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/*
 * Read-Copy Update mechanism for mutual exclusion
 *
 * 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.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
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 * along with this program; if not, you can access it online at
 * http://www.gnu.org/licenses/gpl-2.0.html.
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 *
 * Copyright IBM Corporation, 2008
 *
 * Authors: Dipankar Sarma <dipankar@in.ibm.com>
 *	    Manfred Spraul <manfred@colorfullife.com>
 *	    Paul E. McKenney <paulmck@linux.vnet.ibm.com> Hierarchical version
 *
 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
 *
 * For detailed explanation of Read-Copy Update mechanism see -
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 *	Documentation/RCU
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 */
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/spinlock.h>
#include <linux/smp.h>
#include <linux/rcupdate.h>
#include <linux/interrupt.h>
#include <linux/sched.h>
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#include <linux/nmi.h>
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#include <linux/atomic.h>
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#include <linux/bitops.h>
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#include <linux/export.h>
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#include <linux/completion.h>
#include <linux/moduleparam.h>
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#include <linux/module.h>
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#include <linux/percpu.h>
#include <linux/notifier.h>
#include <linux/cpu.h>
#include <linux/mutex.h>
#include <linux/time.h>
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#include <linux/kernel_stat.h>
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#include <linux/wait.h>
#include <linux/kthread.h>
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#include <linux/prefetch.h>
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#include <linux/delay.h>
#include <linux/stop_machine.h>
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#include <linux/random.h>
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#include <linux/ftrace_event.h>
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#include <linux/suspend.h>
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#include "tree.h"
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#include "rcu.h"
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MODULE_ALIAS("rcutree");
#ifdef MODULE_PARAM_PREFIX
#undef MODULE_PARAM_PREFIX
#endif
#define MODULE_PARAM_PREFIX "rcutree."

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/* Data structures. */

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static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
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static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
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/*
 * In order to export the rcu_state name to the tracing tools, it
 * needs to be added in the __tracepoint_string section.
 * This requires defining a separate variable tp_<sname>_varname
 * that points to the string being used, and this will allow
 * the tracing userspace tools to be able to decipher the string
 * address to the matching string.
 */
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#ifdef CONFIG_TRACING
# define DEFINE_RCU_TPS(sname) \
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static char sname##_varname[] = #sname; \
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static const char *tp_##sname##_varname __used __tracepoint_string = sname##_varname;
# define RCU_STATE_NAME(sname) sname##_varname
#else
# define DEFINE_RCU_TPS(sname)
# define RCU_STATE_NAME(sname) __stringify(sname)
#endif

#define RCU_STATE_INITIALIZER(sname, sabbr, cr) \
DEFINE_RCU_TPS(sname) \
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DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, sname##_data); \
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struct rcu_state sname##_state = { \
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	.level = { &sname##_state.node[0] }, \
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	.rda = &sname##_data, \
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	.call = cr, \
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	.fqs_state = RCU_GP_IDLE, \
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	.gpnum = 0UL - 300UL, \
	.completed = 0UL - 300UL, \
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	.orphan_lock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.orphan_lock), \
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	.orphan_nxttail = &sname##_state.orphan_nxtlist, \
	.orphan_donetail = &sname##_state.orphan_donelist, \
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	.barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \
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	.name = RCU_STATE_NAME(sname), \
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	.abbr = sabbr, \
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}
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RCU_STATE_INITIALIZER(rcu_sched, 's', call_rcu_sched);
RCU_STATE_INITIALIZER(rcu_bh, 'b', call_rcu_bh);
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static struct rcu_state *rcu_state_p;
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LIST_HEAD(rcu_struct_flavors);
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/* Increase (but not decrease) the CONFIG_RCU_FANOUT_LEAF at boot time. */
static int rcu_fanout_leaf = CONFIG_RCU_FANOUT_LEAF;
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module_param(rcu_fanout_leaf, int, 0444);
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int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;
static int num_rcu_lvl[] = {  /* Number of rcu_nodes at specified level. */
	NUM_RCU_LVL_0,
	NUM_RCU_LVL_1,
	NUM_RCU_LVL_2,
	NUM_RCU_LVL_3,
	NUM_RCU_LVL_4,
};
int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */

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/*
 * The rcu_scheduler_active variable transitions from zero to one just
 * before the first task is spawned.  So when this variable is zero, RCU
 * can assume that there is but one task, allowing RCU to (for example)
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 * optimize synchronize_sched() to a simple barrier().  When this variable
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 * is one, RCU must actually do all the hard work required to detect real
 * grace periods.  This variable is also used to suppress boot-time false
 * positives from lockdep-RCU error checking.
 */
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int rcu_scheduler_active __read_mostly;
EXPORT_SYMBOL_GPL(rcu_scheduler_active);

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/*
 * The rcu_scheduler_fully_active variable transitions from zero to one
 * during the early_initcall() processing, which is after the scheduler
 * is capable of creating new tasks.  So RCU processing (for example,
 * creating tasks for RCU priority boosting) must be delayed until after
 * rcu_scheduler_fully_active transitions from zero to one.  We also
 * currently delay invocation of any RCU callbacks until after this point.
 *
 * It might later prove better for people registering RCU callbacks during
 * early boot to take responsibility for these callbacks, but one step at
 * a time.
 */
static int rcu_scheduler_fully_active __read_mostly;

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static void rcu_init_new_rnp(struct rcu_node *rnp_leaf);
static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf);
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static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu);
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static void invoke_rcu_core(void);
static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp);
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/* rcuc/rcub kthread realtime priority */
static int kthread_prio = CONFIG_RCU_KTHREAD_PRIO;
module_param(kthread_prio, int, 0644);

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/* Delay in jiffies for grace-period initialization delays, debug only. */
#ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT
static int gp_init_delay = CONFIG_RCU_TORTURE_TEST_SLOW_INIT_DELAY;
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module_param(gp_init_delay, int, 0644);
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#else /* #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT */
static const int gp_init_delay;
#endif /* #else #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT */
#define PER_RCU_NODE_PERIOD 10	/* Number of grace periods between delays. */
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/*
 * Track the rcutorture test sequence number and the update version
 * number within a given test.  The rcutorture_testseq is incremented
 * on every rcutorture module load and unload, so has an odd value
 * when a test is running.  The rcutorture_vernum is set to zero
 * when rcutorture starts and is incremented on each rcutorture update.
 * These variables enable correlating rcutorture output with the
 * RCU tracing information.
 */
unsigned long rcutorture_testseq;
unsigned long rcutorture_vernum;

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/*
 * Compute the mask of online CPUs for the specified rcu_node structure.
 * This will not be stable unless the rcu_node structure's ->lock is
 * held, but the bit corresponding to the current CPU will be stable
 * in most contexts.
 */
unsigned long rcu_rnp_online_cpus(struct rcu_node *rnp)
{
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	return READ_ONCE(rnp->qsmaskinitnext);
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}

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/*
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 * Return true if an RCU grace period is in progress.  The READ_ONCE()s
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 * permit this function to be invoked without holding the root rcu_node
 * structure's ->lock, but of course results can be subject to change.
 */
static int rcu_gp_in_progress(struct rcu_state *rsp)
{
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	return READ_ONCE(rsp->completed) != READ_ONCE(rsp->gpnum);
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}

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/*
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 * Note a quiescent state.  Because we do not need to know
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 * how many quiescent states passed, just if there was at least
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 * one since the start of the grace period, this just sets a flag.
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 * The caller must have disabled preemption.
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 */
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void rcu_sched_qs(void)
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{
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	if (!__this_cpu_read(rcu_sched_data.passed_quiesce)) {
		trace_rcu_grace_period(TPS("rcu_sched"),
				       __this_cpu_read(rcu_sched_data.gpnum),
				       TPS("cpuqs"));
		__this_cpu_write(rcu_sched_data.passed_quiesce, 1);
	}
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}

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void rcu_bh_qs(void)
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{
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	if (!__this_cpu_read(rcu_bh_data.passed_quiesce)) {
		trace_rcu_grace_period(TPS("rcu_bh"),
				       __this_cpu_read(rcu_bh_data.gpnum),
				       TPS("cpuqs"));
		__this_cpu_write(rcu_bh_data.passed_quiesce, 1);
	}
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}
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static DEFINE_PER_CPU(int, rcu_sched_qs_mask);

static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
	.dynticks_nesting = DYNTICK_TASK_EXIT_IDLE,
	.dynticks = ATOMIC_INIT(1),
#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
	.dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE,
	.dynticks_idle = ATOMIC_INIT(1),
#endif /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
};

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DEFINE_PER_CPU_SHARED_ALIGNED(unsigned long, rcu_qs_ctr);
EXPORT_PER_CPU_SYMBOL_GPL(rcu_qs_ctr);

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/*
 * Let the RCU core know that this CPU has gone through the scheduler,
 * which is a quiescent state.  This is called when the need for a
 * quiescent state is urgent, so we burn an atomic operation and full
 * memory barriers to let the RCU core know about it, regardless of what
 * this CPU might (or might not) do in the near future.
 *
 * We inform the RCU core by emulating a zero-duration dyntick-idle
 * period, which we in turn do by incrementing the ->dynticks counter
 * by two.
 */
static void rcu_momentary_dyntick_idle(void)
{
	unsigned long flags;
	struct rcu_data *rdp;
	struct rcu_dynticks *rdtp;
	int resched_mask;
	struct rcu_state *rsp;

	local_irq_save(flags);

	/*
	 * Yes, we can lose flag-setting operations.  This is OK, because
	 * the flag will be set again after some delay.
	 */
	resched_mask = raw_cpu_read(rcu_sched_qs_mask);
	raw_cpu_write(rcu_sched_qs_mask, 0);

	/* Find the flavor that needs a quiescent state. */
	for_each_rcu_flavor(rsp) {
		rdp = raw_cpu_ptr(rsp->rda);
		if (!(resched_mask & rsp->flavor_mask))
			continue;
		smp_mb(); /* rcu_sched_qs_mask before cond_resched_completed. */
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		if (READ_ONCE(rdp->mynode->completed) !=
		    READ_ONCE(rdp->cond_resched_completed))
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			continue;

		/*
		 * Pretend to be momentarily idle for the quiescent state.
		 * This allows the grace-period kthread to record the
		 * quiescent state, with no need for this CPU to do anything
		 * further.
		 */
		rdtp = this_cpu_ptr(&rcu_dynticks);
		smp_mb__before_atomic(); /* Earlier stuff before QS. */
		atomic_add(2, &rdtp->dynticks);  /* QS. */
		smp_mb__after_atomic(); /* Later stuff after QS. */
		break;
	}
	local_irq_restore(flags);
}

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/*
 * Note a context switch.  This is a quiescent state for RCU-sched,
 * and requires special handling for preemptible RCU.
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 * The caller must have disabled preemption.
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 */
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void rcu_note_context_switch(void)
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{
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	trace_rcu_utilization(TPS("Start context switch"));
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	rcu_sched_qs();
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	rcu_preempt_note_context_switch();
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	if (unlikely(raw_cpu_read(rcu_sched_qs_mask)))
		rcu_momentary_dyntick_idle();
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	trace_rcu_utilization(TPS("End context switch"));
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}
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EXPORT_SYMBOL_GPL(rcu_note_context_switch);
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/*
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 * Register a quiescent state for all RCU flavors.  If there is an
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 * emergency, invoke rcu_momentary_dyntick_idle() to do a heavy-weight
 * dyntick-idle quiescent state visible to other CPUs (but only for those
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 * RCU flavors in desperate need of a quiescent state, which will normally
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 * be none of them).  Either way, do a lightweight quiescent state for
 * all RCU flavors.
 */
void rcu_all_qs(void)
{
	if (unlikely(raw_cpu_read(rcu_sched_qs_mask)))
		rcu_momentary_dyntick_idle();
	this_cpu_inc(rcu_qs_ctr);
}
EXPORT_SYMBOL_GPL(rcu_all_qs);

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static long blimit = 10;	/* Maximum callbacks per rcu_do_batch. */
static long qhimark = 10000;	/* If this many pending, ignore blimit. */
static long qlowmark = 100;	/* Once only this many pending, use blimit. */
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module_param(blimit, long, 0444);
module_param(qhimark, long, 0444);
module_param(qlowmark, long, 0444);
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static ulong jiffies_till_first_fqs = ULONG_MAX;
static ulong jiffies_till_next_fqs = ULONG_MAX;
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module_param(jiffies_till_first_fqs, ulong, 0644);
module_param(jiffies_till_next_fqs, ulong, 0644);

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/*
 * How long the grace period must be before we start recruiting
 * quiescent-state help from rcu_note_context_switch().
 */
static ulong jiffies_till_sched_qs = HZ / 20;
module_param(jiffies_till_sched_qs, ulong, 0644);

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static bool rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
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				  struct rcu_data *rdp);
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static void force_qs_rnp(struct rcu_state *rsp,
			 int (*f)(struct rcu_data *rsp, bool *isidle,
				  unsigned long *maxj),
			 bool *isidle, unsigned long *maxj);
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static void force_quiescent_state(struct rcu_state *rsp);
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static int rcu_pending(void);
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/*
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 * Return the number of RCU batches started thus far for debug & stats.
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 */
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unsigned long rcu_batches_started(void)
{
	return rcu_state_p->gpnum;
}
EXPORT_SYMBOL_GPL(rcu_batches_started);

/*
 * Return the number of RCU-sched batches started thus far for debug & stats.
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 */
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unsigned long rcu_batches_started_sched(void)
{
	return rcu_sched_state.gpnum;
}
EXPORT_SYMBOL_GPL(rcu_batches_started_sched);

/*
 * Return the number of RCU BH batches started thus far for debug & stats.
 */
unsigned long rcu_batches_started_bh(void)
{
	return rcu_bh_state.gpnum;
}
EXPORT_SYMBOL_GPL(rcu_batches_started_bh);

/*
 * Return the number of RCU batches completed thus far for debug & stats.
 */
unsigned long rcu_batches_completed(void)
{
	return rcu_state_p->completed;
}
EXPORT_SYMBOL_GPL(rcu_batches_completed);

/*
 * Return the number of RCU-sched batches completed thus far for debug & stats.
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 */
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unsigned long rcu_batches_completed_sched(void)
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{
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	return rcu_sched_state.completed;
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}
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EXPORT_SYMBOL_GPL(rcu_batches_completed_sched);
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/*
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 * Return the number of RCU BH batches completed thus far for debug & stats.
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 */
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unsigned long rcu_batches_completed_bh(void)
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{
	return rcu_bh_state.completed;
}
EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);

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/*
 * Force a quiescent state.
 */
void rcu_force_quiescent_state(void)
{
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	force_quiescent_state(rcu_state_p);
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}
EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);

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/*
 * Force a quiescent state for RCU BH.
 */
void rcu_bh_force_quiescent_state(void)
{
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	force_quiescent_state(&rcu_bh_state);
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}
EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state);

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/*
 * Force a quiescent state for RCU-sched.
 */
void rcu_sched_force_quiescent_state(void)
{
	force_quiescent_state(&rcu_sched_state);
}
EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state);

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/*
 * Show the state of the grace-period kthreads.
 */
void show_rcu_gp_kthreads(void)
{
	struct rcu_state *rsp;

	for_each_rcu_flavor(rsp) {
		pr_info("%s: wait state: %d ->state: %#lx\n",
			rsp->name, rsp->gp_state, rsp->gp_kthread->state);
		/* sched_show_task(rsp->gp_kthread); */
	}
}
EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads);

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/*
 * Record the number of times rcutorture tests have been initiated and
 * terminated.  This information allows the debugfs tracing stats to be
 * correlated to the rcutorture messages, even when the rcutorture module
 * is being repeatedly loaded and unloaded.  In other words, we cannot
 * store this state in rcutorture itself.
 */
void rcutorture_record_test_transition(void)
{
	rcutorture_testseq++;
	rcutorture_vernum = 0;
}
EXPORT_SYMBOL_GPL(rcutorture_record_test_transition);

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/*
 * Send along grace-period-related data for rcutorture diagnostics.
 */
void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
			    unsigned long *gpnum, unsigned long *completed)
{
	struct rcu_state *rsp = NULL;

	switch (test_type) {
	case RCU_FLAVOR:
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		rsp = rcu_state_p;
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		break;
	case RCU_BH_FLAVOR:
		rsp = &rcu_bh_state;
		break;
	case RCU_SCHED_FLAVOR:
		rsp = &rcu_sched_state;
		break;
	default:
		break;
	}
	if (rsp != NULL) {
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		*flags = READ_ONCE(rsp->gp_flags);
		*gpnum = READ_ONCE(rsp->gpnum);
		*completed = READ_ONCE(rsp->completed);
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		return;
	}
	*flags = 0;
	*gpnum = 0;
	*completed = 0;
}
EXPORT_SYMBOL_GPL(rcutorture_get_gp_data);

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/*
 * Record the number of writer passes through the current rcutorture test.
 * This is also used to correlate debugfs tracing stats with the rcutorture
 * messages.
 */
void rcutorture_record_progress(unsigned long vernum)
{
	rcutorture_vernum++;
}
EXPORT_SYMBOL_GPL(rcutorture_record_progress);

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/*
 * Does the CPU have callbacks ready to be invoked?
 */
static int
cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp)
{
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	return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL] &&
	       rdp->nxttail[RCU_DONE_TAIL] != NULL;
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}

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/*
 * Return the root node of the specified rcu_state structure.
 */
static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
{
	return &rsp->node[0];
}

/*
 * Is there any need for future grace periods?
 * Interrupts must be disabled.  If the caller does not hold the root
 * rnp_node structure's ->lock, the results are advisory only.
 */
static int rcu_future_needs_gp(struct rcu_state *rsp)
{
	struct rcu_node *rnp = rcu_get_root(rsp);
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	int idx = (READ_ONCE(rnp->completed) + 1) & 0x1;
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	int *fp = &rnp->need_future_gp[idx];

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	return READ_ONCE(*fp);
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}

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/*
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 * Does the current CPU require a not-yet-started grace period?
 * The caller must have disabled interrupts to prevent races with
 * normal callback registry.
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 */
static int
cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
{
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	int i;
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	if (rcu_gp_in_progress(rsp))
		return 0;  /* No, a grace period is already in progress. */
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	if (rcu_future_needs_gp(rsp))
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		return 1;  /* Yes, a no-CBs CPU needs one. */
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	if (!rdp->nxttail[RCU_NEXT_TAIL])
		return 0;  /* No, this is a no-CBs (or offline) CPU. */
	if (*rdp->nxttail[RCU_NEXT_READY_TAIL])
		return 1;  /* Yes, this CPU has newly registered callbacks. */
	for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++)
		if (rdp->nxttail[i - 1] != rdp->nxttail[i] &&
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		    ULONG_CMP_LT(READ_ONCE(rsp->completed),
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				 rdp->nxtcompleted[i]))
			return 1;  /* Yes, CBs for future grace period. */
	return 0; /* No grace period needed. */
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}

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/*
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 * rcu_eqs_enter_common - current CPU is moving towards extended quiescent state
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 *
 * If the new value of the ->dynticks_nesting counter now is zero,
 * we really have entered idle, and must do the appropriate accounting.
 * The caller must have disabled interrupts.
 */
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static void rcu_eqs_enter_common(long long oldval, bool user)
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{
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	struct rcu_state *rsp;
	struct rcu_data *rdp;
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	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
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	trace_rcu_dyntick(TPS("Start"), oldval, rdtp->dynticks_nesting);
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	if (!user && !is_idle_task(current)) {
589 590
		struct task_struct *idle __maybe_unused =
			idle_task(smp_processor_id());
591

592
		trace_rcu_dyntick(TPS("Error on entry: not idle task"), oldval, 0);
593
		ftrace_dump(DUMP_ORIG);
594 595 596
		WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
			  current->pid, current->comm,
			  idle->pid, idle->comm); /* must be idle task! */
597
	}
598 599 600 601
	for_each_rcu_flavor(rsp) {
		rdp = this_cpu_ptr(rsp->rda);
		do_nocb_deferred_wakeup(rdp);
	}
602
	rcu_prepare_for_idle();
603
	/* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
604
	smp_mb__before_atomic();  /* See above. */
605
	atomic_inc(&rdtp->dynticks);
606
	smp_mb__after_atomic();  /* Force ordering with next sojourn. */
607
	WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
608
	rcu_dynticks_task_enter();
609 610

	/*
611
	 * It is illegal to enter an extended quiescent state while
612 613 614 615 616 617 618 619
	 * in an RCU read-side critical section.
	 */
	rcu_lockdep_assert(!lock_is_held(&rcu_lock_map),
			   "Illegal idle entry in RCU read-side critical section.");
	rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map),
			   "Illegal idle entry in RCU-bh read-side critical section.");
	rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map),
			   "Illegal idle entry in RCU-sched read-side critical section.");
620
}
621

622 623 624
/*
 * Enter an RCU extended quiescent state, which can be either the
 * idle loop or adaptive-tickless usermode execution.
625
 */
626
static void rcu_eqs_enter(bool user)
627
{
628
	long long oldval;
629 630
	struct rcu_dynticks *rdtp;

631
	rdtp = this_cpu_ptr(&rcu_dynticks);
632
	oldval = rdtp->dynticks_nesting;
633
	WARN_ON_ONCE((oldval & DYNTICK_TASK_NEST_MASK) == 0);
634
	if ((oldval & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE) {
635
		rdtp->dynticks_nesting = 0;
636
		rcu_eqs_enter_common(oldval, user);
637
	} else {
638
		rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE;
639
	}
640
}
641 642 643 644 645 646 647 648 649 650 651 652 653 654 655

/**
 * rcu_idle_enter - inform RCU that current CPU is entering idle
 *
 * Enter idle mode, in other words, -leave- the mode in which RCU
 * read-side critical sections can occur.  (Though RCU read-side
 * critical sections can occur in irq handlers in idle, a possibility
 * handled by irq_enter() and irq_exit().)
 *
 * We crowbar the ->dynticks_nesting field to zero to allow for
 * the possibility of usermode upcalls having messed up our count
 * of interrupt nesting level during the prior busy period.
 */
void rcu_idle_enter(void)
{
656 657 658
	unsigned long flags;

	local_irq_save(flags);
659
	rcu_eqs_enter(false);
660
	rcu_sysidle_enter(0);
661
	local_irq_restore(flags);
662
}
663
EXPORT_SYMBOL_GPL(rcu_idle_enter);
664

665
#ifdef CONFIG_RCU_USER_QS
666 667 668 669 670 671 672 673 674 675
/**
 * rcu_user_enter - inform RCU that we are resuming userspace.
 *
 * Enter RCU idle mode right before resuming userspace.  No use of RCU
 * is permitted between this call and rcu_user_exit(). This way the
 * CPU doesn't need to maintain the tick for RCU maintenance purposes
 * when the CPU runs in userspace.
 */
void rcu_user_enter(void)
{
676
	rcu_eqs_enter(1);
677
}
678
#endif /* CONFIG_RCU_USER_QS */
679

680 681 682 683 684 685
/**
 * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
 *
 * Exit from an interrupt handler, which might possibly result in entering
 * idle mode, in other words, leaving the mode in which read-side critical
 * sections can occur.
686
 *
687 688 689 690 691 692 693 694
 * This code assumes that the idle loop never does anything that might
 * result in unbalanced calls to irq_enter() and irq_exit().  If your
 * architecture violates this assumption, RCU will give you what you
 * deserve, good and hard.  But very infrequently and irreproducibly.
 *
 * Use things like work queues to work around this limitation.
 *
 * You have been warned.
695
 */
696
void rcu_irq_exit(void)
697 698
{
	unsigned long flags;
699
	long long oldval;
700 701 702
	struct rcu_dynticks *rdtp;

	local_irq_save(flags);
703
	rdtp = this_cpu_ptr(&rcu_dynticks);
704
	oldval = rdtp->dynticks_nesting;
705 706
	rdtp->dynticks_nesting--;
	WARN_ON_ONCE(rdtp->dynticks_nesting < 0);
707
	if (rdtp->dynticks_nesting)
708
		trace_rcu_dyntick(TPS("--="), oldval, rdtp->dynticks_nesting);
709
	else
710 711
		rcu_eqs_enter_common(oldval, true);
	rcu_sysidle_enter(1);
712 713 714 715
	local_irq_restore(flags);
}

/*
716
 * rcu_eqs_exit_common - current CPU moving away from extended quiescent state
717 718 719 720 721
 *
 * If the new value of the ->dynticks_nesting counter was previously zero,
 * we really have exited idle, and must do the appropriate accounting.
 * The caller must have disabled interrupts.
 */
722
static void rcu_eqs_exit_common(long long oldval, int user)
723
{
724 725
	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);

726
	rcu_dynticks_task_exit();
727
	smp_mb__before_atomic();  /* Force ordering w/previous sojourn. */
728 729
	atomic_inc(&rdtp->dynticks);
	/* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
730
	smp_mb__after_atomic();  /* See above. */
731
	WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
732
	rcu_cleanup_after_idle();
733
	trace_rcu_dyntick(TPS("End"), oldval, rdtp->dynticks_nesting);
734
	if (!user && !is_idle_task(current)) {
735 736
		struct task_struct *idle __maybe_unused =
			idle_task(smp_processor_id());
737

738
		trace_rcu_dyntick(TPS("Error on exit: not idle task"),
739
				  oldval, rdtp->dynticks_nesting);
740
		ftrace_dump(DUMP_ORIG);
741 742 743
		WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
			  current->pid, current->comm,
			  idle->pid, idle->comm); /* must be idle task! */
744 745 746
	}
}

747 748 749
/*
 * Exit an RCU extended quiescent state, which can be either the
 * idle loop or adaptive-tickless usermode execution.
750
 */
751
static void rcu_eqs_exit(bool user)
752 753 754 755
{
	struct rcu_dynticks *rdtp;
	long long oldval;

756
	rdtp = this_cpu_ptr(&rcu_dynticks);
757
	oldval = rdtp->dynticks_nesting;
758
	WARN_ON_ONCE(oldval < 0);
759
	if (oldval & DYNTICK_TASK_NEST_MASK) {
760
		rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
761
	} else {
762
		rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
763
		rcu_eqs_exit_common(oldval, user);
764
	}
765
}
766 767 768 769 770 771 772 773 774 775 776 777 778 779

/**
 * rcu_idle_exit - inform RCU that current CPU is leaving idle
 *
 * Exit idle mode, in other words, -enter- the mode in which RCU
 * read-side critical sections can occur.
 *
 * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST to
 * allow for the possibility of usermode upcalls messing up our count
 * of interrupt nesting level during the busy period that is just
 * now starting.
 */
void rcu_idle_exit(void)
{
780 781 782
	unsigned long flags;

	local_irq_save(flags);
783
	rcu_eqs_exit(false);
784
	rcu_sysidle_exit(0);
785
	local_irq_restore(flags);
786
}
787
EXPORT_SYMBOL_GPL(rcu_idle_exit);
788

789
#ifdef CONFIG_RCU_USER_QS
790 791 792 793 794 795 796 797
/**
 * rcu_user_exit - inform RCU that we are exiting userspace.
 *
 * Exit RCU idle mode while entering the kernel because it can
 * run a RCU read side critical section anytime.
 */
void rcu_user_exit(void)
{
798
	rcu_eqs_exit(1);
799
}
800
#endif /* CONFIG_RCU_USER_QS */
801

802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827
/**
 * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
 *
 * Enter an interrupt handler, which might possibly result in exiting
 * idle mode, in other words, entering the mode in which read-side critical
 * sections can occur.
 *
 * Note that the Linux kernel is fully capable of entering an interrupt
 * handler that it never exits, for example when doing upcalls to
 * user mode!  This code assumes that the idle loop never does upcalls to
 * user mode.  If your architecture does do upcalls from the idle loop (or
 * does anything else that results in unbalanced calls to the irq_enter()
 * and irq_exit() functions), RCU will give you what you deserve, good
 * and hard.  But very infrequently and irreproducibly.
 *
 * Use things like work queues to work around this limitation.
 *
 * You have been warned.
 */
void rcu_irq_enter(void)
{
	unsigned long flags;
	struct rcu_dynticks *rdtp;
	long long oldval;

	local_irq_save(flags);
828
	rdtp = this_cpu_ptr(&rcu_dynticks);
829 830 831
	oldval = rdtp->dynticks_nesting;
	rdtp->dynticks_nesting++;
	WARN_ON_ONCE(rdtp->dynticks_nesting == 0);
832
	if (oldval)
833
		trace_rcu_dyntick(TPS("++="), oldval, rdtp->dynticks_nesting);
834
	else
835 836
		rcu_eqs_exit_common(oldval, true);
	rcu_sysidle_exit(1);
837 838 839 840 841 842
	local_irq_restore(flags);
}

/**
 * rcu_nmi_enter - inform RCU of entry to NMI context
 *
843 844 845 846 847
 * If the CPU was idle from RCU's viewpoint, update rdtp->dynticks and
 * rdtp->dynticks_nmi_nesting to let the RCU grace-period handling know
 * that the CPU is active.  This implementation permits nested NMIs, as
 * long as the nesting level does not overflow an int.  (You will probably
 * run out of stack space first.)
848 849 850
 */
void rcu_nmi_enter(void)
{
851
	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
852
	int incby = 2;
853

854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874
	/* Complain about underflow. */
	WARN_ON_ONCE(rdtp->dynticks_nmi_nesting < 0);

	/*
	 * If idle from RCU viewpoint, atomically increment ->dynticks
	 * to mark non-idle and increment ->dynticks_nmi_nesting by one.
	 * Otherwise, increment ->dynticks_nmi_nesting by two.  This means
	 * if ->dynticks_nmi_nesting is equal to one, we are guaranteed
	 * to be in the outermost NMI handler that interrupted an RCU-idle
	 * period (observation due to Andy Lutomirski).
	 */
	if (!(atomic_read(&rdtp->dynticks) & 0x1)) {
		smp_mb__before_atomic();  /* Force delay from prior write. */
		atomic_inc(&rdtp->dynticks);
		/* atomic_inc() before later RCU read-side crit sects */
		smp_mb__after_atomic();  /* See above. */
		WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
		incby = 1;
	}
	rdtp->dynticks_nmi_nesting += incby;
	barrier();
875 876 877 878 879
}

/**
 * rcu_nmi_exit - inform RCU of exit from NMI context
 *
880 881 882 883
 * If we are returning from the outermost NMI handler that interrupted an
 * RCU-idle period, update rdtp->dynticks and rdtp->dynticks_nmi_nesting
 * to let the RCU grace-period handling know that the CPU is back to
 * being RCU-idle.
884 885 886
 */
void rcu_nmi_exit(void)
{
887
	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
888

889 890 891 892 893 894 895 896 897 898 899 900 901 902
	/*
	 * Check for ->dynticks_nmi_nesting underflow and bad ->dynticks.
	 * (We are exiting an NMI handler, so RCU better be paying attention
	 * to us!)
	 */
	WARN_ON_ONCE(rdtp->dynticks_nmi_nesting <= 0);
	WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));

	/*
	 * If the nesting level is not 1, the CPU wasn't RCU-idle, so
	 * leave it in non-RCU-idle state.
	 */
	if (rdtp->dynticks_nmi_nesting != 1) {
		rdtp->dynticks_nmi_nesting -= 2;
903
		return;
904 905 906 907
	}

	/* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
	rdtp->dynticks_nmi_nesting = 0;
908
	/* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
909
	smp_mb__before_atomic();  /* See above. */
910
	atomic_inc(&rdtp->dynticks);
911
	smp_mb__after_atomic();  /* Force delay to next write. */
912
	WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
913 914 915
}

/**
916 917 918 919 920 921 922
 * __rcu_is_watching - are RCU read-side critical sections safe?
 *
 * Return true if RCU is watching the running CPU, which means that
 * this CPU can safely enter RCU read-side critical sections.  Unlike
 * rcu_is_watching(), the caller of __rcu_is_watching() must have at
 * least disabled preemption.
 */
923
bool notrace __rcu_is_watching(void)
924 925 926 927 928 929
{
	return atomic_read(this_cpu_ptr(&rcu_dynticks.dynticks)) & 0x1;
}

/**
 * rcu_is_watching - see if RCU thinks that the current CPU is idle
930
 *
931
 * If the current CPU is in its idle loop and is neither in an interrupt
932
 * or NMI handler, return true.
933
 */
934
bool notrace rcu_is_watching(void)
935
{
936
	bool ret;
937 938

	preempt_disable();
939
	ret = __rcu_is_watching();
940 941
	preempt_enable();
	return ret;
942
}
943
EXPORT_SYMBOL_GPL(rcu_is_watching);
944

945
#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
946 947 948 949 950 951 952

/*
 * Is the current CPU online?  Disable preemption to avoid false positives
 * that could otherwise happen due to the current CPU number being sampled,
 * this task being preempted, its old CPU being taken offline, resuming
 * on some other CPU, then determining that its old CPU is now offline.
 * It is OK to use RCU on an offline processor during initial boot, hence
953 954 955 956 957 958 959 960 961 962 963
 * the check for rcu_scheduler_fully_active.  Note also that it is OK
 * for a CPU coming online to use RCU for one jiffy prior to marking itself
 * online in the cpu_online_mask.  Similarly, it is OK for a CPU going
 * offline to continue to use RCU for one jiffy after marking itself
 * offline in the cpu_online_mask.  This leniency is necessary given the
 * non-atomic nature of the online and offline processing, for example,
 * the fact that a CPU enters the scheduler after completing the CPU_DYING
 * notifiers.
 *
 * This is also why RCU internally marks CPUs online during the
 * CPU_UP_PREPARE phase and offline during the CPU_DEAD phase.
964 965 966 967 968 969
 *
 * Disable checking if in an NMI handler because we cannot safely report
 * errors from NMI handlers anyway.
 */
bool rcu_lockdep_current_cpu_online(void)
{
970 971
	struct rcu_data *rdp;
	struct rcu_node *rnp;
972 973 974
	bool ret;

	if (in_nmi())
F
Fengguang Wu 已提交
975
		return true;
976
	preempt_disable();
977
	rdp = this_cpu_ptr(&rcu_sched_data);
978
	rnp = rdp->mynode;
979
	ret = (rdp->grpmask & rcu_rnp_online_cpus(rnp)) ||
980 981 982 983 984 985
	      !rcu_scheduler_fully_active;
	preempt_enable();
	return ret;
}
EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);

986
#endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
987

988
/**
989
 * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle
990
 *
991 992 993
 * If the current CPU is idle or running at a first-level (not nested)
 * interrupt from idle, return true.  The caller must have at least
 * disabled preemption.
994
 */
995
static int rcu_is_cpu_rrupt_from_idle(void)
996
{
997
	return __this_cpu_read(rcu_dynticks.dynticks_nesting) <= 1;
998 999 1000 1001 1002
}

/*
 * Snapshot the specified CPU's dynticks counter so that we can later
 * credit them with an implicit quiescent state.  Return 1 if this CPU
1003
 * is in dynticks idle mode, which is an extended quiescent state.
1004
 */
1005 1006
static int dyntick_save_progress_counter(struct rcu_data *rdp,
					 bool *isidle, unsigned long *maxj)
1007
{
1008
	rdp->dynticks_snap = atomic_add_return(0, &rdp->dynticks->dynticks);
1009
	rcu_sysidle_check_cpu(rdp, isidle, maxj);
1010 1011 1012 1013
	if ((rdp->dynticks_snap & 0x1) == 0) {
		trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
		return 1;
	} else {
1014
		if (ULONG_CMP_LT(READ_ONCE(rdp->gpnum) + ULONG_MAX / 4,
1015
				 rdp->mynode->gpnum))
1016
			WRITE_ONCE(rdp->gpwrap, true);
1017 1018
		return 0;
	}
1019 1020 1021 1022 1023 1024
}

/*
 * Return true if the specified CPU has passed through a quiescent
 * state by virtue of being in or having passed through an dynticks
 * idle state since the last call to dyntick_save_progress_counter()
1025
 * for this same CPU, or by virtue of having been offline.
1026
 */
1027 1028
static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
				    bool *isidle, unsigned long *maxj)
1029
{
1030
	unsigned int curr;
1031
	int *rcrmp;
1032
	unsigned int snap;
1033

1034 1035
	curr = (unsigned int)atomic_add_return(0, &rdp->dynticks->dynticks);
	snap = (unsigned int)rdp->dynticks_snap;
1036 1037 1038 1039 1040 1041 1042 1043 1044

	/*
	 * If the CPU passed through or entered a dynticks idle phase with
	 * no active irq/NMI handlers, then we can safely pretend that the CPU
	 * already acknowledged the request to pass through a quiescent
	 * state.  Either way, that CPU cannot possibly be in an RCU
	 * read-side critical section that started before the beginning
	 * of the current RCU grace period.
	 */
1045
	if ((curr & 0x1) == 0 || UINT_CMP_GE(curr, snap + 2)) {
1046
		trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
1047 1048 1049 1050
		rdp->dynticks_fqs++;
		return 1;
	}

1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065
	/*
	 * Check for the CPU being offline, but only if the grace period
	 * is old enough.  We don't need to worry about the CPU changing
	 * state: If we see it offline even once, it has been through a
	 * quiescent state.
	 *
	 * The reason for insisting that the grace period be at least
	 * one jiffy old is that CPUs that are not quite online and that
	 * have just gone offline can still execute RCU read-side critical
	 * sections.
	 */
	if (ULONG_CMP_GE(rdp->rsp->gp_start + 2, jiffies))
		return 0;  /* Grace period is not old enough. */
	barrier();
	if (cpu_is_offline(rdp->cpu)) {
1066
		trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("ofl"));
1067 1068 1069
		rdp->offline_fqs++;
		return 1;
	}
1070 1071

	/*
1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090
	 * A CPU running for an extended time within the kernel can
	 * delay RCU grace periods.  When the CPU is in NO_HZ_FULL mode,
	 * even context-switching back and forth between a pair of
	 * in-kernel CPU-bound tasks cannot advance grace periods.
	 * So if the grace period is old enough, make the CPU pay attention.
	 * Note that the unsynchronized assignments to the per-CPU
	 * rcu_sched_qs_mask variable are safe.  Yes, setting of
	 * bits can be lost, but they will be set again on the next
	 * force-quiescent-state pass.  So lost bit sets do not result
	 * in incorrect behavior, merely in a grace period lasting
	 * a few jiffies longer than it might otherwise.  Because
	 * there are at most four threads involved, and because the
	 * updates are only once every few jiffies, the probability of
	 * lossage (and thus of slight grace-period extension) is
	 * quite low.
	 *
	 * Note that if the jiffies_till_sched_qs boot/sysfs parameter
	 * is set too high, we override with half of the RCU CPU stall
	 * warning delay.
1091
	 */
1092 1093 1094
	rcrmp = &per_cpu(rcu_sched_qs_mask, rdp->cpu);
	if (ULONG_CMP_GE(jiffies,
			 rdp->rsp->gp_start + jiffies_till_sched_qs) ||
1095
	    ULONG_CMP_GE(jiffies, rdp->rsp->jiffies_resched)) {
1096 1097 1098
		if (!(READ_ONCE(*rcrmp) & rdp->rsp->flavor_mask)) {
			WRITE_ONCE(rdp->cond_resched_completed,
				   READ_ONCE(rdp->mynode->completed));
1099
			smp_mb(); /* ->cond_resched_completed before *rcrmp. */
1100 1101
			WRITE_ONCE(*rcrmp,
				   READ_ONCE(*rcrmp) + rdp->rsp->flavor_mask);
1102 1103 1104 1105 1106 1107 1108
			resched_cpu(rdp->cpu);  /* Force CPU into scheduler. */
			rdp->rsp->jiffies_resched += 5; /* Enable beating. */
		} else if (ULONG_CMP_GE(jiffies, rdp->rsp->jiffies_resched)) {
			/* Time to beat on that CPU again! */
			resched_cpu(rdp->cpu);  /* Force CPU into scheduler. */
			rdp->rsp->jiffies_resched += 5; /* Re-enable beating. */
		}
1109 1110
	}

1111
	return 0;
1112 1113 1114 1115
}

static void record_gp_stall_check_time(struct rcu_state *rsp)
{
1116
	unsigned long j = jiffies;
1117
	unsigned long j1;
1118 1119 1120

	rsp->gp_start = j;
	smp_wmb(); /* Record start time before stall time. */
1121
	j1 = rcu_jiffies_till_stall_check();
1122
	WRITE_ONCE(rsp->jiffies_stall, j + j1);
1123
	rsp->jiffies_resched = j + j1 / 2;
1124
	rsp->n_force_qs_gpstart = READ_ONCE(rsp->n_force_qs);
1125 1126
}

1127 1128 1129 1130 1131 1132 1133 1134 1135
/*
 * Complain about starvation of grace-period kthread.
 */
static void rcu_check_gp_kthread_starvation(struct rcu_state *rsp)
{
	unsigned long gpa;
	unsigned long j;

	j = jiffies;
1136
	gpa = READ_ONCE(rsp->gp_activity);
1137 1138 1139
	if (j - gpa > 2 * HZ)
		pr_err("%s kthread starved for %ld jiffies!\n",
		       rsp->name, j - gpa);
1140 1141
}

1142
/*
1143
 * Dump stacks of all tasks running on stalled CPUs.
1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161
 */
static void rcu_dump_cpu_stacks(struct rcu_state *rsp)
{
	int cpu;
	unsigned long flags;
	struct rcu_node *rnp;

	rcu_for_each_leaf_node(rsp, rnp) {
		raw_spin_lock_irqsave(&rnp->lock, flags);
		if (rnp->qsmask != 0) {
			for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
				if (rnp->qsmask & (1UL << cpu))
					dump_cpu_task(rnp->grplo + cpu);
		}
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
	}
}

1162
static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum)
1163 1164 1165 1166
{
	int cpu;
	long delta;
	unsigned long flags;
1167 1168
	unsigned long gpa;
	unsigned long j;
1169
	int ndetected = 0;
1170
	struct rcu_node *rnp = rcu_get_root(rsp);
1171
	long totqlen = 0;
1172 1173 1174

	/* Only let one CPU complain about others per time interval. */

P
Paul E. McKenney 已提交
1175
	raw_spin_lock_irqsave(&rnp->lock, flags);
1176
	delta = jiffies - READ_ONCE(rsp->jiffies_stall);
1177
	if (delta < RCU_STALL_RAT_DELAY || !rcu_gp_in_progress(rsp)) {
P
Paul E. McKenney 已提交
1178
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
1179 1180
		return;
	}
1181 1182
	WRITE_ONCE(rsp->jiffies_stall,
		   jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
P
Paul E. McKenney 已提交
1183
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
1184

1185 1186 1187 1188 1189
	/*
	 * OK, time to rat on our buddy...
	 * See Documentation/RCU/stallwarn.txt for info on how to debug
	 * RCU CPU stall warnings.
	 */
1190
	pr_err("INFO: %s detected stalls on CPUs/tasks:",
1191
	       rsp->name);
1192
	print_cpu_stall_info_begin();
1193
	rcu_for_each_leaf_node(rsp, rnp) {
1194
		raw_spin_lock_irqsave(&rnp->lock, flags);
1195
		ndetected += rcu_print_task_stall(rnp);
1196 1197 1198 1199 1200 1201 1202 1203
		if (rnp->qsmask != 0) {
			for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
				if (rnp->qsmask & (1UL << cpu)) {
					print_cpu_stall_info(rsp,
							     rnp->grplo + cpu);
					ndetected++;
				}
		}
1204
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
1205
	}
1206 1207

	print_cpu_stall_info_end();
1208 1209
	for_each_possible_cpu(cpu)
		totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen;
1210
	pr_cont("(detected by %d, t=%ld jiffies, g=%ld, c=%ld, q=%lu)\n",
1211
	       smp_processor_id(), (long)(jiffies - rsp->gp_start),
1212
	       (long)rsp->gpnum, (long)rsp->completed, totqlen);
1213
	if (ndetected) {
1214
		rcu_dump_cpu_stacks(rsp);
1215
	} else {
1216 1217
		if (READ_ONCE(rsp->gpnum) != gpnum ||
		    READ_ONCE(rsp->completed) == gpnum) {
1218 1219 1220
			pr_err("INFO: Stall ended before state dump start\n");
		} else {
			j = jiffies;
1221
			gpa = READ_ONCE(rsp->gp_activity);
1222
			pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld, root ->qsmask %#lx\n",
1223
			       rsp->name, j - gpa, j, gpa,
1224 1225
			       jiffies_till_next_fqs,
			       rcu_get_root(rsp)->qsmask);
1226 1227 1228 1229
			/* In this case, the current CPU might be at fault. */
			sched_show_task(current);
		}
	}
1230

1231
	/* Complain about tasks blocking the grace period. */
1232 1233
	rcu_print_detail_task_stall(rsp);

1234 1235
	rcu_check_gp_kthread_starvation(rsp);

1236
	force_quiescent_state(rsp);  /* Kick them all. */
1237 1238 1239 1240
}

static void print_cpu_stall(struct rcu_state *rsp)
{
1241
	int cpu;
1242 1243
	unsigned long flags;
	struct rcu_node *rnp = rcu_get_root(rsp);
1244
	long totqlen = 0;
1245

1246 1247 1248 1249 1250
	/*
	 * OK, time to rat on ourselves...
	 * See Documentation/RCU/stallwarn.txt for info on how to debug
	 * RCU CPU stall warnings.
	 */
1251
	pr_err("INFO: %s self-detected stall on CPU", rsp->name);
1252 1253 1254
	print_cpu_stall_info_begin();
	print_cpu_stall_info(rsp, smp_processor_id());
	print_cpu_stall_info_end();
1255 1256
	for_each_possible_cpu(cpu)
		totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen;
1257 1258 1259
	pr_cont(" (t=%lu jiffies g=%ld c=%ld q=%lu)\n",
		jiffies - rsp->gp_start,
		(long)rsp->gpnum, (long)rsp->completed, totqlen);
1260 1261 1262

	rcu_check_gp_kthread_starvation(rsp);

1263
	rcu_dump_cpu_stacks(rsp);
1264

P
Paul E. McKenney 已提交
1265
	raw_spin_lock_irqsave(&rnp->lock, flags);
1266 1267 1268
	if (ULONG_CMP_GE(jiffies, READ_ONCE(rsp->jiffies_stall)))
		WRITE_ONCE(rsp->jiffies_stall,
			   jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
P
Paul E. McKenney 已提交
1269
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
1270

1271 1272 1273 1274 1275 1276 1277 1278
	/*
	 * Attempt to revive the RCU machinery by forcing a context switch.
	 *
	 * A context switch would normally allow the RCU state machine to make
	 * progress and it could be we're stuck in kernel space without context
	 * switches for an entirely unreasonable amount of time.
	 */
	resched_cpu(smp_processor_id());
1279 1280 1281 1282
}

static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
{
1283 1284 1285
	unsigned long completed;
	unsigned long gpnum;
	unsigned long gps;
1286 1287
	unsigned long j;
	unsigned long js;
1288 1289
	struct rcu_node *rnp;

1290
	if (rcu_cpu_stall_suppress || !rcu_gp_in_progress(rsp))
1291
		return;
1292
	j = jiffies;
1293 1294 1295 1296 1297 1298 1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309 1310

	/*
	 * Lots of memory barriers to reject false positives.
	 *
	 * The idea is to pick up rsp->gpnum, then rsp->jiffies_stall,
	 * then rsp->gp_start, and finally rsp->completed.  These values
	 * are updated in the opposite order with memory barriers (or
	 * equivalent) during grace-period initialization and cleanup.
	 * Now, a false positive can occur if we get an new value of
	 * rsp->gp_start and a old value of rsp->jiffies_stall.  But given
	 * the memory barriers, the only way that this can happen is if one
	 * grace period ends and another starts between these two fetches.
	 * Detect this by comparing rsp->completed with the previous fetch
	 * from rsp->gpnum.
	 *
	 * Given this check, comparisons of jiffies, rsp->jiffies_stall,
	 * and rsp->gp_start suffice to forestall false positives.
	 */
1311
	gpnum = READ_ONCE(rsp->gpnum);
1312
	smp_rmb(); /* Pick up ->gpnum first... */
1313
	js = READ_ONCE(rsp->jiffies_stall);
1314
	smp_rmb(); /* ...then ->jiffies_stall before the rest... */
1315
	gps = READ_ONCE(rsp->gp_start);
1316
	smp_rmb(); /* ...and finally ->gp_start before ->completed. */
1317
	completed = READ_ONCE(rsp->completed);
1318 1319 1320 1321
	if (ULONG_CMP_GE(completed, gpnum) ||
	    ULONG_CMP_LT(j, js) ||
	    ULONG_CMP_GE(gps, js))
		return; /* No stall or GP completed since entering function. */
1322
	rnp = rdp->mynode;
1323
	if (rcu_gp_in_progress(rsp) &&
1324
	    (READ_ONCE(rnp->qsmask) & rdp->grpmask)) {
1325 1326 1327 1328

		/* We haven't checked in, so go dump stack. */
		print_cpu_stall(rsp);

1329 1330
	} else if (rcu_gp_in_progress(rsp) &&
		   ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY)) {
1331

1332
		/* They had a few time units to dump stack, so complain. */
1333
		print_other_cpu_stall(rsp, gpnum);
1334 1335 1336
	}
}

1337 1338 1339 1340 1341 1342 1343 1344 1345 1346 1347
/**
 * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
 *
 * Set the stall-warning timeout way off into the future, thus preventing
 * any RCU CPU stall-warning messages from appearing in the current set of
 * RCU grace periods.
 *
 * The caller must disable hard irqs.
 */
void rcu_cpu_stall_reset(void)
{
1348 1349 1350
	struct rcu_state *rsp;

	for_each_rcu_flavor(rsp)
1351
		WRITE_ONCE(rsp->jiffies_stall, jiffies + ULONG_MAX / 2);
1352 1353
}

1354
/*
1355 1356 1357
 * Initialize the specified rcu_data structure's default callback list
 * to empty.  The default callback list is the one that is not used by
 * no-callbacks CPUs.
1358
 */
1359
static void init_default_callback_list(struct rcu_data *rdp)
1360 1361 1362 1363 1364 1365 1366 1367
{
	int i;

	rdp->nxtlist = NULL;
	for (i = 0; i < RCU_NEXT_SIZE; i++)
		rdp->nxttail[i] = &rdp->nxtlist;
}

1368 1369 1370 1371 1372 1373 1374 1375 1376 1377
/*
 * Initialize the specified rcu_data structure's callback list to empty.
 */
static void init_callback_list(struct rcu_data *rdp)
{
	if (init_nocb_callback_list(rdp))
		return;
	init_default_callback_list(rdp);
}

1378 1379 1380 1381 1382 1383 1384 1385 1386 1387 1388 1389 1390 1391 1392 1393 1394 1395 1396 1397 1398 1399 1400 1401 1402 1403 1404 1405 1406
/*
 * Determine the value that ->completed will have at the end of the
 * next subsequent grace period.  This is used to tag callbacks so that
 * a CPU can invoke callbacks in a timely fashion even if that CPU has
 * been dyntick-idle for an extended period with callbacks under the
 * influence of RCU_FAST_NO_HZ.
 *
 * The caller must hold rnp->lock with interrupts disabled.
 */
static unsigned long rcu_cbs_completed(struct rcu_state *rsp,
				       struct rcu_node *rnp)
{
	/*
	 * If RCU is idle, we just wait for the next grace period.
	 * But we can only be sure that RCU is idle if we are looking
	 * at the root rcu_node structure -- otherwise, a new grace
	 * period might have started, but just not yet gotten around
	 * to initializing the current non-root rcu_node structure.
	 */
	if (rcu_get_root(rsp) == rnp && rnp->gpnum == rnp->completed)
		return rnp->completed + 1;

	/*
	 * Otherwise, wait for a possible partial grace period and
	 * then the subsequent full grace period.
	 */
	return rnp->completed + 2;
}

1407 1408 1409 1410 1411
/*
 * Trace-event helper function for rcu_start_future_gp() and
 * rcu_nocb_wait_gp().
 */
static void trace_rcu_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
1412
				unsigned long c, const char *s)
1413 1414 1415 1416 1417 1418 1419 1420 1421
{
	trace_rcu_future_grace_period(rdp->rsp->name, rnp->gpnum,
				      rnp->completed, c, rnp->level,
				      rnp->grplo, rnp->grphi, s);
}

/*
 * Start some future grace period, as needed to handle newly arrived
 * callbacks.  The required future grace periods are recorded in each
1422 1423
 * rcu_node structure's ->need_future_gp field.  Returns true if there
 * is reason to awaken the grace-period kthread.
1424 1425 1426
 *
 * The caller must hold the specified rcu_node structure's ->lock.
 */
1427 1428 1429
static bool __maybe_unused
rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
		    unsigned long *c_out)
1430 1431 1432
{
	unsigned long c;
	int i;
1433
	bool ret = false;
1434 1435 1436 1437 1438 1439 1440
	struct rcu_node *rnp_root = rcu_get_root(rdp->rsp);

	/*
	 * Pick up grace-period number for new callbacks.  If this
	 * grace period is already marked as needed, return to the caller.
	 */
	c = rcu_cbs_completed(rdp->rsp, rnp);
1441
	trace_rcu_future_gp(rnp, rdp, c, TPS("Startleaf"));
1442
	if (rnp->need_future_gp[c & 0x1]) {
1443
		trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartleaf"));
1444
		goto out;
1445 1446 1447 1448 1449 1450 1451
	}

	/*
	 * If either this rcu_node structure or the root rcu_node structure
	 * believe that a grace period is in progress, then we must wait
	 * for the one following, which is in "c".  Because our request
	 * will be noticed at the end of the current grace period, we don't
1452 1453 1454 1455 1456 1457 1458
	 * need to explicitly start one.  We only do the lockless check
	 * of rnp_root's fields if the current rcu_node structure thinks
	 * there is no grace period in flight, and because we hold rnp->lock,
	 * the only possible change is when rnp_root's two fields are
	 * equal, in which case rnp_root->gpnum might be concurrently
	 * incremented.  But that is OK, as it will just result in our
	 * doing some extra useless work.
1459 1460
	 */
	if (rnp->gpnum != rnp->completed ||
1461
	    READ_ONCE(rnp_root->gpnum) != READ_ONCE(rnp_root->completed)) {
1462
		rnp->need_future_gp[c & 0x1]++;
1463
		trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleaf"));
1464
		goto out;
1465 1466 1467 1468 1469 1470 1471
	}

	/*
	 * There might be no grace period in progress.  If we don't already
	 * hold it, acquire the root rcu_node structure's lock in order to
	 * start one (if needed).
	 */
1472
	if (rnp != rnp_root) {
1473
		raw_spin_lock(&rnp_root->lock);
1474 1475
		smp_mb__after_unlock_lock();
	}
1476 1477 1478 1479 1480 1481 1482 1483 1484 1485 1486 1487 1488 1489 1490 1491 1492

	/*
	 * Get a new grace-period number.  If there really is no grace
	 * period in progress, it will be smaller than the one we obtained
	 * earlier.  Adjust callbacks as needed.  Note that even no-CBs
	 * CPUs have a ->nxtcompleted[] array, so no no-CBs checks needed.
	 */
	c = rcu_cbs_completed(rdp->rsp, rnp_root);
	for (i = RCU_DONE_TAIL; i < RCU_NEXT_TAIL; i++)
		if (ULONG_CMP_LT(c, rdp->nxtcompleted[i]))
			rdp->nxtcompleted[i] = c;

	/*
	 * If the needed for the required grace period is already
	 * recorded, trace and leave.
	 */
	if (rnp_root->need_future_gp[c & 0x1]) {
1493
		trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartedroot"));
1494 1495 1496 1497 1498 1499 1500 1501
		goto unlock_out;
	}

	/* Record the need for the future grace period. */
	rnp_root->need_future_gp[c & 0x1]++;

	/* If a grace period is not already in progress, start one. */
	if (rnp_root->gpnum != rnp_root->completed) {
1502
		trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleafroot"));
1503
	} else {
1504
		trace_rcu_future_gp(rnp, rdp, c, TPS("Startedroot"));
1505
		ret = rcu_start_gp_advanced(rdp->rsp, rnp_root, rdp);
1506 1507 1508 1509
	}
unlock_out:
	if (rnp != rnp_root)
		raw_spin_unlock(&rnp_root->lock);
1510 1511 1512 1513
out:
	if (c_out != NULL)
		*c_out = c;
	return ret;
1514 1515 1516 1517 1518 1519 1520 1521 1522 1523 1524 1525 1526 1527 1528 1529 1530
}

/*
 * Clean up any old requests for the just-ended grace period.  Also return
 * whether any additional grace periods have been requested.  Also invoke
 * rcu_nocb_gp_cleanup() in order to wake up any no-callbacks kthreads
 * waiting for this grace period to complete.
 */
static int rcu_future_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
{
	int c = rnp->completed;
	int needmore;
	struct rcu_data *rdp = this_cpu_ptr(rsp->rda);

	rcu_nocb_gp_cleanup(rsp, rnp);
	rnp->need_future_gp[c & 0x1] = 0;
	needmore = rnp->need_future_gp[(c + 1) & 0x1];
1531 1532
	trace_rcu_future_gp(rnp, rdp, c,
			    needmore ? TPS("CleanupMore") : TPS("Cleanup"));
1533 1534 1535
	return needmore;
}

1536 1537 1538 1539 1540 1541 1542 1543 1544 1545
/*
 * Awaken the grace-period kthread for the specified flavor of RCU.
 * Don't do a self-awaken, and don't bother awakening when there is
 * nothing for the grace-period kthread to do (as in several CPUs
 * raced to awaken, and we lost), and finally don't try to awaken
 * a kthread that has not yet been created.
 */
static void rcu_gp_kthread_wake(struct rcu_state *rsp)
{
	if (current == rsp->gp_kthread ||
1546
	    !READ_ONCE(rsp->gp_flags) ||
1547 1548 1549 1550 1551
	    !rsp->gp_kthread)
		return;
	wake_up(&rsp->gp_wq);
}

1552 1553 1554 1555 1556 1557 1558
/*
 * If there is room, assign a ->completed number to any callbacks on
 * this CPU that have not already been assigned.  Also accelerate any
 * callbacks that were previously assigned a ->completed number that has
 * since proven to be too conservative, which can happen if callbacks get
 * assigned a ->completed number while RCU is idle, but with reference to
 * a non-root rcu_node structure.  This function is idempotent, so it does
1559 1560
 * not hurt to call it repeatedly.  Returns an flag saying that we should
 * awaken the RCU grace-period kthread.
1561 1562 1563
 *
 * The caller must hold rnp->lock with interrupts disabled.
 */
1564
static bool rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
1565 1566 1567 1568
			       struct rcu_data *rdp)
{
	unsigned long c;
	int i;
1569
	bool ret;
1570 1571 1572

	/* If the CPU has no callbacks, nothing to do. */
	if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL])
1573
		return false;
1574 1575 1576 1577 1578 1579 1580 1581 1582 1583 1584 1585 1586 1587 1588 1589 1590 1591 1592 1593 1594 1595 1596 1597 1598 1599 1600 1601

	/*
	 * Starting from the sublist containing the callbacks most
	 * recently assigned a ->completed number and working down, find the
	 * first sublist that is not assignable to an upcoming grace period.
	 * Such a sublist has something in it (first two tests) and has
	 * a ->completed number assigned that will complete sooner than
	 * the ->completed number for newly arrived callbacks (last test).
	 *
	 * The key point is that any later sublist can be assigned the
	 * same ->completed number as the newly arrived callbacks, which
	 * means that the callbacks in any of these later sublist can be
	 * grouped into a single sublist, whether or not they have already
	 * been assigned a ->completed number.
	 */
	c = rcu_cbs_completed(rsp, rnp);
	for (i = RCU_NEXT_TAIL - 1; i > RCU_DONE_TAIL; i--)
		if (rdp->nxttail[i] != rdp->nxttail[i - 1] &&
		    !ULONG_CMP_GE(rdp->nxtcompleted[i], c))
			break;

	/*
	 * If there are no sublist for unassigned callbacks, leave.
	 * At the same time, advance "i" one sublist, so that "i" will
	 * index into the sublist where all the remaining callbacks should
	 * be grouped into.
	 */
	if (++i >= RCU_NEXT_TAIL)
1602
		return false;
1603 1604 1605 1606 1607 1608 1609 1610 1611 1612

	/*
	 * Assign all subsequent callbacks' ->completed number to the next
	 * full grace period and group them all in the sublist initially
	 * indexed by "i".
	 */
	for (; i <= RCU_NEXT_TAIL; i++) {
		rdp->nxttail[i] = rdp->nxttail[RCU_NEXT_TAIL];
		rdp->nxtcompleted[i] = c;
	}
1613
	/* Record any needed additional grace periods. */
1614
	ret = rcu_start_future_gp(rnp, rdp, NULL);
1615 1616 1617

	/* Trace depending on how much we were able to accelerate. */
	if (!*rdp->nxttail[RCU_WAIT_TAIL])
1618
		trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccWaitCB"));
1619
	else
1620
		trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccReadyCB"));
1621
	return ret;
1622 1623 1624 1625 1626 1627 1628 1629
}

/*
 * Move any callbacks whose grace period has completed to the
 * RCU_DONE_TAIL sublist, then compact the remaining sublists and
 * assign ->completed numbers to any callbacks in the RCU_NEXT_TAIL
 * sublist.  This function is idempotent, so it does not hurt to
 * invoke it repeatedly.  As long as it is not invoked -too- often...
1630
 * Returns true if the RCU grace-period kthread needs to be awakened.
1631 1632 1633
 *
 * The caller must hold rnp->lock with interrupts disabled.
 */
1634
static bool rcu_advance_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
1635 1636 1637 1638 1639 1640
			    struct rcu_data *rdp)
{
	int i, j;

	/* If the CPU has no callbacks, nothing to do. */
	if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL])
1641
		return false;
1642 1643 1644 1645 1646 1647 1648 1649 1650 1651 1652 1653 1654 1655 1656 1657 1658 1659 1660 1661 1662 1663 1664

	/*
	 * Find all callbacks whose ->completed numbers indicate that they
	 * are ready to invoke, and put them into the RCU_DONE_TAIL sublist.
	 */
	for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++) {
		if (ULONG_CMP_LT(rnp->completed, rdp->nxtcompleted[i]))
			break;
		rdp->nxttail[RCU_DONE_TAIL] = rdp->nxttail[i];
	}
	/* Clean up any sublist tail pointers that were misordered above. */
	for (j = RCU_WAIT_TAIL; j < i; j++)
		rdp->nxttail[j] = rdp->nxttail[RCU_DONE_TAIL];

	/* Copy down callbacks to fill in empty sublists. */
	for (j = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++, j++) {
		if (rdp->nxttail[j] == rdp->nxttail[RCU_NEXT_TAIL])
			break;
		rdp->nxttail[j] = rdp->nxttail[i];
		rdp->nxtcompleted[j] = rdp->nxtcompleted[i];
	}

	/* Classify any remaining callbacks. */
1665
	return rcu_accelerate_cbs(rsp, rnp, rdp);
1666 1667
}

1668
/*
1669 1670 1671
 * Update CPU-local rcu_data state to record the beginnings and ends of
 * grace periods.  The caller must hold the ->lock of the leaf rcu_node
 * structure corresponding to the current CPU, and must have irqs disabled.
1672
 * Returns true if the grace-period kthread needs to be awakened.
1673
 */
1674 1675
static bool __note_gp_changes(struct rcu_state *rsp, struct rcu_node *rnp,
			      struct rcu_data *rdp)
1676
{
1677 1678
	bool ret;

1679
	/* Handle the ends of any preceding grace periods first. */
1680
	if (rdp->completed == rnp->completed &&
1681
	    !unlikely(READ_ONCE(rdp->gpwrap))) {
1682

1683
		/* No grace period end, so just accelerate recent callbacks. */
1684
		ret = rcu_accelerate_cbs(rsp, rnp, rdp);
1685

1686 1687 1688
	} else {

		/* Advance callbacks. */
1689
		ret = rcu_advance_cbs(rsp, rnp, rdp);
1690 1691 1692

		/* Remember that we saw this grace-period completion. */
		rdp->completed = rnp->completed;
1693
		trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuend"));
1694
	}
1695

1696
	if (rdp->gpnum != rnp->gpnum || unlikely(READ_ONCE(rdp->gpwrap))) {
1697 1698 1699 1700 1701 1702
		/*
		 * If the current grace period is waiting for this CPU,
		 * set up to detect a quiescent state, otherwise don't
		 * go looking for one.
		 */
		rdp->gpnum = rnp->gpnum;
1703
		trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpustart"));
1704
		rdp->passed_quiesce = 0;
1705
		rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_qs_ctr);
1706 1707
		rdp->qs_pending = !!(rnp->qsmask & rdp->grpmask);
		zero_cpu_stall_ticks(rdp);
1708
		WRITE_ONCE(rdp->gpwrap, false);
1709
	}
1710
	return ret;
1711 1712
}

1713
static void note_gp_changes(struct rcu_state *rsp, struct rcu_data *rdp)
1714 1715
{
	unsigned long flags;
1716
	bool needwake;
1717 1718 1719 1720
	struct rcu_node *rnp;

	local_irq_save(flags);
	rnp = rdp->mynode;
1721 1722 1723
	if ((rdp->gpnum == READ_ONCE(rnp->gpnum) &&
	     rdp->completed == READ_ONCE(rnp->completed) &&
	     !unlikely(READ_ONCE(rdp->gpwrap))) || /* w/out lock. */
1724 1725 1726 1727
	    !raw_spin_trylock(&rnp->lock)) { /* irqs already off, so later. */
		local_irq_restore(flags);
		return;
	}
1728
	smp_mb__after_unlock_lock();
1729
	needwake = __note_gp_changes(rsp, rnp, rdp);
1730
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
1731 1732
	if (needwake)
		rcu_gp_kthread_wake(rsp);
1733 1734
}

1735
/*
1736
 * Initialize a new grace period.  Return 0 if no grace period required.
1737
 */
1738
static int rcu_gp_init(struct rcu_state *rsp)
1739
{
1740
	unsigned long oldmask;
1741
	struct rcu_data *rdp;
1742
	struct rcu_node *rnp = rcu_get_root(rsp);
1743

1744
	WRITE_ONCE(rsp->gp_activity, jiffies);
1745
	raw_spin_lock_irq(&rnp->lock);
1746
	smp_mb__after_unlock_lock();
1747
	if (!READ_ONCE(rsp->gp_flags)) {
1748 1749 1750 1751
		/* Spurious wakeup, tell caller to go back to sleep.  */
		raw_spin_unlock_irq(&rnp->lock);
		return 0;
	}
1752
	WRITE_ONCE(rsp->gp_flags, 0); /* Clear all flags: New grace period. */
1753

1754 1755 1756 1757 1758
	if (WARN_ON_ONCE(rcu_gp_in_progress(rsp))) {
		/*
		 * Grace period already in progress, don't start another.
		 * Not supposed to be able to happen.
		 */
1759 1760 1761 1762 1763
		raw_spin_unlock_irq(&rnp->lock);
		return 0;
	}

	/* Advance to a new grace period and initialize state. */
1764
	record_gp_stall_check_time(rsp);
1765 1766
	/* Record GP times before starting GP, hence smp_store_release(). */
	smp_store_release(&rsp->gpnum, rsp->gpnum + 1);
1767
	trace_rcu_grace_period(rsp->name, rsp->gpnum, TPS("start"));
1768 1769
	raw_spin_unlock_irq(&rnp->lock);

1770 1771 1772 1773 1774 1775 1776 1777 1778 1779 1780 1781 1782 1783 1784 1785 1786 1787 1788 1789 1790 1791 1792 1793 1794 1795 1796 1797 1798 1799 1800 1801 1802 1803 1804 1805 1806 1807 1808 1809 1810 1811 1812 1813 1814 1815 1816 1817
	/*
	 * Apply per-leaf buffered online and offline operations to the
	 * rcu_node tree.  Note that this new grace period need not wait
	 * for subsequent online CPUs, and that quiescent-state forcing
	 * will handle subsequent offline CPUs.
	 */
	rcu_for_each_leaf_node(rsp, rnp) {
		raw_spin_lock_irq(&rnp->lock);
		smp_mb__after_unlock_lock();
		if (rnp->qsmaskinit == rnp->qsmaskinitnext &&
		    !rnp->wait_blkd_tasks) {
			/* Nothing to do on this leaf rcu_node structure. */
			raw_spin_unlock_irq(&rnp->lock);
			continue;
		}

		/* Record old state, apply changes to ->qsmaskinit field. */
		oldmask = rnp->qsmaskinit;
		rnp->qsmaskinit = rnp->qsmaskinitnext;

		/* If zero-ness of ->qsmaskinit changed, propagate up tree. */
		if (!oldmask != !rnp->qsmaskinit) {
			if (!oldmask) /* First online CPU for this rcu_node. */
				rcu_init_new_rnp(rnp);
			else if (rcu_preempt_has_tasks(rnp)) /* blocked tasks */
				rnp->wait_blkd_tasks = true;
			else /* Last offline CPU and can propagate. */
				rcu_cleanup_dead_rnp(rnp);
		}

		/*
		 * If all waited-on tasks from prior grace period are
		 * done, and if all this rcu_node structure's CPUs are
		 * still offline, propagate up the rcu_node tree and
		 * clear ->wait_blkd_tasks.  Otherwise, if one of this
		 * rcu_node structure's CPUs has since come back online,
		 * simply clear ->wait_blkd_tasks (but rcu_cleanup_dead_rnp()
		 * checks for this, so just call it unconditionally).
		 */
		if (rnp->wait_blkd_tasks &&
		    (!rcu_preempt_has_tasks(rnp) ||
		     rnp->qsmaskinit)) {
			rnp->wait_blkd_tasks = false;
			rcu_cleanup_dead_rnp(rnp);
		}

		raw_spin_unlock_irq(&rnp->lock);
	}
1818 1819 1820 1821 1822 1823 1824 1825 1826 1827 1828 1829 1830 1831 1832

	/*
	 * Set the quiescent-state-needed bits in all the rcu_node
	 * structures for all currently online CPUs in breadth-first order,
	 * starting from the root rcu_node structure, relying on the layout
	 * of the tree within the rsp->node[] array.  Note that other CPUs
	 * will access only the leaves of the hierarchy, thus seeing that no
	 * grace period is in progress, at least until the corresponding
	 * leaf node has been initialized.  In addition, we have excluded
	 * CPU-hotplug operations.
	 *
	 * The grace period cannot complete until the initialization
	 * process finishes, because this kthread handles both.
	 */
	rcu_for_each_node_breadth_first(rsp, rnp) {
1833
		raw_spin_lock_irq(&rnp->lock);
1834
		smp_mb__after_unlock_lock();
1835
		rdp = this_cpu_ptr(rsp->rda);
1836 1837
		rcu_preempt_check_blocked_tasks(rnp);
		rnp->qsmask = rnp->qsmaskinit;
1838
		WRITE_ONCE(rnp->gpnum, rsp->gpnum);
1839
		if (WARN_ON_ONCE(rnp->completed != rsp->completed))
1840
			WRITE_ONCE(rnp->completed, rsp->completed);
1841
		if (rnp == rdp->mynode)
1842
			(void)__note_gp_changes(rsp, rnp, rdp);
1843 1844 1845 1846 1847
		rcu_preempt_boost_start_gp(rnp);
		trace_rcu_grace_period_init(rsp->name, rnp->gpnum,
					    rnp->level, rnp->grplo,
					    rnp->grphi, rnp->qsmask);
		raw_spin_unlock_irq(&rnp->lock);
1848
		cond_resched_rcu_qs();
1849
		WRITE_ONCE(rsp->gp_activity, jiffies);
1850 1851
		if (gp_init_delay > 0 &&
		    !(rsp->gpnum % (rcu_num_nodes * PER_RCU_NODE_PERIOD)))
1852
			schedule_timeout_uninterruptible(gp_init_delay);
1853
	}
1854

1855 1856
	return 1;
}
1857

1858 1859 1860
/*
 * Do one round of quiescent-state forcing.
 */
1861
static int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in)
1862 1863
{
	int fqs_state = fqs_state_in;
1864 1865
	bool isidle = false;
	unsigned long maxj;
1866 1867
	struct rcu_node *rnp = rcu_get_root(rsp);

1868
	WRITE_ONCE(rsp->gp_activity, jiffies);
1869 1870 1871
	rsp->n_force_qs++;
	if (fqs_state == RCU_SAVE_DYNTICK) {
		/* Collect dyntick-idle snapshots. */
1872
		if (is_sysidle_rcu_state(rsp)) {
1873
			isidle = true;
1874 1875
			maxj = jiffies - ULONG_MAX / 4;
		}
1876 1877
		force_qs_rnp(rsp, dyntick_save_progress_counter,
			     &isidle, &maxj);
1878
		rcu_sysidle_report_gp(rsp, isidle, maxj);
1879 1880 1881
		fqs_state = RCU_FORCE_QS;
	} else {
		/* Handle dyntick-idle and offline CPUs. */
1882
		isidle = true;
1883
		force_qs_rnp(rsp, rcu_implicit_dynticks_qs, &isidle, &maxj);
1884 1885
	}
	/* Clear flag to prevent immediate re-entry. */
1886
	if (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
1887
		raw_spin_lock_irq(&rnp->lock);
1888
		smp_mb__after_unlock_lock();
1889 1890
		WRITE_ONCE(rsp->gp_flags,
			   READ_ONCE(rsp->gp_flags) & ~RCU_GP_FLAG_FQS);
1891 1892 1893 1894 1895
		raw_spin_unlock_irq(&rnp->lock);
	}
	return fqs_state;
}

1896 1897 1898
/*
 * Clean up after the old grace period.
 */
1899
static void rcu_gp_cleanup(struct rcu_state *rsp)
1900 1901
{
	unsigned long gp_duration;
1902
	bool needgp = false;
1903
	int nocb = 0;
1904 1905
	struct rcu_data *rdp;
	struct rcu_node *rnp = rcu_get_root(rsp);
1906

1907
	WRITE_ONCE(rsp->gp_activity, jiffies);
1908
	raw_spin_lock_irq(&rnp->lock);
1909
	smp_mb__after_unlock_lock();
1910 1911 1912
	gp_duration = jiffies - rsp->gp_start;
	if (gp_duration > rsp->gp_max)
		rsp->gp_max = gp_duration;
1913

1914 1915 1916 1917 1918 1919 1920 1921
	/*
	 * We know the grace period is complete, but to everyone else
	 * it appears to still be ongoing.  But it is also the case
	 * that to everyone else it looks like there is nothing that
	 * they can do to advance the grace period.  It is therefore
	 * safe for us to drop the lock in order to mark the grace
	 * period as completed in all of the rcu_node structures.
	 */
1922
	raw_spin_unlock_irq(&rnp->lock);
1923

1924 1925 1926 1927 1928 1929 1930 1931 1932 1933
	/*
	 * Propagate new ->completed value to rcu_node structures so
	 * that other CPUs don't have to wait until the start of the next
	 * grace period to process their callbacks.  This also avoids
	 * some nasty RCU grace-period initialization races by forcing
	 * the end of the current grace period to be completely recorded in
	 * all of the rcu_node structures before the beginning of the next
	 * grace period is recorded in any of the rcu_node structures.
	 */
	rcu_for_each_node_breadth_first(rsp, rnp) {
1934
		raw_spin_lock_irq(&rnp->lock);
1935
		smp_mb__after_unlock_lock();
1936 1937
		WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
		WARN_ON_ONCE(rnp->qsmask);
1938
		WRITE_ONCE(rnp->completed, rsp->gpnum);
1939 1940
		rdp = this_cpu_ptr(rsp->rda);
		if (rnp == rdp->mynode)
1941
			needgp = __note_gp_changes(rsp, rnp, rdp) || needgp;
1942
		/* smp_mb() provided by prior unlock-lock pair. */
1943
		nocb += rcu_future_gp_cleanup(rsp, rnp);
1944
		raw_spin_unlock_irq(&rnp->lock);
1945
		cond_resched_rcu_qs();
1946
		WRITE_ONCE(rsp->gp_activity, jiffies);
1947
	}
1948 1949
	rnp = rcu_get_root(rsp);
	raw_spin_lock_irq(&rnp->lock);
1950
	smp_mb__after_unlock_lock(); /* Order GP before ->completed update. */
1951
	rcu_nocb_gp_set(rnp, nocb);
1952

1953
	/* Declare grace period done. */
1954
	WRITE_ONCE(rsp->completed, rsp->gpnum);
1955
	trace_rcu_grace_period(rsp->name, rsp->completed, TPS("end"));
1956
	rsp->fqs_state = RCU_GP_IDLE;
1957
	rdp = this_cpu_ptr(rsp->rda);
1958 1959 1960
	/* Advance CBs to reduce false positives below. */
	needgp = rcu_advance_cbs(rsp, rnp, rdp) || needgp;
	if (needgp || cpu_needs_another_gp(rsp, rdp)) {
1961
		WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT);
1962
		trace_rcu_grace_period(rsp->name,
1963
				       READ_ONCE(rsp->gpnum),
1964 1965
				       TPS("newreq"));
	}
1966 1967 1968 1969 1970 1971 1972 1973
	raw_spin_unlock_irq(&rnp->lock);
}

/*
 * Body of kthread that handles grace periods.
 */
static int __noreturn rcu_gp_kthread(void *arg)
{
1974
	int fqs_state;
1975
	int gf;
1976
	unsigned long j;
1977
	int ret;
1978 1979 1980
	struct rcu_state *rsp = arg;
	struct rcu_node *rnp = rcu_get_root(rsp);

1981
	rcu_bind_gp_kthread();
1982 1983 1984 1985
	for (;;) {

		/* Handle grace-period start. */
		for (;;) {
1986
			trace_rcu_grace_period(rsp->name,
1987
					       READ_ONCE(rsp->gpnum),
1988
					       TPS("reqwait"));
1989
			rsp->gp_state = RCU_GP_WAIT_GPS;
1990
			wait_event_interruptible(rsp->gp_wq,
1991
						 READ_ONCE(rsp->gp_flags) &
1992
						 RCU_GP_FLAG_INIT);
1993
			/* Locking provides needed memory barrier. */
1994
			if (rcu_gp_init(rsp))
1995
				break;
1996
			cond_resched_rcu_qs();
1997
			WRITE_ONCE(rsp->gp_activity, jiffies);
1998
			WARN_ON(signal_pending(current));
1999
			trace_rcu_grace_period(rsp->name,
2000
					       READ_ONCE(rsp->gpnum),
2001
					       TPS("reqwaitsig"));
2002
		}
2003

2004 2005
		/* Handle quiescent-state forcing. */
		fqs_state = RCU_SAVE_DYNTICK;
2006 2007 2008 2009 2010
		j = jiffies_till_first_fqs;
		if (j > HZ) {
			j = HZ;
			jiffies_till_first_fqs = HZ;
		}
2011
		ret = 0;
2012
		for (;;) {
2013 2014
			if (!ret)
				rsp->jiffies_force_qs = jiffies + j;
2015
			trace_rcu_grace_period(rsp->name,
2016
					       READ_ONCE(rsp->gpnum),
2017
					       TPS("fqswait"));
2018
			rsp->gp_state = RCU_GP_WAIT_FQS;
2019
			ret = wait_event_interruptible_timeout(rsp->gp_wq,
2020
					((gf = READ_ONCE(rsp->gp_flags)) &
2021
					 RCU_GP_FLAG_FQS) ||
2022
					(!READ_ONCE(rnp->qsmask) &&
2023
					 !rcu_preempt_blocked_readers_cgp(rnp)),
2024
					j);
2025
			/* Locking provides needed memory barriers. */
2026
			/* If grace period done, leave loop. */
2027
			if (!READ_ONCE(rnp->qsmask) &&
2028
			    !rcu_preempt_blocked_readers_cgp(rnp))
2029
				break;
2030
			/* If time for quiescent-state forcing, do it. */
2031 2032
			if (ULONG_CMP_GE(jiffies, rsp->jiffies_force_qs) ||
			    (gf & RCU_GP_FLAG_FQS)) {
2033
				trace_rcu_grace_period(rsp->name,
2034
						       READ_ONCE(rsp->gpnum),
2035
						       TPS("fqsstart"));
2036
				fqs_state = rcu_gp_fqs(rsp, fqs_state);
2037
				trace_rcu_grace_period(rsp->name,
2038
						       READ_ONCE(rsp->gpnum),
2039
						       TPS("fqsend"));
2040
				cond_resched_rcu_qs();
2041
				WRITE_ONCE(rsp->gp_activity, jiffies);
2042 2043
			} else {
				/* Deal with stray signal. */
2044
				cond_resched_rcu_qs();
2045
				WRITE_ONCE(rsp->gp_activity, jiffies);
2046
				WARN_ON(signal_pending(current));
2047
				trace_rcu_grace_period(rsp->name,
2048
						       READ_ONCE(rsp->gpnum),
2049
						       TPS("fqswaitsig"));
2050
			}
2051 2052 2053 2054 2055 2056 2057 2058
			j = jiffies_till_next_fqs;
			if (j > HZ) {
				j = HZ;
				jiffies_till_next_fqs = HZ;
			} else if (j < 1) {
				j = 1;
				jiffies_till_next_fqs = 1;
			}
2059
		}
2060 2061 2062

		/* Handle grace-period end. */
		rcu_gp_cleanup(rsp);
2063 2064 2065
	}
}

2066 2067 2068
/*
 * Start a new RCU grace period if warranted, re-initializing the hierarchy
 * in preparation for detecting the next grace period.  The caller must hold
2069
 * the root node's ->lock and hard irqs must be disabled.
2070 2071 2072 2073
 *
 * Note that it is legal for a dying CPU (which is marked as offline) to
 * invoke this function.  This can happen when the dying CPU reports its
 * quiescent state.
2074 2075
 *
 * Returns true if the grace-period kthread must be awakened.
2076
 */
2077
static bool
2078 2079
rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
		      struct rcu_data *rdp)
2080
{
2081
	if (!rsp->gp_kthread || !cpu_needs_another_gp(rsp, rdp)) {
2082
		/*
2083
		 * Either we have not yet spawned the grace-period
2084 2085
		 * task, this CPU does not need another grace period,
		 * or a grace period is already in progress.
2086
		 * Either way, don't start a new grace period.
2087
		 */
2088
		return false;
2089
	}
2090 2091
	WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT);
	trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gpnum),
2092
			       TPS("newreq"));
2093

2094 2095
	/*
	 * We can't do wakeups while holding the rnp->lock, as that
2096
	 * could cause possible deadlocks with the rq->lock. Defer
2097
	 * the wakeup to our caller.
2098
	 */
2099
	return true;
2100 2101
}

2102 2103 2104 2105 2106 2107
/*
 * Similar to rcu_start_gp_advanced(), but also advance the calling CPU's
 * callbacks.  Note that rcu_start_gp_advanced() cannot do this because it
 * is invoked indirectly from rcu_advance_cbs(), which would result in
 * endless recursion -- or would do so if it wasn't for the self-deadlock
 * that is encountered beforehand.
2108 2109
 *
 * Returns true if the grace-period kthread needs to be awakened.
2110
 */
2111
static bool rcu_start_gp(struct rcu_state *rsp)
2112 2113 2114
{
	struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
	struct rcu_node *rnp = rcu_get_root(rsp);
2115
	bool ret = false;
2116 2117 2118 2119 2120 2121 2122 2123 2124

	/*
	 * If there is no grace period in progress right now, any
	 * callbacks we have up to this point will be satisfied by the
	 * next grace period.  Also, advancing the callbacks reduces the
	 * probability of false positives from cpu_needs_another_gp()
	 * resulting in pointless grace periods.  So, advance callbacks
	 * then start the grace period!
	 */
2125 2126 2127
	ret = rcu_advance_cbs(rsp, rnp, rdp) || ret;
	ret = rcu_start_gp_advanced(rsp, rnp, rdp) || ret;
	return ret;
2128 2129
}

2130
/*
P
Paul E. McKenney 已提交
2131 2132 2133
 * Report a full set of quiescent states to the specified rcu_state
 * data structure.  This involves cleaning up after the prior grace
 * period and letting rcu_start_gp() start up the next grace period
2134 2135
 * if one is needed.  Note that the caller must hold rnp->lock, which
 * is released before return.
2136
 */
P
Paul E. McKenney 已提交
2137
static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
2138
	__releases(rcu_get_root(rsp)->lock)
2139
{
2140
	WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
2141
	raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags);
2142
	rcu_gp_kthread_wake(rsp);
2143 2144
}

2145
/*
P
Paul E. McKenney 已提交
2146 2147 2148
 * Similar to rcu_report_qs_rdp(), for which it is a helper function.
 * Allows quiescent states for a group of CPUs to be reported at one go
 * to the specified rcu_node structure, though all the CPUs in the group
2149 2150 2151 2152 2153
 * must be represented by the same rcu_node structure (which need not be a
 * leaf rcu_node structure, though it often will be).  The gps parameter
 * is the grace-period snapshot, which means that the quiescent states
 * are valid only if rnp->gpnum is equal to gps.  That structure's lock
 * must be held upon entry, and it is released before return.
2154 2155
 */
static void
P
Paul E. McKenney 已提交
2156
rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
2157
		  struct rcu_node *rnp, unsigned long gps, unsigned long flags)
2158 2159
	__releases(rnp->lock)
{
2160
	unsigned long oldmask = 0;
2161 2162
	struct rcu_node *rnp_c;

2163 2164
	/* Walk up the rcu_node hierarchy. */
	for (;;) {
2165
		if (!(rnp->qsmask & mask) || rnp->gpnum != gps) {
2166

2167 2168 2169 2170
			/*
			 * Our bit has already been cleared, or the
			 * relevant grace period is already over, so done.
			 */
P
Paul E. McKenney 已提交
2171
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
2172 2173
			return;
		}
2174
		WARN_ON_ONCE(oldmask); /* Any child must be all zeroed! */
2175
		rnp->qsmask &= ~mask;
2176 2177 2178 2179
		trace_rcu_quiescent_state_report(rsp->name, rnp->gpnum,
						 mask, rnp->qsmask, rnp->level,
						 rnp->grplo, rnp->grphi,
						 !!rnp->gp_tasks);
2180
		if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
2181 2182

			/* Other bits still set at this level, so done. */
P
Paul E. McKenney 已提交
2183
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
2184 2185 2186 2187 2188 2189 2190 2191 2192
			return;
		}
		mask = rnp->grpmask;
		if (rnp->parent == NULL) {

			/* No more levels.  Exit loop holding root lock. */

			break;
		}
P
Paul E. McKenney 已提交
2193
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
2194
		rnp_c = rnp;
2195
		rnp = rnp->parent;
P
Paul E. McKenney 已提交
2196
		raw_spin_lock_irqsave(&rnp->lock, flags);
2197
		smp_mb__after_unlock_lock();
2198
		oldmask = rnp_c->qsmask;
2199 2200 2201 2202
	}

	/*
	 * Get here if we are the last CPU to pass through a quiescent
P
Paul E. McKenney 已提交
2203
	 * state for this grace period.  Invoke rcu_report_qs_rsp()
2204
	 * to clean up and start the next grace period if one is needed.
2205
	 */
P
Paul E. McKenney 已提交
2206
	rcu_report_qs_rsp(rsp, flags); /* releases rnp->lock. */
2207 2208
}

2209 2210 2211 2212 2213 2214 2215
/*
 * Record a quiescent state for all tasks that were previously queued
 * on the specified rcu_node structure and that were blocking the current
 * RCU grace period.  The caller must hold the specified rnp->lock with
 * irqs disabled, and this lock is released upon return, but irqs remain
 * disabled.
 */
2216
static void rcu_report_unblock_qs_rnp(struct rcu_state *rsp,
2217 2218 2219
				      struct rcu_node *rnp, unsigned long flags)
	__releases(rnp->lock)
{
2220
	unsigned long gps;
2221 2222 2223
	unsigned long mask;
	struct rcu_node *rnp_p;

2224 2225
	if (rcu_state_p == &rcu_sched_state || rsp != rcu_state_p ||
	    rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
2226 2227 2228 2229 2230 2231 2232
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
		return;  /* Still need more quiescent states! */
	}

	rnp_p = rnp->parent;
	if (rnp_p == NULL) {
		/*
2233 2234
		 * Only one rcu_node structure in the tree, so don't
		 * try to report up to its nonexistent parent!
2235 2236 2237 2238 2239
		 */
		rcu_report_qs_rsp(rsp, flags);
		return;
	}

2240 2241
	/* Report up the rest of the hierarchy, tracking current ->gpnum. */
	gps = rnp->gpnum;
2242 2243 2244 2245
	mask = rnp->grpmask;
	raw_spin_unlock(&rnp->lock);	/* irqs remain disabled. */
	raw_spin_lock(&rnp_p->lock);	/* irqs already disabled. */
	smp_mb__after_unlock_lock();
2246
	rcu_report_qs_rnp(mask, rsp, rnp_p, gps, flags);
2247 2248
}

2249
/*
P
Paul E. McKenney 已提交
2250 2251 2252 2253 2254 2255 2256
 * Record a quiescent state for the specified CPU to that CPU's rcu_data
 * structure.  This must be either called from the specified CPU, or
 * called when the specified CPU is known to be offline (and when it is
 * also known that no other CPU is concurrently trying to help the offline
 * CPU).  The lastcomp argument is used to make sure we are still in the
 * grace period of interest.  We don't want to end the current grace period
 * based on quiescent states detected in an earlier grace period!
2257 2258
 */
static void
2259
rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp)
2260 2261 2262
{
	unsigned long flags;
	unsigned long mask;
2263
	bool needwake;
2264 2265 2266
	struct rcu_node *rnp;

	rnp = rdp->mynode;
P
Paul E. McKenney 已提交
2267
	raw_spin_lock_irqsave(&rnp->lock, flags);
2268
	smp_mb__after_unlock_lock();
2269 2270 2271 2272
	if ((rdp->passed_quiesce == 0 &&
	     rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_qs_ctr)) ||
	    rdp->gpnum != rnp->gpnum || rnp->completed == rnp->gpnum ||
	    rdp->gpwrap) {
2273 2274

		/*
2275 2276 2277 2278
		 * The grace period in which this quiescent state was
		 * recorded has ended, so don't report it upwards.
		 * We will instead need a new quiescent state that lies
		 * within the current grace period.
2279
		 */
2280
		rdp->passed_quiesce = 0;	/* need qs for new gp. */
2281
		rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_qs_ctr);
P
Paul E. McKenney 已提交
2282
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
2283 2284 2285 2286
		return;
	}
	mask = rdp->grpmask;
	if ((rnp->qsmask & mask) == 0) {
P
Paul E. McKenney 已提交
2287
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
2288 2289 2290 2291 2292 2293 2294
	} else {
		rdp->qs_pending = 0;

		/*
		 * This GP can't end until cpu checks in, so all of our
		 * callbacks can be processed during the next GP.
		 */
2295
		needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
2296

2297 2298
		rcu_report_qs_rnp(mask, rsp, rnp, rnp->gpnum, flags);
		/* ^^^ Released rnp->lock */
2299 2300
		if (needwake)
			rcu_gp_kthread_wake(rsp);
2301 2302 2303 2304 2305 2306 2307 2308 2309 2310 2311 2312
	}
}

/*
 * Check to see if there is a new grace period of which this CPU
 * is not yet aware, and if so, set up local rcu_data state for it.
 * Otherwise, see if this CPU has just passed through its first
 * quiescent state for this grace period, and record that fact if so.
 */
static void
rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
{
2313 2314
	/* Check for grace-period ends and beginnings. */
	note_gp_changes(rsp, rdp);
2315 2316 2317 2318 2319 2320 2321 2322 2323 2324 2325 2326

	/*
	 * Does this CPU still need to do its part for current grace period?
	 * If no, return and let the other CPUs do their part as well.
	 */
	if (!rdp->qs_pending)
		return;

	/*
	 * Was there a quiescent state since the beginning of the grace
	 * period? If no, then exit and wait for the next call.
	 */
2327 2328
	if (!rdp->passed_quiesce &&
	    rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_qs_ctr))
2329 2330
		return;

P
Paul E. McKenney 已提交
2331 2332 2333 2334
	/*
	 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
	 * judge of that).
	 */
2335
	rcu_report_qs_rdp(rdp->cpu, rsp, rdp);
2336 2337 2338 2339
}

#ifdef CONFIG_HOTPLUG_CPU

2340
/*
2341 2342
 * Send the specified CPU's RCU callbacks to the orphanage.  The
 * specified CPU must be offline, and the caller must hold the
2343
 * ->orphan_lock.
2344
 */
2345 2346 2347
static void
rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
			  struct rcu_node *rnp, struct rcu_data *rdp)
2348
{
P
Paul E. McKenney 已提交
2349
	/* No-CBs CPUs do not have orphanable callbacks. */
2350
	if (rcu_is_nocb_cpu(rdp->cpu))
P
Paul E. McKenney 已提交
2351 2352
		return;

2353 2354
	/*
	 * Orphan the callbacks.  First adjust the counts.  This is safe
2355 2356
	 * because _rcu_barrier() excludes CPU-hotplug operations, so it
	 * cannot be running now.  Thus no memory barrier is required.
2357
	 */
2358
	if (rdp->nxtlist != NULL) {
2359 2360 2361
		rsp->qlen_lazy += rdp->qlen_lazy;
		rsp->qlen += rdp->qlen;
		rdp->n_cbs_orphaned += rdp->qlen;
2362
		rdp->qlen_lazy = 0;
2363
		WRITE_ONCE(rdp->qlen, 0);
2364 2365 2366
	}

	/*
2367 2368 2369 2370 2371 2372 2373
	 * Next, move those callbacks still needing a grace period to
	 * the orphanage, where some other CPU will pick them up.
	 * Some of the callbacks might have gone partway through a grace
	 * period, but that is too bad.  They get to start over because we
	 * cannot assume that grace periods are synchronized across CPUs.
	 * We don't bother updating the ->nxttail[] array yet, instead
	 * we just reset the whole thing later on.
2374
	 */
2375 2376 2377 2378
	if (*rdp->nxttail[RCU_DONE_TAIL] != NULL) {
		*rsp->orphan_nxttail = *rdp->nxttail[RCU_DONE_TAIL];
		rsp->orphan_nxttail = rdp->nxttail[RCU_NEXT_TAIL];
		*rdp->nxttail[RCU_DONE_TAIL] = NULL;
2379 2380 2381
	}

	/*
2382 2383 2384
	 * Then move the ready-to-invoke callbacks to the orphanage,
	 * where some other CPU will pick them up.  These will not be
	 * required to pass though another grace period: They are done.
2385
	 */
2386
	if (rdp->nxtlist != NULL) {
2387 2388
		*rsp->orphan_donetail = rdp->nxtlist;
		rsp->orphan_donetail = rdp->nxttail[RCU_DONE_TAIL];
2389
	}
2390

2391 2392 2393 2394
	/*
	 * Finally, initialize the rcu_data structure's list to empty and
	 * disallow further callbacks on this CPU.
	 */
2395
	init_callback_list(rdp);
2396
	rdp->nxttail[RCU_NEXT_TAIL] = NULL;
2397 2398 2399 2400
}

/*
 * Adopt the RCU callbacks from the specified rcu_state structure's
2401
 * orphanage.  The caller must hold the ->orphan_lock.
2402
 */
2403
static void rcu_adopt_orphan_cbs(struct rcu_state *rsp, unsigned long flags)
2404 2405
{
	int i;
2406
	struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
2407

P
Paul E. McKenney 已提交
2408
	/* No-CBs CPUs are handled specially. */
2409
	if (rcu_nocb_adopt_orphan_cbs(rsp, rdp, flags))
P
Paul E. McKenney 已提交
2410 2411
		return;

2412 2413 2414 2415
	/* Do the accounting first. */
	rdp->qlen_lazy += rsp->qlen_lazy;
	rdp->qlen += rsp->qlen;
	rdp->n_cbs_adopted += rsp->qlen;
2416 2417
	if (rsp->qlen_lazy != rsp->qlen)
		rcu_idle_count_callbacks_posted();
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
	rsp->qlen_lazy = 0;
	rsp->qlen = 0;

	/*
	 * We do not need a memory barrier here because the only way we
	 * can get here if there is an rcu_barrier() in flight is if
	 * we are the task doing the rcu_barrier().
	 */

	/* First adopt the ready-to-invoke callbacks. */
	if (rsp->orphan_donelist != NULL) {
		*rsp->orphan_donetail = *rdp->nxttail[RCU_DONE_TAIL];
		*rdp->nxttail[RCU_DONE_TAIL] = rsp->orphan_donelist;
		for (i = RCU_NEXT_SIZE - 1; i >= RCU_DONE_TAIL; i--)
			if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
				rdp->nxttail[i] = rsp->orphan_donetail;
		rsp->orphan_donelist = NULL;
		rsp->orphan_donetail = &rsp->orphan_donelist;
	}

	/* And then adopt the callbacks that still need a grace period. */
	if (rsp->orphan_nxtlist != NULL) {
		*rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxtlist;
		rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxttail;
		rsp->orphan_nxtlist = NULL;
		rsp->orphan_nxttail = &rsp->orphan_nxtlist;
	}
}

/*
 * Trace the fact that this CPU is going offline.
 */
static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
{
	RCU_TRACE(unsigned long mask);
	RCU_TRACE(struct rcu_data *rdp = this_cpu_ptr(rsp->rda));
	RCU_TRACE(struct rcu_node *rnp = rdp->mynode);

	RCU_TRACE(mask = rdp->grpmask);
2457 2458
	trace_rcu_grace_period(rsp->name,
			       rnp->gpnum + 1 - !!(rnp->qsmask & mask),
2459
			       TPS("cpuofl"));
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
/*
 * All CPUs for the specified rcu_node structure have gone offline,
 * and all tasks that were preempted within an RCU read-side critical
 * section while running on one of those CPUs have since exited their RCU
 * read-side critical section.  Some other CPU is reporting this fact with
 * the specified rcu_node structure's ->lock held and interrupts disabled.
 * This function therefore goes up the tree of rcu_node structures,
 * clearing the corresponding bits in the ->qsmaskinit fields.  Note that
 * the leaf rcu_node structure's ->qsmaskinit field has already been
 * updated
 *
 * This function does check that the specified rcu_node structure has
 * all CPUs offline and no blocked tasks, so it is OK to invoke it
 * prematurely.  That said, invoking it after the fact will cost you
 * a needless lock acquisition.  So once it has done its work, don't
 * invoke it again.
 */
static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf)
{
	long mask;
	struct rcu_node *rnp = rnp_leaf;

	if (rnp->qsmaskinit || rcu_preempt_has_tasks(rnp))
		return;
	for (;;) {
		mask = rnp->grpmask;
		rnp = rnp->parent;
		if (!rnp)
			break;
		raw_spin_lock(&rnp->lock); /* irqs already disabled. */
		smp_mb__after_unlock_lock(); /* GP memory ordering. */
		rnp->qsmaskinit &= ~mask;
2494
		rnp->qsmask &= ~mask;
2495 2496 2497 2498 2499 2500 2501 2502
		if (rnp->qsmaskinit) {
			raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
			return;
		}
		raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
	}
}

2503 2504 2505 2506 2507 2508 2509 2510 2511 2512 2513 2514 2515 2516 2517 2518 2519 2520 2521 2522
/*
 * The CPU is exiting the idle loop into the arch_cpu_idle_dead()
 * function.  We now remove it from the rcu_node tree's ->qsmaskinit
 * bit masks.
 */
static void rcu_cleanup_dying_idle_cpu(int cpu, struct rcu_state *rsp)
{
	unsigned long flags;
	unsigned long mask;
	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
	struct rcu_node *rnp = rdp->mynode;  /* Outgoing CPU's rdp & rnp. */

	/* Remove outgoing CPU from mask in the leaf rcu_node structure. */
	mask = rdp->grpmask;
	raw_spin_lock_irqsave(&rnp->lock, flags);
	smp_mb__after_unlock_lock();	/* Enforce GP memory-order guarantee. */
	rnp->qsmaskinitnext &= ~mask;
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
}

2523
/*
2524
 * The CPU has been completely removed, and some other CPU is reporting
2525 2526
 * this fact from process context.  Do the remainder of the cleanup,
 * including orphaning the outgoing CPU's RCU callbacks, and also
2527 2528
 * adopting them.  There can only be one CPU hotplug operation at a time,
 * so no other CPU can be attempting to update rcu_cpu_kthread_task.
2529
 */
2530
static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
2531
{
2532
	unsigned long flags;
2533
	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
2534
	struct rcu_node *rnp = rdp->mynode;  /* Outgoing CPU's rdp & rnp. */
2535

2536
	/* Adjust any no-longer-needed kthreads. */
T
Thomas Gleixner 已提交
2537
	rcu_boost_kthread_setaffinity(rnp, -1);
2538

2539
	/* Orphan the dead CPU's callbacks, and adopt them if appropriate. */
2540
	raw_spin_lock_irqsave(&rsp->orphan_lock, flags);
2541
	rcu_send_cbs_to_orphanage(cpu, rsp, rnp, rdp);
2542
	rcu_adopt_orphan_cbs(rsp, flags);
2543
	raw_spin_unlock_irqrestore(&rsp->orphan_lock, flags);
2544

2545 2546 2547
	WARN_ONCE(rdp->qlen != 0 || rdp->nxtlist != NULL,
		  "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, nxtlist=%p\n",
		  cpu, rdp->qlen, rdp->nxtlist);
2548 2549 2550 2551
}

#else /* #ifdef CONFIG_HOTPLUG_CPU */

2552
static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
2553 2554 2555
{
}

2556 2557 2558 2559
static void __maybe_unused rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf)
{
}

2560 2561 2562 2563
static void rcu_cleanup_dying_idle_cpu(int cpu, struct rcu_state *rsp)
{
}

2564
static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
2565 2566 2567 2568 2569 2570 2571 2572 2573
{
}

#endif /* #else #ifdef CONFIG_HOTPLUG_CPU */

/*
 * Invoke any RCU callbacks that have made it to the end of their grace
 * period.  Thottle as specified by rdp->blimit.
 */
2574
static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
2575 2576 2577
{
	unsigned long flags;
	struct rcu_head *next, *list, **tail;
E
Eric Dumazet 已提交
2578 2579
	long bl, count, count_lazy;
	int i;
2580

2581
	/* If no callbacks are ready, just return. */
2582
	if (!cpu_has_callbacks_ready_to_invoke(rdp)) {
2583
		trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, 0);
2584
		trace_rcu_batch_end(rsp->name, 0, !!READ_ONCE(rdp->nxtlist),
2585 2586
				    need_resched(), is_idle_task(current),
				    rcu_is_callbacks_kthread());
2587
		return;
2588
	}
2589 2590 2591 2592 2593 2594

	/*
	 * Extract the list of ready callbacks, disabling to prevent
	 * races with call_rcu() from interrupt handlers.
	 */
	local_irq_save(flags);
2595
	WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
2596
	bl = rdp->blimit;
2597
	trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, bl);
2598 2599 2600 2601
	list = rdp->nxtlist;
	rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
	*rdp->nxttail[RCU_DONE_TAIL] = NULL;
	tail = rdp->nxttail[RCU_DONE_TAIL];
2602 2603 2604
	for (i = RCU_NEXT_SIZE - 1; i >= 0; i--)
		if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
			rdp->nxttail[i] = &rdp->nxtlist;
2605 2606 2607
	local_irq_restore(flags);

	/* Invoke callbacks. */
2608
	count = count_lazy = 0;
2609 2610 2611
	while (list) {
		next = list->next;
		prefetch(next);
2612
		debug_rcu_head_unqueue(list);
2613 2614
		if (__rcu_reclaim(rsp->name, list))
			count_lazy++;
2615
		list = next;
2616 2617 2618 2619
		/* Stop only if limit reached and CPU has something to do. */
		if (++count >= bl &&
		    (need_resched() ||
		     (!is_idle_task(current) && !rcu_is_callbacks_kthread())))
2620 2621 2622 2623
			break;
	}

	local_irq_save(flags);
2624 2625 2626
	trace_rcu_batch_end(rsp->name, count, !!list, need_resched(),
			    is_idle_task(current),
			    rcu_is_callbacks_kthread());
2627 2628 2629 2630 2631

	/* Update count, and requeue any remaining callbacks. */
	if (list != NULL) {
		*tail = rdp->nxtlist;
		rdp->nxtlist = list;
2632 2633 2634
		for (i = 0; i < RCU_NEXT_SIZE; i++)
			if (&rdp->nxtlist == rdp->nxttail[i])
				rdp->nxttail[i] = tail;
2635 2636 2637
			else
				break;
	}
2638 2639
	smp_mb(); /* List handling before counting for rcu_barrier(). */
	rdp->qlen_lazy -= count_lazy;
2640
	WRITE_ONCE(rdp->qlen, rdp->qlen - count);
2641
	rdp->n_cbs_invoked += count;
2642 2643 2644 2645 2646

	/* Reinstate batch limit if we have worked down the excess. */
	if (rdp->blimit == LONG_MAX && rdp->qlen <= qlowmark)
		rdp->blimit = blimit;

2647 2648 2649 2650 2651 2652
	/* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
	if (rdp->qlen == 0 && rdp->qlen_last_fqs_check != 0) {
		rdp->qlen_last_fqs_check = 0;
		rdp->n_force_qs_snap = rsp->n_force_qs;
	} else if (rdp->qlen < rdp->qlen_last_fqs_check - qhimark)
		rdp->qlen_last_fqs_check = rdp->qlen;
2653
	WARN_ON_ONCE((rdp->nxtlist == NULL) != (rdp->qlen == 0));
2654

2655 2656
	local_irq_restore(flags);

2657
	/* Re-invoke RCU core processing if there are callbacks remaining. */
2658
	if (cpu_has_callbacks_ready_to_invoke(rdp))
2659
		invoke_rcu_core();
2660 2661 2662 2663 2664
}

/*
 * Check to see if this CPU is in a non-context-switch quiescent state
 * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
2665
 * Also schedule RCU core processing.
2666
 *
2667
 * This function must be called from hardirq context.  It is normally
2668 2669 2670
 * invoked from the scheduling-clock interrupt.  If rcu_pending returns
 * false, there is no point in invoking rcu_check_callbacks().
 */
2671
void rcu_check_callbacks(int user)
2672
{
2673
	trace_rcu_utilization(TPS("Start scheduler-tick"));
2674
	increment_cpu_stall_ticks();
2675
	if (user || rcu_is_cpu_rrupt_from_idle()) {
2676 2677 2678 2679 2680

		/*
		 * Get here if this CPU took its interrupt from user
		 * mode or from the idle loop, and if this is not a
		 * nested interrupt.  In this case, the CPU is in
2681
		 * a quiescent state, so note it.
2682 2683
		 *
		 * No memory barrier is required here because both
2684 2685 2686
		 * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
		 * variables that other CPUs neither access nor modify,
		 * at least not while the corresponding CPU is online.
2687 2688
		 */

2689 2690
		rcu_sched_qs();
		rcu_bh_qs();
2691 2692 2693 2694 2695 2696 2697

	} else if (!in_softirq()) {

		/*
		 * Get here if this CPU did not take its interrupt from
		 * softirq, in other words, if it is not interrupting
		 * a rcu_bh read-side critical section.  This is an _bh
2698
		 * critical section, so note it.
2699 2700
		 */

2701
		rcu_bh_qs();
2702
	}
2703
	rcu_preempt_check_callbacks();
2704
	if (rcu_pending())
2705
		invoke_rcu_core();
P
Paul E. McKenney 已提交
2706 2707
	if (user)
		rcu_note_voluntary_context_switch(current);
2708
	trace_rcu_utilization(TPS("End scheduler-tick"));
2709 2710 2711 2712 2713
}

/*
 * Scan the leaf rcu_node structures, processing dyntick state for any that
 * have not yet encountered a quiescent state, using the function specified.
2714 2715
 * Also initiate boosting for any threads blocked on the root rcu_node.
 *
2716
 * The caller must have suppressed start of new grace periods.
2717
 */
2718 2719 2720 2721
static void force_qs_rnp(struct rcu_state *rsp,
			 int (*f)(struct rcu_data *rsp, bool *isidle,
				  unsigned long *maxj),
			 bool *isidle, unsigned long *maxj)
2722 2723 2724 2725 2726
{
	unsigned long bit;
	int cpu;
	unsigned long flags;
	unsigned long mask;
2727
	struct rcu_node *rnp;
2728

2729
	rcu_for_each_leaf_node(rsp, rnp) {
2730
		cond_resched_rcu_qs();
2731
		mask = 0;
P
Paul E. McKenney 已提交
2732
		raw_spin_lock_irqsave(&rnp->lock, flags);
2733
		smp_mb__after_unlock_lock();
2734
		if (!rcu_gp_in_progress(rsp)) {
P
Paul E. McKenney 已提交
2735
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
2736
			return;
2737
		}
2738
		if (rnp->qsmask == 0) {
2739 2740 2741 2742 2743 2744 2745 2746 2747 2748 2749 2750 2751 2752 2753 2754 2755 2756 2757 2758 2759 2760 2761
			if (rcu_state_p == &rcu_sched_state ||
			    rsp != rcu_state_p ||
			    rcu_preempt_blocked_readers_cgp(rnp)) {
				/*
				 * No point in scanning bits because they
				 * are all zero.  But we might need to
				 * priority-boost blocked readers.
				 */
				rcu_initiate_boost(rnp, flags);
				/* rcu_initiate_boost() releases rnp->lock */
				continue;
			}
			if (rnp->parent &&
			    (rnp->parent->qsmask & rnp->grpmask)) {
				/*
				 * Race between grace-period
				 * initialization and task exiting RCU
				 * read-side critical section: Report.
				 */
				rcu_report_unblock_qs_rnp(rsp, rnp, flags);
				/* rcu_report_unblock_qs_rnp() rlses ->lock */
				continue;
			}
2762
		}
2763
		cpu = rnp->grplo;
2764
		bit = 1;
2765
		for (; cpu <= rnp->grphi; cpu++, bit <<= 1) {
2766
			if ((rnp->qsmask & bit) != 0) {
2767 2768
				if ((rnp->qsmaskinit & bit) == 0)
					*isidle = false; /* Pending hotplug. */
2769 2770 2771
				if (f(per_cpu_ptr(rsp->rda, cpu), isidle, maxj))
					mask |= bit;
			}
2772
		}
2773
		if (mask != 0) {
2774 2775
			/* Idle/offline CPUs, report (releases rnp->lock. */
			rcu_report_qs_rnp(mask, rsp, rnp, rnp->gpnum, flags);
2776 2777 2778
		} else {
			/* Nothing to do here, so just drop the lock. */
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
2779 2780 2781 2782 2783 2784 2785 2786
		}
	}
}

/*
 * Force quiescent states on reluctant CPUs, and also detect which
 * CPUs are in dyntick-idle mode.
 */
2787
static void force_quiescent_state(struct rcu_state *rsp)
2788 2789
{
	unsigned long flags;
2790 2791 2792 2793 2794
	bool ret;
	struct rcu_node *rnp;
	struct rcu_node *rnp_old = NULL;

	/* Funnel through hierarchy to reduce memory contention. */
2795
	rnp = __this_cpu_read(rsp->rda->mynode);
2796
	for (; rnp != NULL; rnp = rnp->parent) {
2797
		ret = (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) ||
2798 2799 2800 2801
		      !raw_spin_trylock(&rnp->fqslock);
		if (rnp_old != NULL)
			raw_spin_unlock(&rnp_old->fqslock);
		if (ret) {
2802
			rsp->n_force_qs_lh++;
2803 2804 2805 2806 2807
			return;
		}
		rnp_old = rnp;
	}
	/* rnp_old == rcu_get_root(rsp), rnp == NULL. */
2808

2809 2810
	/* Reached the root of the rcu_node tree, acquire lock. */
	raw_spin_lock_irqsave(&rnp_old->lock, flags);
2811
	smp_mb__after_unlock_lock();
2812
	raw_spin_unlock(&rnp_old->fqslock);
2813
	if (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
2814
		rsp->n_force_qs_lh++;
2815
		raw_spin_unlock_irqrestore(&rnp_old->lock, flags);
2816
		return;  /* Someone beat us to it. */
2817
	}
2818
	WRITE_ONCE(rsp->gp_flags, READ_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS);
2819
	raw_spin_unlock_irqrestore(&rnp_old->lock, flags);
2820
	rcu_gp_kthread_wake(rsp);
2821 2822 2823
}

/*
2824 2825 2826
 * This does the RCU core processing work for the specified rcu_state
 * and rcu_data structures.  This may be called only from the CPU to
 * whom the rdp belongs.
2827 2828
 */
static void
2829
__rcu_process_callbacks(struct rcu_state *rsp)
2830 2831
{
	unsigned long flags;
2832
	bool needwake;
2833
	struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
2834

2835 2836
	WARN_ON_ONCE(rdp->beenonline == 0);

2837 2838 2839 2840
	/* Update RCU state based on any recent quiescent states. */
	rcu_check_quiescent_state(rsp, rdp);

	/* Does this CPU require a not-yet-started grace period? */
2841
	local_irq_save(flags);
2842
	if (cpu_needs_another_gp(rsp, rdp)) {
2843
		raw_spin_lock(&rcu_get_root(rsp)->lock); /* irqs disabled. */
2844
		needwake = rcu_start_gp(rsp);
2845
		raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags);
2846 2847
		if (needwake)
			rcu_gp_kthread_wake(rsp);
2848 2849
	} else {
		local_irq_restore(flags);
2850 2851 2852
	}

	/* If there are callbacks ready, invoke them. */
2853
	if (cpu_has_callbacks_ready_to_invoke(rdp))
2854
		invoke_rcu_callbacks(rsp, rdp);
2855 2856 2857

	/* Do any needed deferred wakeups of rcuo kthreads. */
	do_nocb_deferred_wakeup(rdp);
2858 2859
}

2860
/*
2861
 * Do RCU core processing for the current CPU.
2862
 */
2863
static void rcu_process_callbacks(struct softirq_action *unused)
2864
{
2865 2866
	struct rcu_state *rsp;

2867 2868
	if (cpu_is_offline(smp_processor_id()))
		return;
2869
	trace_rcu_utilization(TPS("Start RCU core"));
2870 2871
	for_each_rcu_flavor(rsp)
		__rcu_process_callbacks(rsp);
2872
	trace_rcu_utilization(TPS("End RCU core"));
2873 2874
}

2875
/*
2876 2877 2878
 * Schedule RCU callback invocation.  If the specified type of RCU
 * does not support RCU priority boosting, just do a direct call,
 * otherwise wake up the per-CPU kernel kthread.  Note that because we
2879
 * are running on the current CPU with softirqs disabled, the
2880
 * rcu_cpu_kthread_task cannot disappear out from under us.
2881
 */
2882
static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
2883
{
2884
	if (unlikely(!READ_ONCE(rcu_scheduler_fully_active)))
2885
		return;
2886 2887
	if (likely(!rsp->boost)) {
		rcu_do_batch(rsp, rdp);
2888 2889
		return;
	}
2890
	invoke_rcu_callbacks_kthread();
2891 2892
}

2893
static void invoke_rcu_core(void)
2894
{
2895 2896
	if (cpu_online(smp_processor_id()))
		raise_softirq(RCU_SOFTIRQ);
2897 2898
}

2899 2900 2901 2902 2903
/*
 * Handle any core-RCU processing required by a call_rcu() invocation.
 */
static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
			    struct rcu_head *head, unsigned long flags)
2904
{
2905 2906
	bool needwake;

2907 2908 2909 2910
	/*
	 * If called from an extended quiescent state, invoke the RCU
	 * core in order to force a re-evaluation of RCU's idleness.
	 */
2911
	if (!rcu_is_watching())
2912 2913
		invoke_rcu_core();

2914
	/* If interrupts were disabled or CPU offline, don't invoke RCU core. */
2915
	if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
2916
		return;
2917

2918 2919 2920 2921 2922 2923 2924
	/*
	 * Force the grace period if too many callbacks or too long waiting.
	 * Enforce hysteresis, and don't invoke force_quiescent_state()
	 * if some other CPU has recently done so.  Also, don't bother
	 * invoking force_quiescent_state() if the newly enqueued callback
	 * is the only one waiting for a grace period to complete.
	 */
2925
	if (unlikely(rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) {
2926 2927

		/* Are we ignoring a completed grace period? */
2928
		note_gp_changes(rsp, rdp);
2929 2930 2931 2932 2933

		/* Start a new grace period if one not already started. */
		if (!rcu_gp_in_progress(rsp)) {
			struct rcu_node *rnp_root = rcu_get_root(rsp);

2934
			raw_spin_lock(&rnp_root->lock);
2935
			smp_mb__after_unlock_lock();
2936
			needwake = rcu_start_gp(rsp);
2937
			raw_spin_unlock(&rnp_root->lock);
2938 2939
			if (needwake)
				rcu_gp_kthread_wake(rsp);
2940 2941 2942 2943 2944
		} else {
			/* Give the grace period a kick. */
			rdp->blimit = LONG_MAX;
			if (rsp->n_force_qs == rdp->n_force_qs_snap &&
			    *rdp->nxttail[RCU_DONE_TAIL] != head)
2945
				force_quiescent_state(rsp);
2946 2947 2948
			rdp->n_force_qs_snap = rsp->n_force_qs;
			rdp->qlen_last_fqs_check = rdp->qlen;
		}
2949
	}
2950 2951
}

2952 2953 2954 2955 2956 2957 2958
/*
 * RCU callback function to leak a callback.
 */
static void rcu_leak_callback(struct rcu_head *rhp)
{
}

P
Paul E. McKenney 已提交
2959 2960 2961 2962 2963 2964
/*
 * Helper function for call_rcu() and friends.  The cpu argument will
 * normally be -1, indicating "currently running CPU".  It may specify
 * a CPU only if that CPU is a no-CBs CPU.  Currently, only _rcu_barrier()
 * is expected to specify a CPU.
 */
2965 2966
static void
__call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
P
Paul E. McKenney 已提交
2967
	   struct rcu_state *rsp, int cpu, bool lazy)
2968 2969 2970 2971
{
	unsigned long flags;
	struct rcu_data *rdp;

2972
	WARN_ON_ONCE((unsigned long)head & 0x1); /* Misaligned rcu_head! */
2973 2974
	if (debug_rcu_head_queue(head)) {
		/* Probable double call_rcu(), so leak the callback. */
2975
		WRITE_ONCE(head->func, rcu_leak_callback);
2976 2977 2978
		WARN_ONCE(1, "__call_rcu(): Leaked duplicate callback\n");
		return;
	}
2979 2980 2981 2982 2983 2984 2985 2986 2987 2988
	head->func = func;
	head->next = NULL;

	/*
	 * Opportunistically note grace-period endings and beginnings.
	 * Note that we might see a beginning right after we see an
	 * end, but never vice versa, since this CPU has to pass through
	 * a quiescent state betweentimes.
	 */
	local_irq_save(flags);
2989
	rdp = this_cpu_ptr(rsp->rda);
2990 2991

	/* Add the callback to our list. */
P
Paul E. McKenney 已提交
2992 2993 2994 2995 2996
	if (unlikely(rdp->nxttail[RCU_NEXT_TAIL] == NULL) || cpu != -1) {
		int offline;

		if (cpu != -1)
			rdp = per_cpu_ptr(rsp->rda, cpu);
2997 2998 2999 3000 3001 3002 3003 3004 3005 3006 3007 3008 3009
		if (likely(rdp->mynode)) {
			/* Post-boot, so this should be for a no-CBs CPU. */
			offline = !__call_rcu_nocb(rdp, head, lazy, flags);
			WARN_ON_ONCE(offline);
			/* Offline CPU, _call_rcu() illegal, leak callback.  */
			local_irq_restore(flags);
			return;
		}
		/*
		 * Very early boot, before rcu_init().  Initialize if needed
		 * and then drop through to queue the callback.
		 */
		BUG_ON(cpu != -1);
3010
		WARN_ON_ONCE(!rcu_is_watching());
3011 3012
		if (!likely(rdp->nxtlist))
			init_default_callback_list(rdp);
3013
	}
3014
	WRITE_ONCE(rdp->qlen, rdp->qlen + 1);
3015 3016
	if (lazy)
		rdp->qlen_lazy++;
3017 3018
	else
		rcu_idle_count_callbacks_posted();
3019 3020 3021
	smp_mb();  /* Count before adding callback for rcu_barrier(). */
	*rdp->nxttail[RCU_NEXT_TAIL] = head;
	rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
3022

3023 3024
	if (__is_kfree_rcu_offset((unsigned long)func))
		trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func,
3025
					 rdp->qlen_lazy, rdp->qlen);
3026
	else
3027
		trace_rcu_callback(rsp->name, head, rdp->qlen_lazy, rdp->qlen);
3028

3029 3030
	/* Go handle any RCU core processing required. */
	__call_rcu_core(rsp, rdp, head, flags);
3031 3032 3033 3034
	local_irq_restore(flags);
}

/*
3035
 * Queue an RCU-sched callback for invocation after a grace period.
3036
 */
3037
void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
3038
{
P
Paul E. McKenney 已提交
3039
	__call_rcu(head, func, &rcu_sched_state, -1, 0);
3040
}
3041
EXPORT_SYMBOL_GPL(call_rcu_sched);
3042 3043

/*
3044
 * Queue an RCU callback for invocation after a quicker grace period.
3045 3046 3047
 */
void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
{
P
Paul E. McKenney 已提交
3048
	__call_rcu(head, func, &rcu_bh_state, -1, 0);
3049 3050 3051
}
EXPORT_SYMBOL_GPL(call_rcu_bh);

3052 3053 3054 3055 3056 3057 3058 3059 3060 3061
/*
 * Queue an RCU callback for lazy invocation after a grace period.
 * This will likely be later named something like "call_rcu_lazy()",
 * but this change will require some way of tagging the lazy RCU
 * callbacks in the list of pending callbacks. Until then, this
 * function may only be called from __kfree_rcu().
 */
void kfree_call_rcu(struct rcu_head *head,
		    void (*func)(struct rcu_head *rcu))
{
3062
	__call_rcu(head, func, rcu_state_p, -1, 1);
3063 3064 3065
}
EXPORT_SYMBOL_GPL(kfree_call_rcu);

3066 3067 3068 3069 3070 3071 3072 3073 3074 3075 3076
/*
 * Because a context switch is a grace period for RCU-sched and RCU-bh,
 * any blocking grace-period wait automatically implies a grace period
 * if there is only one CPU online at any point time during execution
 * of either synchronize_sched() or synchronize_rcu_bh().  It is OK to
 * occasionally incorrectly indicate that there are multiple CPUs online
 * when there was in fact only one the whole time, as this just adds
 * some overhead: RCU still operates correctly.
 */
static inline int rcu_blocking_is_gp(void)
{
3077 3078
	int ret;

3079
	might_sleep();  /* Check for RCU read-side critical section. */
3080 3081 3082 3083
	preempt_disable();
	ret = num_online_cpus() <= 1;
	preempt_enable();
	return ret;
3084 3085
}

3086 3087 3088 3089 3090 3091 3092 3093 3094 3095 3096 3097
/**
 * synchronize_sched - wait until an rcu-sched grace period has elapsed.
 *
 * Control will return to the caller some time after a full rcu-sched
 * grace period has elapsed, in other words after all currently executing
 * rcu-sched read-side critical sections have completed.   These read-side
 * critical sections are delimited by rcu_read_lock_sched() and
 * rcu_read_unlock_sched(), and may be nested.  Note that preempt_disable(),
 * local_irq_disable(), and so on may be used in place of
 * rcu_read_lock_sched().
 *
 * This means that all preempt_disable code sequences, including NMI and
3098 3099 3100 3101 3102 3103 3104 3105 3106 3107 3108 3109 3110 3111 3112 3113 3114 3115 3116 3117 3118 3119
 * non-threaded hardware-interrupt handlers, in progress on entry will
 * have completed before this primitive returns.  However, this does not
 * guarantee that softirq handlers will have completed, since in some
 * kernels, these handlers can run in process context, and can block.
 *
 * Note that this guarantee implies further memory-ordering guarantees.
 * On systems with more than one CPU, when synchronize_sched() returns,
 * each CPU is guaranteed to have executed a full memory barrier since the
 * end of its last RCU-sched read-side critical section whose beginning
 * preceded the call to synchronize_sched().  In addition, each CPU having
 * an RCU read-side critical section that extends beyond the return from
 * synchronize_sched() is guaranteed to have executed a full memory barrier
 * after the beginning of synchronize_sched() and before the beginning of
 * that RCU read-side critical section.  Note that these guarantees include
 * CPUs that are offline, idle, or executing in user mode, as well as CPUs
 * that are executing in the kernel.
 *
 * Furthermore, if CPU A invoked synchronize_sched(), which returned
 * to its caller on CPU B, then both CPU A and CPU B are guaranteed
 * to have executed a full memory barrier during the execution of
 * synchronize_sched() -- even if CPU A and CPU B are the same CPU (but
 * again only if the system has more than one CPU).
3120 3121 3122 3123 3124 3125 3126 3127 3128
 *
 * This primitive provides the guarantees made by the (now removed)
 * synchronize_kernel() API.  In contrast, synchronize_rcu() only
 * guarantees that rcu_read_lock() sections will have completed.
 * In "classic RCU", these two guarantees happen to be one and
 * the same, but can differ in realtime RCU implementations.
 */
void synchronize_sched(void)
{
3129 3130 3131 3132
	rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
			   !lock_is_held(&rcu_lock_map) &&
			   !lock_is_held(&rcu_sched_lock_map),
			   "Illegal synchronize_sched() in RCU-sched read-side critical section");
3133 3134
	if (rcu_blocking_is_gp())
		return;
3135
	if (rcu_gp_is_expedited())
3136 3137 3138
		synchronize_sched_expedited();
	else
		wait_rcu_gp(call_rcu_sched);
3139 3140 3141 3142 3143 3144 3145 3146 3147 3148 3149
}
EXPORT_SYMBOL_GPL(synchronize_sched);

/**
 * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
 *
 * Control will return to the caller some time after a full rcu_bh grace
 * period has elapsed, in other words after all currently executing rcu_bh
 * read-side critical sections have completed.  RCU read-side critical
 * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
 * and may be nested.
3150 3151 3152
 *
 * See the description of synchronize_sched() for more detailed information
 * on memory ordering guarantees.
3153 3154 3155
 */
void synchronize_rcu_bh(void)
{
3156 3157 3158 3159
	rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
			   !lock_is_held(&rcu_lock_map) &&
			   !lock_is_held(&rcu_sched_lock_map),
			   "Illegal synchronize_rcu_bh() in RCU-bh read-side critical section");
3160 3161
	if (rcu_blocking_is_gp())
		return;
3162
	if (rcu_gp_is_expedited())
3163 3164 3165
		synchronize_rcu_bh_expedited();
	else
		wait_rcu_gp(call_rcu_bh);
3166 3167 3168
}
EXPORT_SYMBOL_GPL(synchronize_rcu_bh);

3169 3170 3171 3172 3173 3174 3175 3176 3177 3178 3179 3180 3181 3182 3183 3184 3185 3186 3187 3188
/**
 * get_state_synchronize_rcu - Snapshot current RCU state
 *
 * Returns a cookie that is used by a later call to cond_synchronize_rcu()
 * to determine whether or not a full grace period has elapsed in the
 * meantime.
 */
unsigned long get_state_synchronize_rcu(void)
{
	/*
	 * Any prior manipulation of RCU-protected data must happen
	 * before the load from ->gpnum.
	 */
	smp_mb();  /* ^^^ */

	/*
	 * Make sure this load happens before the purportedly
	 * time-consuming work between get_state_synchronize_rcu()
	 * and cond_synchronize_rcu().
	 */
3189
	return smp_load_acquire(&rcu_state_p->gpnum);
3190 3191 3192 3193 3194 3195 3196 3197 3198 3199 3200 3201 3202 3203 3204 3205 3206 3207 3208 3209 3210 3211 3212 3213 3214
}
EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);

/**
 * cond_synchronize_rcu - Conditionally wait for an RCU grace period
 *
 * @oldstate: return value from earlier call to get_state_synchronize_rcu()
 *
 * If a full RCU grace period has elapsed since the earlier call to
 * get_state_synchronize_rcu(), just return.  Otherwise, invoke
 * synchronize_rcu() to wait for a full grace period.
 *
 * Yes, this function does not take counter wrap into account.  But
 * counter wrap is harmless.  If the counter wraps, we have waited for
 * more than 2 billion grace periods (and way more on a 64-bit system!),
 * so waiting for one additional grace period should be just fine.
 */
void cond_synchronize_rcu(unsigned long oldstate)
{
	unsigned long newstate;

	/*
	 * Ensure that this load happens before any RCU-destructive
	 * actions the caller might carry out after we return.
	 */
3215
	newstate = smp_load_acquire(&rcu_state_p->completed);
3216 3217 3218 3219 3220
	if (ULONG_CMP_GE(oldstate, newstate))
		synchronize_rcu();
}
EXPORT_SYMBOL_GPL(cond_synchronize_rcu);

3221 3222 3223 3224 3225 3226 3227 3228 3229 3230 3231 3232 3233 3234 3235 3236 3237
static int synchronize_sched_expedited_cpu_stop(void *data)
{
	/*
	 * There must be a full memory barrier on each affected CPU
	 * between the time that try_stop_cpus() is called and the
	 * time that it returns.
	 *
	 * In the current initial implementation of cpu_stop, the
	 * above condition is already met when the control reaches
	 * this point and the following smp_mb() is not strictly
	 * necessary.  Do smp_mb() anyway for documentation and
	 * robustness against future implementation changes.
	 */
	smp_mb(); /* See above comment block. */
	return 0;
}

3238 3239 3240 3241 3242 3243 3244 3245 3246 3247
/**
 * synchronize_sched_expedited - Brute-force RCU-sched grace period
 *
 * Wait for an RCU-sched grace period to elapse, but use a "big hammer"
 * approach to force the grace period to end quickly.  This consumes
 * significant time on all CPUs and is unfriendly to real-time workloads,
 * so is thus not recommended for any sort of common-case code.  In fact,
 * if you are using synchronize_sched_expedited() in a loop, please
 * restructure your code to batch your updates, and then use a single
 * synchronize_sched() instead.
3248 3249 3250 3251 3252 3253 3254 3255 3256 3257 3258 3259 3260 3261 3262 3263 3264 3265 3266 3267 3268 3269 3270 3271
 *
 * This implementation can be thought of as an application of ticket
 * locking to RCU, with sync_sched_expedited_started and
 * sync_sched_expedited_done taking on the roles of the halves
 * of the ticket-lock word.  Each task atomically increments
 * sync_sched_expedited_started upon entry, snapshotting the old value,
 * then attempts to stop all the CPUs.  If this succeeds, then each
 * CPU will have executed a context switch, resulting in an RCU-sched
 * grace period.  We are then done, so we use atomic_cmpxchg() to
 * update sync_sched_expedited_done to match our snapshot -- but
 * only if someone else has not already advanced past our snapshot.
 *
 * On the other hand, if try_stop_cpus() fails, we check the value
 * of sync_sched_expedited_done.  If it has advanced past our
 * initial snapshot, then someone else must have forced a grace period
 * some time after we took our snapshot.  In this case, our work is
 * done for us, and we can simply return.  Otherwise, we try again,
 * but keep our initial snapshot for purposes of checking for someone
 * doing our work for us.
 *
 * If we fail too many times in a row, we fall back to synchronize_sched().
 */
void synchronize_sched_expedited(void)
{
3272 3273 3274
	cpumask_var_t cm;
	bool cma = false;
	int cpu;
3275 3276
	long firstsnap, s, snap;
	int trycount = 0;
3277
	struct rcu_state *rsp = &rcu_sched_state;
3278

3279 3280 3281 3282 3283 3284 3285 3286
	/*
	 * If we are in danger of counter wrap, just do synchronize_sched().
	 * By allowing sync_sched_expedited_started to advance no more than
	 * ULONG_MAX/8 ahead of sync_sched_expedited_done, we are ensuring
	 * that more than 3.5 billion CPUs would be required to force a
	 * counter wrap on a 32-bit system.  Quite a few more CPUs would of
	 * course be required on a 64-bit system.
	 */
3287 3288
	if (ULONG_CMP_GE((ulong)atomic_long_read(&rsp->expedited_start),
			 (ulong)atomic_long_read(&rsp->expedited_done) +
3289 3290
			 ULONG_MAX / 8)) {
		synchronize_sched();
3291
		atomic_long_inc(&rsp->expedited_wrap);
3292 3293
		return;
	}
3294

3295 3296 3297 3298
	/*
	 * Take a ticket.  Note that atomic_inc_return() implies a
	 * full memory barrier.
	 */
3299
	snap = atomic_long_inc_return(&rsp->expedited_start);
3300
	firstsnap = snap;
3301 3302 3303 3304 3305 3306
	if (!try_get_online_cpus()) {
		/* CPU hotplug operation in flight, fall back to normal GP. */
		wait_rcu_gp(call_rcu_sched);
		atomic_long_inc(&rsp->expedited_normal);
		return;
	}
3307
	WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id()));
3308

3309 3310 3311 3312 3313 3314 3315 3316 3317 3318 3319 3320 3321 3322 3323
	/* Offline CPUs, idle CPUs, and any CPU we run on are quiescent. */
	cma = zalloc_cpumask_var(&cm, GFP_KERNEL);
	if (cma) {
		cpumask_copy(cm, cpu_online_mask);
		cpumask_clear_cpu(raw_smp_processor_id(), cm);
		for_each_cpu(cpu, cm) {
			struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);

			if (!(atomic_add_return(0, &rdtp->dynticks) & 0x1))
				cpumask_clear_cpu(cpu, cm);
		}
		if (cpumask_weight(cm) == 0)
			goto all_cpus_idle;
	}

3324 3325 3326 3327
	/*
	 * Each pass through the following loop attempts to force a
	 * context switch on each CPU.
	 */
3328
	while (try_stop_cpus(cma ? cm : cpu_online_mask,
3329 3330 3331
			     synchronize_sched_expedited_cpu_stop,
			     NULL) == -EAGAIN) {
		put_online_cpus();
3332
		atomic_long_inc(&rsp->expedited_tryfail);
3333

3334
		/* Check to see if someone else did our work for us. */
3335
		s = atomic_long_read(&rsp->expedited_done);
3336
		if (ULONG_CMP_GE((ulong)s, (ulong)firstsnap)) {
3337
			/* ensure test happens before caller kfree */
3338
			smp_mb__before_atomic(); /* ^^^ */
3339
			atomic_long_inc(&rsp->expedited_workdone1);
3340
			free_cpumask_var(cm);
3341 3342
			return;
		}
3343 3344

		/* No joy, try again later.  Or just synchronize_sched(). */
3345
		if (trycount++ < 10) {
3346
			udelay(trycount * num_online_cpus());
3347
		} else {
3348
			wait_rcu_gp(call_rcu_sched);
3349
			atomic_long_inc(&rsp->expedited_normal);
3350
			free_cpumask_var(cm);
3351 3352 3353
			return;
		}

3354
		/* Recheck to see if someone else did our work for us. */
3355
		s = atomic_long_read(&rsp->expedited_done);
3356
		if (ULONG_CMP_GE((ulong)s, (ulong)firstsnap)) {
3357
			/* ensure test happens before caller kfree */
3358
			smp_mb__before_atomic(); /* ^^^ */
3359
			atomic_long_inc(&rsp->expedited_workdone2);
3360
			free_cpumask_var(cm);
3361 3362 3363 3364 3365
			return;
		}

		/*
		 * Refetching sync_sched_expedited_started allows later
3366 3367 3368 3369
		 * callers to piggyback on our grace period.  We retry
		 * after they started, so our grace period works for them,
		 * and they started after our first try, so their grace
		 * period works for us.
3370
		 */
3371 3372 3373 3374
		if (!try_get_online_cpus()) {
			/* CPU hotplug operation in flight, use normal GP. */
			wait_rcu_gp(call_rcu_sched);
			atomic_long_inc(&rsp->expedited_normal);
3375
			free_cpumask_var(cm);
3376 3377
			return;
		}
3378
		snap = atomic_long_read(&rsp->expedited_start);
3379 3380
		smp_mb(); /* ensure read is before try_stop_cpus(). */
	}
3381
	atomic_long_inc(&rsp->expedited_stoppedcpus);
3382

3383 3384 3385
all_cpus_idle:
	free_cpumask_var(cm);

3386 3387 3388 3389
	/*
	 * Everyone up to our most recent fetch is covered by our grace
	 * period.  Update the counter, but only if our work is still
	 * relevant -- which it won't be if someone who started later
3390
	 * than we did already did their update.
3391 3392
	 */
	do {
3393
		atomic_long_inc(&rsp->expedited_done_tries);
3394
		s = atomic_long_read(&rsp->expedited_done);
3395
		if (ULONG_CMP_GE((ulong)s, (ulong)snap)) {
3396
			/* ensure test happens before caller kfree */
3397
			smp_mb__before_atomic(); /* ^^^ */
3398
			atomic_long_inc(&rsp->expedited_done_lost);
3399 3400
			break;
		}
3401
	} while (atomic_long_cmpxchg(&rsp->expedited_done, s, snap) != s);
3402
	atomic_long_inc(&rsp->expedited_done_exit);
3403 3404 3405 3406 3407

	put_online_cpus();
}
EXPORT_SYMBOL_GPL(synchronize_sched_expedited);

3408 3409 3410 3411 3412 3413 3414 3415 3416
/*
 * Check to see if there is any immediate RCU-related work to be done
 * by the current CPU, for the specified type of RCU, returning 1 if so.
 * The checks are in order of increasing expense: checks that can be
 * carried out against CPU-local state are performed first.  However,
 * we must check for CPU stalls first, else we might not get a chance.
 */
static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
{
3417 3418
	struct rcu_node *rnp = rdp->mynode;

3419 3420 3421 3422 3423
	rdp->n_rcu_pending++;

	/* Check for CPU stalls, if enabled. */
	check_cpu_stall(rsp, rdp);

3424 3425 3426 3427
	/* Is this CPU a NO_HZ_FULL CPU that should ignore RCU? */
	if (rcu_nohz_full_cpu(rsp))
		return 0;

3428
	/* Is the RCU core waiting for a quiescent state from this CPU? */
3429
	if (rcu_scheduler_fully_active &&
3430 3431
	    rdp->qs_pending && !rdp->passed_quiesce &&
	    rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_qs_ctr)) {
3432
		rdp->n_rp_qs_pending++;
3433 3434 3435
	} else if (rdp->qs_pending &&
		   (rdp->passed_quiesce ||
		    rdp->rcu_qs_ctr_snap != __this_cpu_read(rcu_qs_ctr))) {
3436
		rdp->n_rp_report_qs++;
3437
		return 1;
3438
	}
3439 3440

	/* Does this CPU have callbacks ready to invoke? */
3441 3442
	if (cpu_has_callbacks_ready_to_invoke(rdp)) {
		rdp->n_rp_cb_ready++;
3443
		return 1;
3444
	}
3445 3446

	/* Has RCU gone idle with this CPU needing another grace period? */
3447 3448
	if (cpu_needs_another_gp(rsp, rdp)) {
		rdp->n_rp_cpu_needs_gp++;
3449
		return 1;
3450
	}
3451 3452

	/* Has another RCU grace period completed?  */
3453
	if (READ_ONCE(rnp->completed) != rdp->completed) { /* outside lock */
3454
		rdp->n_rp_gp_completed++;
3455
		return 1;
3456
	}
3457 3458

	/* Has a new RCU grace period started? */
3459 3460
	if (READ_ONCE(rnp->gpnum) != rdp->gpnum ||
	    unlikely(READ_ONCE(rdp->gpwrap))) { /* outside lock */
3461
		rdp->n_rp_gp_started++;
3462
		return 1;
3463
	}
3464

3465 3466 3467 3468 3469 3470
	/* Does this CPU need a deferred NOCB wakeup? */
	if (rcu_nocb_need_deferred_wakeup(rdp)) {
		rdp->n_rp_nocb_defer_wakeup++;
		return 1;
	}

3471
	/* nothing to do */
3472
	rdp->n_rp_need_nothing++;
3473 3474 3475 3476 3477 3478 3479 3480
	return 0;
}

/*
 * Check to see if there is any immediate RCU-related work to be done
 * by the current CPU, returning 1 if so.  This function is part of the
 * RCU implementation; it is -not- an exported member of the RCU API.
 */
3481
static int rcu_pending(void)
3482
{
3483 3484 3485
	struct rcu_state *rsp;

	for_each_rcu_flavor(rsp)
3486
		if (__rcu_pending(rsp, this_cpu_ptr(rsp->rda)))
3487 3488
			return 1;
	return 0;
3489 3490 3491
}

/*
3492 3493 3494
 * Return true if the specified CPU has any callback.  If all_lazy is
 * non-NULL, store an indication of whether all callbacks are lazy.
 * (If there are no callbacks, all of them are deemed to be lazy.)
3495
 */
3496
static int __maybe_unused rcu_cpu_has_callbacks(bool *all_lazy)
3497
{
3498 3499 3500
	bool al = true;
	bool hc = false;
	struct rcu_data *rdp;
3501 3502
	struct rcu_state *rsp;

3503
	for_each_rcu_flavor(rsp) {
3504
		rdp = this_cpu_ptr(rsp->rda);
3505 3506 3507 3508
		if (!rdp->nxtlist)
			continue;
		hc = true;
		if (rdp->qlen != rdp->qlen_lazy || !all_lazy) {
3509
			al = false;
3510 3511
			break;
		}
3512 3513 3514 3515
	}
	if (all_lazy)
		*all_lazy = al;
	return hc;
3516 3517
}

3518 3519 3520 3521
/*
 * Helper function for _rcu_barrier() tracing.  If tracing is disabled,
 * the compiler is expected to optimize this away.
 */
3522
static void _rcu_barrier_trace(struct rcu_state *rsp, const char *s,
3523 3524 3525 3526 3527 3528
			       int cpu, unsigned long done)
{
	trace_rcu_barrier(rsp->name, s, cpu,
			  atomic_read(&rsp->barrier_cpu_count), done);
}

3529 3530 3531 3532
/*
 * RCU callback function for _rcu_barrier().  If we are last, wake
 * up the task executing _rcu_barrier().
 */
3533
static void rcu_barrier_callback(struct rcu_head *rhp)
3534
{
3535 3536 3537
	struct rcu_data *rdp = container_of(rhp, struct rcu_data, barrier_head);
	struct rcu_state *rsp = rdp->rsp;

3538 3539
	if (atomic_dec_and_test(&rsp->barrier_cpu_count)) {
		_rcu_barrier_trace(rsp, "LastCB", -1, rsp->n_barrier_done);
3540
		complete(&rsp->barrier_completion);
3541 3542 3543
	} else {
		_rcu_barrier_trace(rsp, "CB", -1, rsp->n_barrier_done);
	}
3544 3545 3546 3547 3548 3549 3550
}

/*
 * Called with preemption disabled, and from cross-cpu IRQ context.
 */
static void rcu_barrier_func(void *type)
{
3551
	struct rcu_state *rsp = type;
3552
	struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
3553

3554
	_rcu_barrier_trace(rsp, "IRQ", -1, rsp->n_barrier_done);
3555
	atomic_inc(&rsp->barrier_cpu_count);
3556
	rsp->call(&rdp->barrier_head, rcu_barrier_callback);
3557 3558 3559 3560 3561 3562
}

/*
 * Orchestrate the specified type of RCU barrier, waiting for all
 * RCU callbacks of the specified type to complete.
 */
3563
static void _rcu_barrier(struct rcu_state *rsp)
3564
{
3565 3566
	int cpu;
	struct rcu_data *rdp;
3567
	unsigned long snap = READ_ONCE(rsp->n_barrier_done);
3568
	unsigned long snap_done;
3569

3570
	_rcu_barrier_trace(rsp, "Begin", -1, snap);
3571

3572
	/* Take mutex to serialize concurrent rcu_barrier() requests. */
3573
	mutex_lock(&rsp->barrier_mutex);
3574

3575 3576 3577 3578 3579 3580 3581 3582 3583 3584 3585 3586
	/*
	 * Ensure that all prior references, including to ->n_barrier_done,
	 * are ordered before the _rcu_barrier() machinery.
	 */
	smp_mb();  /* See above block comment. */

	/*
	 * Recheck ->n_barrier_done to see if others did our work for us.
	 * This means checking ->n_barrier_done for an even-to-odd-to-even
	 * transition.  The "if" expression below therefore rounds the old
	 * value up to the next even number and adds two before comparing.
	 */
3587
	snap_done = rsp->n_barrier_done;
3588
	_rcu_barrier_trace(rsp, "Check", -1, snap_done);
3589 3590 3591 3592 3593 3594 3595 3596 3597 3598 3599 3600

	/*
	 * If the value in snap is odd, we needed to wait for the current
	 * rcu_barrier() to complete, then wait for the next one, in other
	 * words, we need the value of snap_done to be three larger than
	 * the value of snap.  On the other hand, if the value in snap is
	 * even, we only had to wait for the next rcu_barrier() to complete,
	 * in other words, we need the value of snap_done to be only two
	 * greater than the value of snap.  The "(snap + 3) & ~0x1" computes
	 * this for us (thank you, Linus!).
	 */
	if (ULONG_CMP_GE(snap_done, (snap + 3) & ~0x1)) {
3601
		_rcu_barrier_trace(rsp, "EarlyExit", -1, snap_done);
3602 3603 3604 3605 3606 3607 3608
		smp_mb(); /* caller's subsequent code after above check. */
		mutex_unlock(&rsp->barrier_mutex);
		return;
	}

	/*
	 * Increment ->n_barrier_done to avoid duplicate work.  Use
3609
	 * WRITE_ONCE() to prevent the compiler from speculating
3610 3611
	 * the increment to precede the early-exit check.
	 */
3612
	WRITE_ONCE(rsp->n_barrier_done, rsp->n_barrier_done + 1);
3613
	WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 1);
3614
	_rcu_barrier_trace(rsp, "Inc1", -1, rsp->n_barrier_done);
3615
	smp_mb(); /* Order ->n_barrier_done increment with below mechanism. */
3616

3617
	/*
3618 3619
	 * Initialize the count to one rather than to zero in order to
	 * avoid a too-soon return to zero in case of a short grace period
3620 3621
	 * (or preemption of this task).  Exclude CPU-hotplug operations
	 * to ensure that no offline CPU has callbacks queued.
3622
	 */
3623
	init_completion(&rsp->barrier_completion);
3624
	atomic_set(&rsp->barrier_cpu_count, 1);
3625
	get_online_cpus();
3626 3627

	/*
3628 3629 3630
	 * Force each CPU with callbacks to register a new callback.
	 * When that callback is invoked, we will know that all of the
	 * corresponding CPU's preceding callbacks have been invoked.
3631
	 */
P
Paul E. McKenney 已提交
3632
	for_each_possible_cpu(cpu) {
3633
		if (!cpu_online(cpu) && !rcu_is_nocb_cpu(cpu))
P
Paul E. McKenney 已提交
3634
			continue;
3635
		rdp = per_cpu_ptr(rsp->rda, cpu);
3636
		if (rcu_is_nocb_cpu(cpu)) {
3637 3638 3639 3640 3641 3642
			if (!rcu_nocb_cpu_needs_barrier(rsp, cpu)) {
				_rcu_barrier_trace(rsp, "OfflineNoCB", cpu,
						   rsp->n_barrier_done);
			} else {
				_rcu_barrier_trace(rsp, "OnlineNoCB", cpu,
						   rsp->n_barrier_done);
3643
				smp_mb__before_atomic();
3644 3645 3646 3647
				atomic_inc(&rsp->barrier_cpu_count);
				__call_rcu(&rdp->barrier_head,
					   rcu_barrier_callback, rsp, cpu, 0);
			}
3648
		} else if (READ_ONCE(rdp->qlen)) {
3649 3650
			_rcu_barrier_trace(rsp, "OnlineQ", cpu,
					   rsp->n_barrier_done);
3651
			smp_call_function_single(cpu, rcu_barrier_func, rsp, 1);
3652
		} else {
3653 3654
			_rcu_barrier_trace(rsp, "OnlineNQ", cpu,
					   rsp->n_barrier_done);
3655 3656
		}
	}
3657
	put_online_cpus();
3658 3659 3660 3661 3662

	/*
	 * Now that we have an rcu_barrier_callback() callback on each
	 * CPU, and thus each counted, remove the initial count.
	 */
3663
	if (atomic_dec_and_test(&rsp->barrier_cpu_count))
3664
		complete(&rsp->barrier_completion);
3665

3666 3667
	/* Increment ->n_barrier_done to prevent duplicate work. */
	smp_mb(); /* Keep increment after above mechanism. */
3668
	WRITE_ONCE(rsp->n_barrier_done, rsp->n_barrier_done + 1);
3669
	WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 0);
3670
	_rcu_barrier_trace(rsp, "Inc2", -1, rsp->n_barrier_done);
3671 3672
	smp_mb(); /* Keep increment before caller's subsequent code. */

3673
	/* Wait for all rcu_barrier_callback() callbacks to be invoked. */
3674
	wait_for_completion(&rsp->barrier_completion);
3675 3676

	/* Other rcu_barrier() invocations can now safely proceed. */
3677
	mutex_unlock(&rsp->barrier_mutex);
3678 3679 3680 3681 3682 3683 3684
}

/**
 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
 */
void rcu_barrier_bh(void)
{
3685
	_rcu_barrier(&rcu_bh_state);
3686 3687 3688 3689 3690 3691 3692 3693
}
EXPORT_SYMBOL_GPL(rcu_barrier_bh);

/**
 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
 */
void rcu_barrier_sched(void)
{
3694
	_rcu_barrier(&rcu_sched_state);
3695 3696 3697
}
EXPORT_SYMBOL_GPL(rcu_barrier_sched);

3698 3699 3700 3701 3702 3703 3704 3705 3706 3707 3708 3709 3710 3711 3712 3713 3714 3715 3716 3717 3718 3719
/*
 * Propagate ->qsinitmask bits up the rcu_node tree to account for the
 * first CPU in a given leaf rcu_node structure coming online.  The caller
 * must hold the corresponding leaf rcu_node ->lock with interrrupts
 * disabled.
 */
static void rcu_init_new_rnp(struct rcu_node *rnp_leaf)
{
	long mask;
	struct rcu_node *rnp = rnp_leaf;

	for (;;) {
		mask = rnp->grpmask;
		rnp = rnp->parent;
		if (rnp == NULL)
			return;
		raw_spin_lock(&rnp->lock); /* Interrupts already disabled. */
		rnp->qsmaskinit |= mask;
		raw_spin_unlock(&rnp->lock); /* Interrupts remain disabled. */
	}
}

3720
/*
3721
 * Do boot-time initialization of a CPU's per-CPU RCU data.
3722
 */
3723 3724
static void __init
rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
3725 3726
{
	unsigned long flags;
3727
	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
3728 3729 3730
	struct rcu_node *rnp = rcu_get_root(rsp);

	/* Set up local state, ensuring consistent view of global state. */
P
Paul E. McKenney 已提交
3731
	raw_spin_lock_irqsave(&rnp->lock, flags);
3732 3733
	rdp->grpmask = 1UL << (cpu - rdp->mynode->grplo);
	rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
3734
	WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE);
3735
	WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1);
3736
	rdp->cpu = cpu;
3737
	rdp->rsp = rsp;
P
Paul E. McKenney 已提交
3738
	rcu_boot_init_nocb_percpu_data(rdp);
P
Paul E. McKenney 已提交
3739
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
3740 3741 3742 3743 3744 3745 3746
}

/*
 * Initialize a CPU's per-CPU RCU data.  Note that only one online or
 * offline event can be happening at a given time.  Note also that we
 * can accept some slop in the rsp->completed access due to the fact
 * that this CPU cannot possibly have any RCU callbacks in flight yet.
3747
 */
3748
static void
3749
rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
3750 3751 3752
{
	unsigned long flags;
	unsigned long mask;
3753
	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
3754 3755 3756
	struct rcu_node *rnp = rcu_get_root(rsp);

	/* Set up local state, ensuring consistent view of global state. */
P
Paul E. McKenney 已提交
3757
	raw_spin_lock_irqsave(&rnp->lock, flags);
3758
	rdp->beenonline = 1;	 /* We have now been online. */
3759 3760
	rdp->qlen_last_fqs_check = 0;
	rdp->n_force_qs_snap = rsp->n_force_qs;
3761
	rdp->blimit = blimit;
3762 3763
	if (!rdp->nxtlist)
		init_callback_list(rdp);  /* Re-enable callbacks on this CPU. */
3764
	rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
3765
	rcu_sysidle_init_percpu_data(rdp->dynticks);
3766 3767
	atomic_set(&rdp->dynticks->dynticks,
		   (atomic_read(&rdp->dynticks->dynticks) & ~0x1) + 1);
P
Paul E. McKenney 已提交
3768
	raw_spin_unlock(&rnp->lock);		/* irqs remain disabled. */
3769

3770 3771 3772 3773 3774
	/*
	 * Add CPU to leaf rcu_node pending-online bitmask.  Any needed
	 * propagation up the rcu_node tree will happen at the beginning
	 * of the next grace period.
	 */
3775 3776
	rnp = rdp->mynode;
	mask = rdp->grpmask;
3777 3778 3779 3780 3781 3782 3783 3784 3785 3786
	raw_spin_lock(&rnp->lock);		/* irqs already disabled. */
	smp_mb__after_unlock_lock();
	rnp->qsmaskinitnext |= mask;
	rdp->gpnum = rnp->completed; /* Make CPU later note any new GP. */
	rdp->completed = rnp->completed;
	rdp->passed_quiesce = false;
	rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_qs_ctr);
	rdp->qs_pending = false;
	trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuonl"));
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
3787 3788
}

3789
static void rcu_prepare_cpu(int cpu)
3790
{
3791 3792 3793
	struct rcu_state *rsp;

	for_each_rcu_flavor(rsp)
3794
		rcu_init_percpu_data(cpu, rsp);
3795 3796 3797
}

/*
3798
 * Handle CPU online/offline notification events.
3799
 */
3800 3801
int rcu_cpu_notify(struct notifier_block *self,
		   unsigned long action, void *hcpu)
3802 3803
{
	long cpu = (long)hcpu;
3804
	struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
3805
	struct rcu_node *rnp = rdp->mynode;
3806
	struct rcu_state *rsp;
3807 3808 3809 3810

	switch (action) {
	case CPU_UP_PREPARE:
	case CPU_UP_PREPARE_FROZEN:
P
Peter Zijlstra 已提交
3811 3812
		rcu_prepare_cpu(cpu);
		rcu_prepare_kthreads(cpu);
3813
		rcu_spawn_all_nocb_kthreads(cpu);
3814 3815
		break;
	case CPU_ONLINE:
3816
	case CPU_DOWN_FAILED:
T
Thomas Gleixner 已提交
3817
		rcu_boost_kthread_setaffinity(rnp, -1);
3818 3819
		break;
	case CPU_DOWN_PREPARE:
3820
		rcu_boost_kthread_setaffinity(rnp, cpu);
3821
		break;
3822 3823
	case CPU_DYING:
	case CPU_DYING_FROZEN:
3824 3825
		for_each_rcu_flavor(rsp)
			rcu_cleanup_dying_cpu(rsp);
3826
		break;
3827 3828 3829 3830 3831
	case CPU_DYING_IDLE:
		for_each_rcu_flavor(rsp) {
			rcu_cleanup_dying_idle_cpu(cpu, rsp);
		}
		break;
3832 3833 3834 3835
	case CPU_DEAD:
	case CPU_DEAD_FROZEN:
	case CPU_UP_CANCELED:
	case CPU_UP_CANCELED_FROZEN:
3836
		for_each_rcu_flavor(rsp) {
3837
			rcu_cleanup_dead_cpu(cpu, rsp);
3838 3839
			do_nocb_deferred_wakeup(per_cpu_ptr(rsp->rda, cpu));
		}
3840 3841 3842 3843
		break;
	default:
		break;
	}
3844
	return NOTIFY_OK;
3845 3846
}

3847 3848 3849 3850 3851 3852 3853
static int rcu_pm_notify(struct notifier_block *self,
			 unsigned long action, void *hcpu)
{
	switch (action) {
	case PM_HIBERNATION_PREPARE:
	case PM_SUSPEND_PREPARE:
		if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */
3854
			rcu_expedite_gp();
3855 3856 3857
		break;
	case PM_POST_HIBERNATION:
	case PM_POST_SUSPEND:
3858 3859
		if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */
			rcu_unexpedite_gp();
3860 3861 3862 3863 3864 3865 3866
		break;
	default:
		break;
	}
	return NOTIFY_OK;
}

3867
/*
3868
 * Spawn the kthreads that handle each RCU flavor's grace periods.
3869 3870 3871 3872
 */
static int __init rcu_spawn_gp_kthread(void)
{
	unsigned long flags;
3873
	int kthread_prio_in = kthread_prio;
3874 3875
	struct rcu_node *rnp;
	struct rcu_state *rsp;
3876
	struct sched_param sp;
3877 3878
	struct task_struct *t;

3879 3880 3881 3882 3883 3884 3885 3886 3887 3888 3889
	/* Force priority into range. */
	if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 1)
		kthread_prio = 1;
	else if (kthread_prio < 0)
		kthread_prio = 0;
	else if (kthread_prio > 99)
		kthread_prio = 99;
	if (kthread_prio != kthread_prio_in)
		pr_alert("rcu_spawn_gp_kthread(): Limited prio to %d from %d\n",
			 kthread_prio, kthread_prio_in);

3890
	rcu_scheduler_fully_active = 1;
3891
	for_each_rcu_flavor(rsp) {
3892
		t = kthread_create(rcu_gp_kthread, rsp, "%s", rsp->name);
3893 3894 3895 3896
		BUG_ON(IS_ERR(t));
		rnp = rcu_get_root(rsp);
		raw_spin_lock_irqsave(&rnp->lock, flags);
		rsp->gp_kthread = t;
3897 3898 3899 3900 3901
		if (kthread_prio) {
			sp.sched_priority = kthread_prio;
			sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
		}
		wake_up_process(t);
3902 3903
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
	}
3904
	rcu_spawn_nocb_kthreads();
3905
	rcu_spawn_boost_kthreads();
3906 3907 3908 3909
	return 0;
}
early_initcall(rcu_spawn_gp_kthread);

3910 3911 3912 3913 3914 3915 3916 3917 3918 3919 3920 3921 3922 3923 3924
/*
 * This function is invoked towards the end of the scheduler's initialization
 * process.  Before this is called, the idle task might contain
 * RCU read-side critical sections (during which time, this idle
 * task is booting the system).  After this function is called, the
 * idle tasks are prohibited from containing RCU read-side critical
 * sections.  This function also enables RCU lockdep checking.
 */
void rcu_scheduler_starting(void)
{
	WARN_ON(num_online_cpus() != 1);
	WARN_ON(nr_context_switches() > 0);
	rcu_scheduler_active = 1;
}

3925 3926 3927 3928 3929 3930 3931 3932
/*
 * Compute the per-level fanout, either using the exact fanout specified
 * or balancing the tree, depending on CONFIG_RCU_FANOUT_EXACT.
 */
static void __init rcu_init_levelspread(struct rcu_state *rsp)
{
	int i;

3933 3934 3935 3936 3937 3938 3939 3940 3941 3942 3943 3944 3945 3946
	if (IS_ENABLED(CONFIG_RCU_FANOUT_EXACT)) {
		rsp->levelspread[rcu_num_lvls - 1] = rcu_fanout_leaf;
		for (i = rcu_num_lvls - 2; i >= 0; i--)
			rsp->levelspread[i] = CONFIG_RCU_FANOUT;
	} else {
		int ccur;
		int cprv;

		cprv = nr_cpu_ids;
		for (i = rcu_num_lvls - 1; i >= 0; i--) {
			ccur = rsp->levelcnt[i];
			rsp->levelspread[i] = (cprv + ccur - 1) / ccur;
			cprv = ccur;
		}
3947 3948 3949 3950 3951 3952
	}
}

/*
 * Helper function for rcu_init() that initializes one rcu_state structure.
 */
3953 3954
static void __init rcu_init_one(struct rcu_state *rsp,
		struct rcu_data __percpu *rda)
3955
{
3956 3957 3958 3959 3960 3961 3962 3963 3964 3965
	static const char * const buf[] = {
		"rcu_node_0",
		"rcu_node_1",
		"rcu_node_2",
		"rcu_node_3" };  /* Match MAX_RCU_LVLS */
	static const char * const fqs[] = {
		"rcu_node_fqs_0",
		"rcu_node_fqs_1",
		"rcu_node_fqs_2",
		"rcu_node_fqs_3" };  /* Match MAX_RCU_LVLS */
3966
	static u8 fl_mask = 0x1;
3967 3968 3969 3970 3971
	int cpustride = 1;
	int i;
	int j;
	struct rcu_node *rnp;

3972 3973
	BUILD_BUG_ON(MAX_RCU_LVLS > ARRAY_SIZE(buf));  /* Fix buf[] init! */

3974 3975 3976 3977
	/* Silence gcc 4.8 warning about array index out of range. */
	if (rcu_num_lvls > RCU_NUM_LVLS)
		panic("rcu_init_one: rcu_num_lvls overflow");

3978 3979
	/* Initialize the level-tracking arrays. */

3980 3981 3982
	for (i = 0; i < rcu_num_lvls; i++)
		rsp->levelcnt[i] = num_rcu_lvl[i];
	for (i = 1; i < rcu_num_lvls; i++)
3983 3984
		rsp->level[i] = rsp->level[i - 1] + rsp->levelcnt[i - 1];
	rcu_init_levelspread(rsp);
3985 3986
	rsp->flavor_mask = fl_mask;
	fl_mask <<= 1;
3987 3988 3989

	/* Initialize the elements themselves, starting from the leaves. */

3990
	for (i = rcu_num_lvls - 1; i >= 0; i--) {
3991 3992 3993
		cpustride *= rsp->levelspread[i];
		rnp = rsp->level[i];
		for (j = 0; j < rsp->levelcnt[i]; j++, rnp++) {
P
Paul E. McKenney 已提交
3994
			raw_spin_lock_init(&rnp->lock);
3995 3996
			lockdep_set_class_and_name(&rnp->lock,
						   &rcu_node_class[i], buf[i]);
3997 3998 3999
			raw_spin_lock_init(&rnp->fqslock);
			lockdep_set_class_and_name(&rnp->fqslock,
						   &rcu_fqs_class[i], fqs[i]);
4000 4001
			rnp->gpnum = rsp->gpnum;
			rnp->completed = rsp->completed;
4002 4003 4004 4005
			rnp->qsmask = 0;
			rnp->qsmaskinit = 0;
			rnp->grplo = j * cpustride;
			rnp->grphi = (j + 1) * cpustride - 1;
4006 4007
			if (rnp->grphi >= nr_cpu_ids)
				rnp->grphi = nr_cpu_ids - 1;
4008 4009 4010 4011 4012 4013 4014 4015 4016 4017 4018
			if (i == 0) {
				rnp->grpnum = 0;
				rnp->grpmask = 0;
				rnp->parent = NULL;
			} else {
				rnp->grpnum = j % rsp->levelspread[i - 1];
				rnp->grpmask = 1UL << rnp->grpnum;
				rnp->parent = rsp->level[i - 1] +
					      j / rsp->levelspread[i - 1];
			}
			rnp->level = i;
4019
			INIT_LIST_HEAD(&rnp->blkd_tasks);
4020
			rcu_init_one_nocb(rnp);
4021 4022
		}
	}
4023

4024
	init_waitqueue_head(&rsp->gp_wq);
4025
	rnp = rsp->level[rcu_num_lvls - 1];
4026
	for_each_possible_cpu(i) {
4027
		while (i > rnp->grphi)
4028
			rnp++;
4029
		per_cpu_ptr(rsp->rda, i)->mynode = rnp;
4030 4031
		rcu_boot_init_percpu_data(i, rsp);
	}
4032
	list_add(&rsp->flavors, &rcu_struct_flavors);
4033 4034
}

4035 4036
/*
 * Compute the rcu_node tree geometry from kernel parameters.  This cannot
4037
 * replace the definitions in tree.h because those are needed to size
4038 4039 4040 4041
 * the ->node array in the rcu_state structure.
 */
static void __init rcu_init_geometry(void)
{
4042
	ulong d;
4043 4044
	int i;
	int j;
4045
	int n = nr_cpu_ids;
4046 4047
	int rcu_capacity[MAX_RCU_LVLS + 1];

4048 4049 4050 4051 4052 4053 4054 4055 4056 4057 4058 4059 4060
	/*
	 * Initialize any unspecified boot parameters.
	 * The default values of jiffies_till_first_fqs and
	 * jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS
	 * value, which is a function of HZ, then adding one for each
	 * RCU_JIFFIES_FQS_DIV CPUs that might be on the system.
	 */
	d = RCU_JIFFIES_TILL_FORCE_QS + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
	if (jiffies_till_first_fqs == ULONG_MAX)
		jiffies_till_first_fqs = d;
	if (jiffies_till_next_fqs == ULONG_MAX)
		jiffies_till_next_fqs = d;

4061
	/* If the compile-time values are accurate, just leave. */
4062 4063
	if (rcu_fanout_leaf == CONFIG_RCU_FANOUT_LEAF &&
	    nr_cpu_ids == NR_CPUS)
4064
		return;
4065 4066
	pr_info("RCU: Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%d\n",
		rcu_fanout_leaf, nr_cpu_ids);
4067 4068 4069 4070 4071 4072 4073 4074 4075 4076 4077 4078 4079 4080 4081 4082 4083 4084 4085 4086 4087 4088 4089 4090 4091 4092 4093 4094 4095 4096 4097 4098 4099 4100 4101 4102 4103 4104 4105 4106 4107 4108 4109 4110 4111

	/*
	 * Compute number of nodes that can be handled an rcu_node tree
	 * with the given number of levels.  Setting rcu_capacity[0] makes
	 * some of the arithmetic easier.
	 */
	rcu_capacity[0] = 1;
	rcu_capacity[1] = rcu_fanout_leaf;
	for (i = 2; i <= MAX_RCU_LVLS; i++)
		rcu_capacity[i] = rcu_capacity[i - 1] * CONFIG_RCU_FANOUT;

	/*
	 * The boot-time rcu_fanout_leaf parameter is only permitted
	 * to increase the leaf-level fanout, not decrease it.  Of course,
	 * the leaf-level fanout cannot exceed the number of bits in
	 * the rcu_node masks.  Finally, the tree must be able to accommodate
	 * the configured number of CPUs.  Complain and fall back to the
	 * compile-time values if these limits are exceeded.
	 */
	if (rcu_fanout_leaf < CONFIG_RCU_FANOUT_LEAF ||
	    rcu_fanout_leaf > sizeof(unsigned long) * 8 ||
	    n > rcu_capacity[MAX_RCU_LVLS]) {
		WARN_ON(1);
		return;
	}

	/* Calculate the number of rcu_nodes at each level of the tree. */
	for (i = 1; i <= MAX_RCU_LVLS; i++)
		if (n <= rcu_capacity[i]) {
			for (j = 0; j <= i; j++)
				num_rcu_lvl[j] =
					DIV_ROUND_UP(n, rcu_capacity[i - j]);
			rcu_num_lvls = i;
			for (j = i + 1; j <= MAX_RCU_LVLS; j++)
				num_rcu_lvl[j] = 0;
			break;
		}

	/* Calculate the total number of rcu_node structures. */
	rcu_num_nodes = 0;
	for (i = 0; i <= MAX_RCU_LVLS; i++)
		rcu_num_nodes += num_rcu_lvl[i];
	rcu_num_nodes -= n;
}

4112
void __init rcu_init(void)
4113
{
P
Paul E. McKenney 已提交
4114
	int cpu;
4115

4116 4117
	rcu_early_boot_tests();

4118
	rcu_bootup_announce();
4119
	rcu_init_geometry();
4120
	rcu_init_one(&rcu_bh_state, &rcu_bh_data);
4121
	rcu_init_one(&rcu_sched_state, &rcu_sched_data);
4122
	__rcu_init_preempt();
J
Jiang Fang 已提交
4123
	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
4124 4125 4126 4127 4128 4129 4130

	/*
	 * We don't need protection against CPU-hotplug here because
	 * this is called early in boot, before either interrupts
	 * or the scheduler are operational.
	 */
	cpu_notifier(rcu_cpu_notify, 0);
4131
	pm_notifier(rcu_pm_notify, 0);
P
Paul E. McKenney 已提交
4132 4133
	for_each_online_cpu(cpu)
		rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
4134 4135
}

4136
#include "tree_plugin.h"