
		 */
1526 1527 1528 1529 1530 1531 1532
		ws = ep_wakeup_source(epi);
		if (ws) {
			if (ws->active)
				__pm_stay_awake(ep->ws);
			__pm_relax(ws);
		}

1533
		list_del_init(&epi->rdllink);
L
Linus Torvalds 已提交
1534

1535
		revents = ep_item_poll(epi, &pt);
D
Davide Libenzi 已提交
1536

1537
		/*
D
Davide Libenzi 已提交
1538 1539 1540 1541
		 * If the event mask intersect the caller-requested one,
		 * deliver the event to userspace. Again, ep_scan_ready_list()
		 * is holding "mtx", so no operations coming from userspace
		 * can change the item.
1542 1543
		 */
		if (revents) {
D
Davide Libenzi 已提交
1544
			if (__put_user(revents, &uevent->events) ||
1545 1546
			    __put_user(epi->event.data, &uevent->data)) {
				list_add(&epi->rdllink, head);
1547
				ep_pm_stay_awake(epi);
1548
				return eventcnt ? eventcnt : -EFAULT;
1549
			}
1550
			eventcnt++;
D
Davide Libenzi 已提交
1551
			uevent++;
1552 1553 1554 1555 1556 1557 1558 1559
			if (epi->event.events & EPOLLONESHOT)
				epi->event.events &= EP_PRIVATE_BITS;
			else if (!(epi->event.events & EPOLLET)) {
				/*
				 * If this file has been added with Level
				 * Trigger mode, we need to insert back inside
				 * the ready list, so that the next call to
				 * epoll_wait() will check again the events
L
Lucas De Marchi 已提交
1560
				 * availability. At this point, no one can insert
1561 1562 1563 1564 1565 1566
				 * into ep->rdllist besides us. The epoll_ctl()
				 * callers are locked out by
				 * ep_scan_ready_list() holding "mtx" and the
				 * poll callback will queue them in ep->ovflist.
				 */
				list_add_tail(&epi->rdllink, &ep->rdllist);
1567
				ep_pm_stay_awake(epi);
1568 1569 1570
			}
		}
	}
D
Davide Libenzi 已提交
1571 1572 1573

	return eventcnt;
}
1574

1575 1576
static int ep_send_events(struct eventpoll *ep,
			  struct epoll_event __user *events, int maxevents)
D
Davide Libenzi 已提交
1577 1578
{
	struct ep_send_events_data esed;
L
Linus Torvalds 已提交
1579

D
Davide Libenzi 已提交
1580 1581
	esed.maxevents = maxevents;
	esed.events = events;
1582

1583
	return ep_scan_ready_list(ep, ep_send_events_proc, &esed, 0, false);
L
Linus Torvalds 已提交
1584 1585
}

1586
static inline struct timespec64 ep_set_mstimeout(long ms)
1587
{
1588
	struct timespec64 now, ts = {
1589 1590 1591 1592
		.tv_sec = ms / MSEC_PER_SEC,
		.tv_nsec = NSEC_PER_MSEC * (ms % MSEC_PER_SEC),
	};

1593 1594
	ktime_get_ts64(&now);
	return timespec64_add_safe(now, ts);
1595 1596
}

1597 1598 1599 1600 1601 1602 1603 1604 1605 1606 1607 1608 1609 1610 1611 1612 1613
/**
 * ep_poll - Retrieves ready events, and delivers them to the caller supplied
 *           event buffer.
 *
 * @ep: Pointer to the eventpoll context.
 * @events: Pointer to the userspace buffer where the ready events should be
 *          stored.
 * @maxevents: Size (in terms of number of events) of the caller event buffer.
 * @timeout: Maximum timeout for the ready events fetch operation, in
 *           milliseconds. If the @timeout is zero, the function will not block,
 *           while if the @timeout is less than zero, the function will block
 *           until at least one event has been retrieved (or an error
 *           occurred).
 *
 * Returns: Returns the number of ready events which have been fetched, or an
 *          error code, in case of error.
 */
L
Linus Torvalds 已提交
1614 1615 1616
static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
		   int maxevents, long timeout)
{
1617
	int res = 0, eavail, timed_out = 0;
L
Linus Torvalds 已提交
1618
	unsigned long flags;
1619
	u64 slack = 0;
L
Linus Torvalds 已提交
1620
	wait_queue_t wait;
1621 1622 1623
	ktime_t expires, *to = NULL;

	if (timeout > 0) {
1624
		struct timespec64 end_time = ep_set_mstimeout(timeout);
1625

1626 1627
		slack = select_estimate_accuracy(&end_time);
		to = &expires;
1628
		*to = timespec64_to_ktime(end_time);
1629
	} else if (timeout == 0) {
1630 1631 1632 1633
		/*
		 * Avoid the unnecessary trip to the wait queue loop, if the
		 * caller specified a non blocking operation.
		 */
1634
		timed_out = 1;
1635 1636
		spin_lock_irqsave(&ep->lock, flags);
		goto check_events;
1637
	}
L
Linus Torvalds 已提交
1638

1639
fetch_events:
1640
	spin_lock_irqsave(&ep->lock, flags);
L
Linus Torvalds 已提交
1641

1642
	if (!ep_events_available(ep)) {
L
Linus Torvalds 已提交
1643 1644 1645 1646 1647 1648
		/*
		 * We don't have any available event to return to the caller.
		 * We need to sleep here, and we will be wake up by
		 * ep_poll_callback() when events will become available.
		 */
		init_waitqueue_entry(&wait, current);
C
Changli Gao 已提交
1649
		__add_wait_queue_exclusive(&ep->wq, &wait);
L
Linus Torvalds 已提交
1650 1651 1652 1653 1654 1655 1656 1657

		for (;;) {
			/*
			 * We don't want to sleep if the ep_poll_callback() sends us
			 * a wakeup in between. That's why we set the task state
			 * to TASK_INTERRUPTIBLE before doing the checks.
			 */
			set_current_state(TASK_INTERRUPTIBLE);
1658
			if (ep_events_available(ep) || timed_out)
L
Linus Torvalds 已提交
1659 1660 1661 1662 1663 1664
				break;
			if (signal_pending(current)) {
				res = -EINTR;
				break;
			}

1665
			spin_unlock_irqrestore(&ep->lock, flags);
1666
			if (!schedule_hrtimeout_range(to, slack, HRTIMER_MODE_ABS))
1667 1668
				timed_out = 1;

1669
			spin_lock_irqsave(&ep->lock, flags);
L
Linus Torvalds 已提交
1670 1671
		}

1672 1673
		__remove_wait_queue(&ep->wq, &wait);
		__set_current_state(TASK_RUNNING);
L
Linus Torvalds 已提交
1674
	}
1675
check_events:
L
Linus Torvalds 已提交
1676
	/* Is it worth to try to dig for events ? */
1677
	eavail = ep_events_available(ep);
L
Linus Torvalds 已提交
1678

1679
	spin_unlock_irqrestore(&ep->lock, flags);
L
Linus Torvalds 已提交
1680 1681 1682 1683 1684 1685 1686

	/*
	 * Try to transfer events to user space. In case we get 0 events and
	 * there's still timeout left over, we go trying again in search of
	 * more luck.
	 */
	if (!res && eavail &&
1687
	    !(res = ep_send_events(ep, events, maxevents)) && !timed_out)
1688
		goto fetch_events;
L
Linus Torvalds 已提交
1689 1690 1691 1692

	return res;
}

1693 1694 1695 1696 1697 1698 1699 1700 1701 1702 1703 1704 1705 1706 1707 1708 1709 1710 1711 1712
/**
 * ep_loop_check_proc - Callback function to be passed to the @ep_call_nested()
 *                      API, to verify that adding an epoll file inside another
 *                      epoll structure, does not violate the constraints, in
 *                      terms of closed loops, or too deep chains (which can
 *                      result in excessive stack usage).
 *
 * @priv: Pointer to the epoll file to be currently checked.
 * @cookie: Original cookie for this call. This is the top-of-the-chain epoll
 *          data structure pointer.
 * @call_nests: Current dept of the @ep_call_nested() call stack.
 *
 * Returns: Returns zero if adding the epoll @file inside current epoll
 *          structure @ep does not violate the constraints, or -1 otherwise.
 */
static int ep_loop_check_proc(void *priv, void *cookie, int call_nests)
{
	int error = 0;
	struct file *file = priv;
	struct eventpoll *ep = file->private_data;
J
Jason Baron 已提交
1713
	struct eventpoll *ep_tovisit;
1714 1715 1716
	struct rb_node *rbp;
	struct epitem *epi;

1717
	mutex_lock_nested(&ep->mtx, call_nests + 1);
J
Jason Baron 已提交
1718 1719
	ep->visited = 1;
	list_add(&ep->visited_list_link, &visited_list);
1720 1721 1722
	for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) {
		epi = rb_entry(rbp, struct epitem, rbn);
		if (unlikely(is_file_epoll(epi->ffd.file))) {
J
Jason Baron 已提交
1723 1724 1725
			ep_tovisit = epi->ffd.file->private_data;
			if (ep_tovisit->visited)
				continue;
1726
			error = ep_call_nested(&poll_loop_ncalls, EP_MAX_NESTS,
J
Jason Baron 已提交
1727 1728
					ep_loop_check_proc, epi->ffd.file,
					ep_tovisit, current);
1729 1730
			if (error != 0)
				break;
J
Jason Baron 已提交
1731 1732 1733 1734 1735 1736 1737 1738 1739 1740 1741 1742
		} else {
			/*
			 * If we've reached a file that is not associated with
			 * an ep, then we need to check if the newly added
			 * links are going to add too many wakeup paths. We do
			 * this by adding it to the tfile_check_list, if it's
			 * not already there, and calling reverse_path_check()
			 * during ep_insert().
			 */
			if (list_empty(&epi->ffd.file->f_tfile_llink))
				list_add(&epi->ffd.file->f_tfile_llink,
					 &tfile_check_list);
1743 1744 1745 1746 1747 1748 1749 1750 1751 1752 1753 1754 1755 1756 1757 1758 1759 1760 1761 1762
		}
	}
	mutex_unlock(&ep->mtx);

	return error;
}

/**
 * ep_loop_check - Performs a check to verify that adding an epoll file (@file)
 *                 another epoll file (represented by @ep) does not create
 *                 closed loops or too deep chains.
 *
 * @ep: Pointer to the epoll private data structure.
 * @file: Pointer to the epoll file to be checked.
 *
 * Returns: Returns zero if adding the epoll @file inside current epoll
 *          structure @ep does not violate the constraints, or -1 otherwise.
 */
static int ep_loop_check(struct eventpoll *ep, struct file *file)
{
J
Jason Baron 已提交
1763 1764 1765 1766
	int ret;
	struct eventpoll *ep_cur, *ep_next;

	ret = ep_call_nested(&poll_loop_ncalls, EP_MAX_NESTS,
1767
			      ep_loop_check_proc, file, ep, current);
J
Jason Baron 已提交
1768 1769 1770 1771 1772 1773 1774 1775 1776 1777 1778 1779 1780 1781 1782 1783 1784 1785 1786 1787
	/* clear visited list */
	list_for_each_entry_safe(ep_cur, ep_next, &visited_list,
							visited_list_link) {
		ep_cur->visited = 0;
		list_del(&ep_cur->visited_list_link);
	}
	return ret;
}

static void clear_tfile_check_list(void)
{
	struct file *file;

	/* first clear the tfile_check_list */
	while (!list_empty(&tfile_check_list)) {
		file = list_first_entry(&tfile_check_list, struct file,
					f_tfile_llink);
		list_del_init(&file->f_tfile_llink);
	}
	INIT_LIST_HEAD(&tfile_check_list);
1788 1789
}

1790
/*
1791
 * Open an eventpoll file descriptor.
1792
 */
1793
SYSCALL_DEFINE1(epoll_create1, int, flags)
1794
{
J
Jason Baron 已提交
1795
	int error, fd;
D
Davide Libenzi 已提交
1796
	struct eventpoll *ep = NULL;
J
Jason Baron 已提交
1797
	struct file *file;
1798

1799 1800 1801
	/* Check the EPOLL_* constant for consistency.  */
	BUILD_BUG_ON(EPOLL_CLOEXEC != O_CLOEXEC);

1802 1803
	if (flags & ~EPOLL_CLOEXEC)
		return -EINVAL;
1804
	/*
D
Davide Libenzi 已提交
1805
	 * Create the internal data structure ("struct eventpoll").
1806
	 */
1807
	error = ep_alloc(&ep);
D
Davide Libenzi 已提交
1808 1809
	if (error < 0)
		return error;
1810 1811
	/*
	 * Creates all the items needed to setup an eventpoll file. That is,
A
Al Viro 已提交
1812
	 * a file structure and a free file descriptor.
1813
	 */
J
Jason Baron 已提交
1814 1815 1816 1817 1818 1819
	fd = get_unused_fd_flags(O_RDWR | (flags & O_CLOEXEC));
	if (fd < 0) {
		error = fd;
		goto out_free_ep;
	}
	file = anon_inode_getfile("[eventpoll]", &eventpoll_fops, ep,
1820
				 O_RDWR | (flags & O_CLOEXEC));
J
Jason Baron 已提交
1821 1822 1823 1824 1825
	if (IS_ERR(file)) {
		error = PTR_ERR(file);
		goto out_free_fd;
	}
	ep->file = file;
1826
	fd_install(fd, file);
J
Jason Baron 已提交
1827 1828 1829 1830 1831 1832
	return fd;

out_free_fd:
	put_unused_fd(fd);
out_free_ep:
	ep_free(ep);
D
Davide Libenzi 已提交
1833
	return error;
1834 1835
}

1836
SYSCALL_DEFINE1(epoll_create, int, size)
U
Ulrich Drepper 已提交
1837
{
1838
	if (size <= 0)
1839 1840 1841
		return -EINVAL;

	return sys_epoll_create1(0);
U
Ulrich Drepper 已提交
1842 1843
}

1844 1845 1846
/*
 * The following function implements the controller interface for
 * the eventpoll file that enables the insertion/removal/change of
D
Davide Libenzi 已提交
1847
 * file descriptors inside the interest set.
1848
 */
1849 1850
SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
		struct epoll_event __user *, event)
1851 1852
{
	int error;
1853
	int full_check = 0;
A
Al Viro 已提交
1854
	struct fd f, tf;
1855 1856 1857
	struct eventpoll *ep;
	struct epitem *epi;
	struct epoll_event epds;
1858
	struct eventpoll *tep = NULL;
1859 1860 1861 1862 1863 1864 1865

	error = -EFAULT;
	if (ep_op_has_event(op) &&
	    copy_from_user(&epds, event, sizeof(struct epoll_event)))
		goto error_return;

	error = -EBADF;
A
Al Viro 已提交
1866 1867
	f = fdget(epfd);
	if (!f.file)
1868 1869 1870
		goto error_return;

	/* Get the "struct file *" for the target file */
A
Al Viro 已提交
1871 1872
	tf = fdget(fd);
	if (!tf.file)
1873 1874 1875 1876
		goto error_fput;

	/* The target file descriptor must support poll */
	error = -EPERM;
A
Al Viro 已提交
1877
	if (!tf.file->f_op->poll)
1878 1879
		goto error_tgt_fput;

1880
	/* Check if EPOLLWAKEUP is allowed */
1881 1882
	if (ep_op_has_event(op))
		ep_take_care_of_epollwakeup(&epds);
1883

1884 1885 1886 1887 1888 1889
	/*
	 * We have to check that the file structure underneath the file descriptor
	 * the user passed to us _is_ an eventpoll file. And also we do not permit
	 * adding an epoll file descriptor inside itself.
	 */
	error = -EINVAL;
A
Al Viro 已提交
1890
	if (f.file == tf.file || !is_file_epoll(f.file))
1891 1892
		goto error_tgt_fput;

J
Jason Baron 已提交
1893 1894 1895 1896 1897
	/*
	 * epoll adds to the wakeup queue at EPOLL_CTL_ADD time only,
	 * so EPOLLEXCLUSIVE is not allowed for a EPOLL_CTL_MOD operation.
	 * Also, we do not currently supported nested exclusive wakeups.
	 */
1898
	if (ep_op_has_event(op) && (epds.events & EPOLLEXCLUSIVE)) {
1899 1900 1901 1902 1903 1904
		if (op == EPOLL_CTL_MOD)
			goto error_tgt_fput;
		if (op == EPOLL_CTL_ADD && (is_file_epoll(tf.file) ||
				(epds.events & ~EPOLLEXCLUSIVE_OK_BITS)))
			goto error_tgt_fput;
	}
J
Jason Baron 已提交
1905

1906 1907 1908 1909
	/*
	 * At this point it is safe to assume that the "private_data" contains
	 * our own data structure.
	 */
A
Al Viro 已提交
1910
	ep = f.file->private_data;
1911

1912 1913 1914
	/*
	 * When we insert an epoll file descriptor, inside another epoll file
	 * descriptor, there is the change of creating closed loops, which are
J
Jason Baron 已提交
1915 1916 1917 1918
	 * better be handled here, than in more critical paths. While we are
	 * checking for loops we also determine the list of files reachable
	 * and hang them on the tfile_check_list, so we can check that we
	 * haven't created too many possible wakeup paths.
1919
	 *
1920 1921 1922 1923 1924 1925
	 * We do not need to take the global 'epumutex' on EPOLL_CTL_ADD when
	 * the epoll file descriptor is attaching directly to a wakeup source,
	 * unless the epoll file descriptor is nested. The purpose of taking the
	 * 'epmutex' on add is to prevent complex toplogies such as loops and
	 * deep wakeup paths from forming in parallel through multiple
	 * EPOLL_CTL_ADD operations.
1926
	 */
1927
	mutex_lock_nested(&ep->mtx, 0);
J
Jason Baron 已提交
1928
	if (op == EPOLL_CTL_ADD) {
1929 1930 1931 1932 1933 1934 1935 1936 1937 1938 1939 1940 1941 1942 1943 1944 1945 1946
		if (!list_empty(&f.file->f_ep_links) ||
						is_file_epoll(tf.file)) {
			full_check = 1;
			mutex_unlock(&ep->mtx);
			mutex_lock(&epmutex);
			if (is_file_epoll(tf.file)) {
				error = -ELOOP;
				if (ep_loop_check(ep, tf.file) != 0) {
					clear_tfile_check_list();
					goto error_tgt_fput;
				}
			} else
				list_add(&tf.file->f_tfile_llink,
							&tfile_check_list);
			mutex_lock_nested(&ep->mtx, 0);
			if (is_file_epoll(tf.file)) {
				tep = tf.file->private_data;
				mutex_lock_nested(&tep->mtx, 1);
1947
			}
1948 1949
		}
	}
1950

D
Davide Libenzi 已提交
1951 1952 1953 1954 1955
	/*
	 * Try to lookup the file inside our RB tree, Since we grabbed "mtx"
	 * above, we can be sure to be able to use the item looked up by
	 * ep_find() till we release the mutex.
	 */
A
Al Viro 已提交
1956
	epi = ep_find(ep, tf.file, fd);
1957 1958 1959 1960 1961 1962

	error = -EINVAL;
	switch (op) {
	case EPOLL_CTL_ADD:
		if (!epi) {
			epds.events |= POLLERR | POLLHUP;
1963
			error = ep_insert(ep, &epds, tf.file, fd, full_check);
1964 1965
		} else
			error = -EEXIST;
1966 1967
		if (full_check)
			clear_tfile_check_list();
1968 1969 1970 1971 1972 1973 1974 1975 1976
		break;
	case EPOLL_CTL_DEL:
		if (epi)
			error = ep_remove(ep, epi);
		else
			error = -ENOENT;
		break;
	case EPOLL_CTL_MOD:
		if (epi) {
1977 1978 1979 1980
			if (!(epi->event.events & EPOLLEXCLUSIVE)) {
				epds.events |= POLLERR | POLLHUP;
				error = ep_modify(ep, epi, &epds);
			}
1981 1982 1983 1984
		} else
			error = -ENOENT;
		break;
	}
1985 1986
	if (tep != NULL)
		mutex_unlock(&tep->mtx);
1987
	mutex_unlock(&ep->mtx);
1988 1989

error_tgt_fput:
1990
	if (full_check)
1991 1992
		mutex_unlock(&epmutex);

A
Al Viro 已提交
1993
	fdput(tf);
1994
error_fput:
A
Al Viro 已提交
1995
	fdput(f);
1996 1997 1998 1999 2000 2001 2002 2003 2004
error_return:

	return error;
}

/*
 * Implement the event wait interface for the eventpoll file. It is the kernel
 * part of the user space epoll_wait(2).
 */
2005 2006
SYSCALL_DEFINE4(epoll_wait, int, epfd, struct epoll_event __user *, events,
		int, maxevents, int, timeout)
2007
{
2008 2009
	int error;
	struct fd f;
2010 2011 2012 2013 2014 2015 2016
	struct eventpoll *ep;

	/* The maximum number of event must be greater than zero */
	if (maxevents <= 0 || maxevents > EP_MAX_EVENTS)
		return -EINVAL;

	/* Verify that the area passed by the user is writeable */
2017 2018
	if (!access_ok(VERIFY_WRITE, events, maxevents * sizeof(struct epoll_event)))
		return -EFAULT;
2019 2020

	/* Get the "struct file *" for the eventpoll file */
2021 2022 2023
	f = fdget(epfd);
	if (!f.file)
		return -EBADF;
2024 2025 2026 2027 2028 2029

	/*
	 * We have to check that the file structure underneath the fd
	 * the user passed to us _is_ an eventpoll file.
	 */
	error = -EINVAL;
2030
	if (!is_file_epoll(f.file))
2031 2032 2033 2034 2035 2036
		goto error_fput;

	/*
	 * At this point it is safe to assume that the "private_data" contains
	 * our own data structure.
	 */
2037
	ep = f.file->private_data;
2038 2039 2040 2041 2042

	/* Time to fish for events ... */
	error = ep_poll(ep, events, maxevents, timeout);

error_fput:
2043
	fdput(f);
2044 2045 2046 2047 2048 2049 2050
	return error;
}

/*
 * Implement the event wait interface for the eventpoll file. It is the kernel
 * part of the user space epoll_pwait(2).
 */
2051 2052 2053
SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, events,
		int, maxevents, int, timeout, const sigset_t __user *, sigmask,
		size_t, sigsetsize)
2054 2055 2056 2057 2058 2059 2060 2061 2062 2063 2064 2065 2066
{
	int error;
	sigset_t ksigmask, sigsaved;

	/*
	 * If the caller wants a certain signal mask to be set during the wait,
	 * we apply it here.
	 */
	if (sigmask) {
		if (sigsetsize != sizeof(sigset_t))
			return -EINVAL;
		if (copy_from_user(&ksigmask, sigmask, sizeof(ksigmask)))
			return -EFAULT;
2067 2068
		sigsaved = current->blocked;
		set_current_blocked(&ksigmask);
2069 2070 2071 2072 2073 2074 2075 2076 2077 2078 2079 2080 2081
	}

	error = sys_epoll_wait(epfd, events, maxevents, timeout);

	/*
	 * If we changed the signal mask, we need to restore the original one.
	 * In case we've got a signal while waiting, we do not restore the
	 * signal mask yet, and we allow do_signal() to deliver the signal on
	 * the way back to userspace, before the signal mask is restored.
	 */
	if (sigmask) {
		if (error == -EINTR) {
			memcpy(&current->saved_sigmask, &sigsaved,
2082
			       sizeof(sigsaved));
2083
			set_restore_sigmask();
2084
		} else
2085
			set_current_blocked(&sigsaved);
2086 2087 2088 2089 2090
	}

	return error;
}

2091 2092 2093 2094 2095 2096 2097 2098 2099 2100 2101 2102 2103 2104 2105 2106 2107 2108 2109 2110 2111
#ifdef CONFIG_COMPAT
COMPAT_SYSCALL_DEFINE6(epoll_pwait, int, epfd,
			struct epoll_event __user *, events,
			int, maxevents, int, timeout,
			const compat_sigset_t __user *, sigmask,
			compat_size_t, sigsetsize)
{
	long err;
	compat_sigset_t csigmask;
	sigset_t ksigmask, sigsaved;

	/*
	 * If the caller wants a certain signal mask to be set during the wait,
	 * we apply it here.
	 */
	if (sigmask) {
		if (sigsetsize != sizeof(compat_sigset_t))
			return -EINVAL;
		if (copy_from_user(&csigmask, sigmask, sizeof(csigmask)))
			return -EFAULT;
		sigset_from_compat(&ksigmask, &csigmask);
2112 2113
		sigsaved = current->blocked;
		set_current_blocked(&ksigmask);
2114 2115 2116 2117 2118 2119 2120 2121 2122 2123 2124 2125 2126 2127 2128 2129
	}

	err = sys_epoll_wait(epfd, events, maxevents, timeout);

	/*
	 * If we changed the signal mask, we need to restore the original one.
	 * In case we've got a signal while waiting, we do not restore the
	 * signal mask yet, and we allow do_signal() to deliver the signal on
	 * the way back to userspace, before the signal mask is restored.
	 */
	if (sigmask) {
		if (err == -EINTR) {
			memcpy(&current->saved_sigmask, &sigsaved,
			       sizeof(sigsaved));
			set_restore_sigmask();
		} else
2130
			set_current_blocked(&sigsaved);
2131 2132 2133 2134 2135 2136
	}

	return err;
}
#endif

L
Linus Torvalds 已提交
2137 2138
static int __init eventpoll_init(void)
{
2139 2140 2141
	struct sysinfo si;

	si_meminfo(&si);
2142 2143 2144 2145
	/*
	 * Allows top 4% of lomem to be allocated for epoll watches (per user).
	 */
	max_user_watches = (((si.totalram - si.totalhigh) / 25) << PAGE_SHIFT) /
2146
		EP_ITEM_COST;
2147
	BUG_ON(max_user_watches < 0);
L
Linus Torvalds 已提交
2148

2149 2150 2151 2152 2153 2154
	/*
	 * Initialize the structure used to perform epoll file descriptor
	 * inclusion loops checks.
	 */
	ep_nested_calls_init(&poll_loop_ncalls);

L
Linus Torvalds 已提交
2155
	/* Initialize the structure used to perform safe poll wait head wake ups */
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	ep_nested_calls_init(&poll_safewake_ncalls);

	/* Initialize the structure used to perform file's f_op->poll() calls */
	ep_nested_calls_init(&poll_readywalk_ncalls);
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	/*
	 * We can have many thousands of epitems, so prevent this from
	 * using an extra cache line on 64-bit (and smaller) CPUs
	 */
	BUILD_BUG_ON(sizeof(void *) <= 8 && sizeof(struct epitem) > 128);

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	/* Allocates slab cache used to allocate "struct epitem" items */
	epi_cache = kmem_cache_create("eventpoll_epi", sizeof(struct epitem),
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			0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
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	/* Allocates slab cache used to allocate "struct eppoll_entry" */
	pwq_cache = kmem_cache_create("eventpoll_pwq",
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			sizeof(struct eppoll_entry), 0, SLAB_PANIC, NULL);
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	return 0;
}
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fs_initcall(eventpoll_init);