tree.c 123.7 KB
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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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struct rcu_state sname##_state = { \
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	.level = { &sname##_state.node[0] }, \
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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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	.onoff_mutex = __MUTEX_INITIALIZER(sname##_state.onoff_mutex), \
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	.name = RCU_STATE_NAME(sname), \
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	.abbr = sabbr, \
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}; \
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DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, sname##_data)
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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_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. */
static int gp_init_delay = IS_ENABLED(CONFIG_RCU_TORTURE_TEST_SLOW_INIT)
				? CONFIG_RCU_TORTURE_TEST_SLOW_INIT_DELAY
				: 0;
module_param(gp_init_delay, int, 0644);

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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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/*
 * Return true if an RCU grace period is in progress.  The ACCESS_ONCE()s
 * 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)
{
	return ACCESS_ONCE(rsp->completed) != ACCESS_ONCE(rsp->gpnum);
}

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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. */
		if (ACCESS_ONCE(rdp->mynode->completed) !=
		    ACCESS_ONCE(rdp->cond_resched_completed))
			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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/*
 * Register a quiesecent state for all RCU flavors.  If there is an
 * emergency, invoke rcu_momentary_dyntick_idle() to do a heavy-weight
 * dyntick-idle quiescent state visible to other CPUs (but only for those
 * RCU flavors in desparate need of a quiescent state, which will normally
 * 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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/*
 * 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) {
		*flags = ACCESS_ONCE(rsp->gp_flags);
		*gpnum = ACCESS_ONCE(rsp->gpnum);
		*completed = ACCESS_ONCE(rsp->completed);
		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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/*
 * Force a quiescent state for RCU-sched.
 */
void rcu_sched_force_quiescent_state(void)
{
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	force_quiescent_state(&rcu_sched_state);
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}
EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state);

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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);
	int idx = (ACCESS_ONCE(rnp->completed) + 1) & 0x1;
	int *fp = &rnp->need_future_gp[idx];

	return ACCESS_ONCE(*fp);
}

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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] &&
		    ULONG_CMP_LT(ACCESS_ONCE(rsp->completed),
				 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)) {
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		struct task_struct *idle __maybe_unused =
			idle_task(smp_processor_id());
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		trace_rcu_dyntick(TPS("Error on entry: not idle task"), oldval, 0);
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		ftrace_dump(DUMP_ORIG);
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		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! */
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	}
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	for_each_rcu_flavor(rsp) {
		rdp = this_cpu_ptr(rsp->rda);
		do_nocb_deferred_wakeup(rdp);
	}
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	rcu_prepare_for_idle();
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	/* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
588
	smp_mb__before_atomic();  /* See above. */
589
	atomic_inc(&rdtp->dynticks);
590
	smp_mb__after_atomic();  /* Force ordering with next sojourn. */
591
	WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
592
	rcu_dynticks_task_enter();
593 594

	/*
595
	 * It is illegal to enter an extended quiescent state while
596 597 598 599 600 601 602 603
	 * 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.");
604
}
605

606 607 608
/*
 * Enter an RCU extended quiescent state, which can be either the
 * idle loop or adaptive-tickless usermode execution.
609
 */
610
static void rcu_eqs_enter(bool user)
611
{
612
	long long oldval;
613 614
	struct rcu_dynticks *rdtp;

615
	rdtp = this_cpu_ptr(&rcu_dynticks);
616
	oldval = rdtp->dynticks_nesting;
617
	WARN_ON_ONCE((oldval & DYNTICK_TASK_NEST_MASK) == 0);
618
	if ((oldval & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE) {
619
		rdtp->dynticks_nesting = 0;
620
		rcu_eqs_enter_common(oldval, user);
621
	} else {
622
		rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE;
623
	}
624
}
625 626 627 628 629 630 631 632 633 634 635 636 637 638 639

/**
 * 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)
{
640 641 642
	unsigned long flags;

	local_irq_save(flags);
643
	rcu_eqs_enter(false);
644
	rcu_sysidle_enter(0);
645
	local_irq_restore(flags);
646
}
647
EXPORT_SYMBOL_GPL(rcu_idle_enter);
648

649
#ifdef CONFIG_RCU_USER_QS
650 651 652 653 654 655 656 657 658 659
/**
 * 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)
{
660
	rcu_eqs_enter(1);
661
}
662
#endif /* CONFIG_RCU_USER_QS */
663

664 665 666 667 668 669
/**
 * 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.
670
 *
671 672 673 674 675 676 677 678
 * 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.
679
 */
680
void rcu_irq_exit(void)
681 682
{
	unsigned long flags;
683
	long long oldval;
684 685 686
	struct rcu_dynticks *rdtp;

	local_irq_save(flags);
687
	rdtp = this_cpu_ptr(&rcu_dynticks);
688
	oldval = rdtp->dynticks_nesting;
689 690
	rdtp->dynticks_nesting--;
	WARN_ON_ONCE(rdtp->dynticks_nesting < 0);
691
	if (rdtp->dynticks_nesting)
692
		trace_rcu_dyntick(TPS("--="), oldval, rdtp->dynticks_nesting);
693
	else
694 695
		rcu_eqs_enter_common(oldval, true);
	rcu_sysidle_enter(1);
696 697 698 699
	local_irq_restore(flags);
}

/*
700
 * rcu_eqs_exit_common - current CPU moving away from extended quiescent state
701 702 703 704 705
 *
 * 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.
 */
706
static void rcu_eqs_exit_common(long long oldval, int user)
707
{
708 709
	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);

710
	rcu_dynticks_task_exit();
711
	smp_mb__before_atomic();  /* Force ordering w/previous sojourn. */
712 713
	atomic_inc(&rdtp->dynticks);
	/* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
714
	smp_mb__after_atomic();  /* See above. */
715
	WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
716
	rcu_cleanup_after_idle();
717
	trace_rcu_dyntick(TPS("End"), oldval, rdtp->dynticks_nesting);
718
	if (!user && !is_idle_task(current)) {
719 720
		struct task_struct *idle __maybe_unused =
			idle_task(smp_processor_id());
721

722
		trace_rcu_dyntick(TPS("Error on exit: not idle task"),
723
				  oldval, rdtp->dynticks_nesting);
724
		ftrace_dump(DUMP_ORIG);
725 726 727
		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! */
728 729 730
	}
}

731 732 733
/*
 * Exit an RCU extended quiescent state, which can be either the
 * idle loop or adaptive-tickless usermode execution.
734
 */
735
static void rcu_eqs_exit(bool user)
736 737 738 739
{
	struct rcu_dynticks *rdtp;
	long long oldval;

740
	rdtp = this_cpu_ptr(&rcu_dynticks);
741
	oldval = rdtp->dynticks_nesting;
742
	WARN_ON_ONCE(oldval < 0);
743
	if (oldval & DYNTICK_TASK_NEST_MASK) {
744
		rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
745
	} else {
746
		rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
747
		rcu_eqs_exit_common(oldval, user);
748
	}
749
}
750 751 752 753 754 755 756 757 758 759 760 761 762 763

/**
 * 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)
{
764 765 766
	unsigned long flags;

	local_irq_save(flags);
767
	rcu_eqs_exit(false);
768
	rcu_sysidle_exit(0);
769
	local_irq_restore(flags);
770
}
771
EXPORT_SYMBOL_GPL(rcu_idle_exit);
772

773
#ifdef CONFIG_RCU_USER_QS
774 775 776 777 778 779 780 781
/**
 * 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)
{
782
	rcu_eqs_exit(1);
783
}
784
#endif /* CONFIG_RCU_USER_QS */
785

786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811
/**
 * 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);
812
	rdtp = this_cpu_ptr(&rcu_dynticks);
813 814 815
	oldval = rdtp->dynticks_nesting;
	rdtp->dynticks_nesting++;
	WARN_ON_ONCE(rdtp->dynticks_nesting == 0);
816
	if (oldval)
817
		trace_rcu_dyntick(TPS("++="), oldval, rdtp->dynticks_nesting);
818
	else
819 820
		rcu_eqs_exit_common(oldval, true);
	rcu_sysidle_exit(1);
821 822 823 824 825 826
	local_irq_restore(flags);
}

/**
 * rcu_nmi_enter - inform RCU of entry to NMI context
 *
827 828 829 830 831
 * 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.)
832 833 834
 */
void rcu_nmi_enter(void)
{
835
	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
836
	int incby = 2;
837

838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858
	/* 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();
859 860 861 862 863
}

/**
 * rcu_nmi_exit - inform RCU of exit from NMI context
 *
864 865 866 867
 * 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.
868 869 870
 */
void rcu_nmi_exit(void)
{
871
	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
872

873 874 875 876 877 878 879 880 881 882 883 884 885 886
	/*
	 * 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;
887
		return;
888 889 890 891
	}

	/* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
	rdtp->dynticks_nmi_nesting = 0;
892
	/* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
893
	smp_mb__before_atomic();  /* See above. */
894
	atomic_inc(&rdtp->dynticks);
895
	smp_mb__after_atomic();  /* Force delay to next write. */
896
	WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
897 898 899
}

/**
900 901 902 903 904 905 906
 * __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.
 */
907
bool notrace __rcu_is_watching(void)
908 909 910 911 912 913
{
	return atomic_read(this_cpu_ptr(&rcu_dynticks.dynticks)) & 0x1;
}

/**
 * rcu_is_watching - see if RCU thinks that the current CPU is idle
914
 *
915
 * If the current CPU is in its idle loop and is neither in an interrupt
916
 * or NMI handler, return true.
917
 */
918
bool notrace rcu_is_watching(void)
919
{
920
	bool ret;
921 922

	preempt_disable();
923
	ret = __rcu_is_watching();
924 925
	preempt_enable();
	return ret;
926
}
927
EXPORT_SYMBOL_GPL(rcu_is_watching);
928

929
#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
930 931 932 933 934 935 936

/*
 * 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
937 938 939 940 941 942 943 944 945 946 947
 * 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.
948 949 950 951 952 953
 *
 * Disable checking if in an NMI handler because we cannot safely report
 * errors from NMI handlers anyway.
 */
bool rcu_lockdep_current_cpu_online(void)
{
954 955
	struct rcu_data *rdp;
	struct rcu_node *rnp;
956 957 958
	bool ret;

	if (in_nmi())
F
Fengguang Wu 已提交
959
		return true;
960
	preempt_disable();
961
	rdp = this_cpu_ptr(&rcu_sched_data);
962 963
	rnp = rdp->mynode;
	ret = (rdp->grpmask & rnp->qsmaskinit) ||
964 965 966 967 968 969
	      !rcu_scheduler_fully_active;
	preempt_enable();
	return ret;
}
EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);

970
#endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
971

972
/**
973
 * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle
974
 *
975 976 977
 * 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.
978
 */
979
static int rcu_is_cpu_rrupt_from_idle(void)
980
{
981
	return __this_cpu_read(rcu_dynticks.dynticks_nesting) <= 1;
982 983 984 985 986
}

/*
 * Snapshot the specified CPU's dynticks counter so that we can later
 * credit them with an implicit quiescent state.  Return 1 if this CPU
987
 * is in dynticks idle mode, which is an extended quiescent state.
988
 */
989 990
static int dyntick_save_progress_counter(struct rcu_data *rdp,
					 bool *isidle, unsigned long *maxj)
991
{
992
	rdp->dynticks_snap = atomic_add_return(0, &rdp->dynticks->dynticks);
993
	rcu_sysidle_check_cpu(rdp, isidle, maxj);
994 995 996 997
	if ((rdp->dynticks_snap & 0x1) == 0) {
		trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
		return 1;
	} else {
998 999 1000
		if (ULONG_CMP_LT(ACCESS_ONCE(rdp->gpnum) + ULONG_MAX / 4,
				 rdp->mynode->gpnum))
			ACCESS_ONCE(rdp->gpwrap) = true;
1001 1002
		return 0;
	}
1003 1004 1005 1006 1007 1008
}

/*
 * 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()
1009
 * for this same CPU, or by virtue of having been offline.
1010
 */
1011 1012
static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
				    bool *isidle, unsigned long *maxj)
1013
{
1014
	unsigned int curr;
1015
	int *rcrmp;
1016
	unsigned int snap;
1017

1018 1019
	curr = (unsigned int)atomic_add_return(0, &rdp->dynticks->dynticks);
	snap = (unsigned int)rdp->dynticks_snap;
1020 1021 1022 1023 1024 1025 1026 1027 1028

	/*
	 * 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.
	 */
1029
	if ((curr & 0x1) == 0 || UINT_CMP_GE(curr, snap + 2)) {
1030
		trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
1031 1032 1033 1034
		rdp->dynticks_fqs++;
		return 1;
	}

1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049
	/*
	 * 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)) {
1050
		trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("ofl"));
1051 1052 1053
		rdp->offline_fqs++;
		return 1;
	}
1054 1055

	/*
1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074
	 * 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.
1075
	 */
1076 1077 1078
	rcrmp = &per_cpu(rcu_sched_qs_mask, rdp->cpu);
	if (ULONG_CMP_GE(jiffies,
			 rdp->rsp->gp_start + jiffies_till_sched_qs) ||
1079
	    ULONG_CMP_GE(jiffies, rdp->rsp->jiffies_resched)) {
1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092
		if (!(ACCESS_ONCE(*rcrmp) & rdp->rsp->flavor_mask)) {
			ACCESS_ONCE(rdp->cond_resched_completed) =
				ACCESS_ONCE(rdp->mynode->completed);
			smp_mb(); /* ->cond_resched_completed before *rcrmp. */
			ACCESS_ONCE(*rcrmp) =
				ACCESS_ONCE(*rcrmp) + rdp->rsp->flavor_mask;
			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. */
		}
1093 1094
	}

1095
	return 0;
1096 1097 1098 1099
}

static void record_gp_stall_check_time(struct rcu_state *rsp)
{
1100
	unsigned long j = jiffies;
1101
	unsigned long j1;
1102 1103 1104

	rsp->gp_start = j;
	smp_wmb(); /* Record start time before stall time. */
1105
	j1 = rcu_jiffies_till_stall_check();
1106
	ACCESS_ONCE(rsp->jiffies_stall) = j + j1;
1107
	rsp->jiffies_resched = j + j1 / 2;
1108
	rsp->n_force_qs_gpstart = ACCESS_ONCE(rsp->n_force_qs);
1109 1110
}

1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123
/*
 * 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;
	gpa = ACCESS_ONCE(rsp->gp_activity);
	if (j - gpa > 2 * HZ)
		pr_err("%s kthread starved for %ld jiffies!\n",
		       rsp->name, j - gpa);
1124 1125
}

1126
/*
1127
 * Dump stacks of all tasks running on stalled CPUs.
1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145
 */
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);
	}
}

1146
static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum)
1147 1148 1149 1150
{
	int cpu;
	long delta;
	unsigned long flags;
1151 1152
	unsigned long gpa;
	unsigned long j;
1153
	int ndetected = 0;
1154
	struct rcu_node *rnp = rcu_get_root(rsp);
1155
	long totqlen = 0;
1156 1157 1158

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

P
Paul E. McKenney 已提交
1159
	raw_spin_lock_irqsave(&rnp->lock, flags);
1160
	delta = jiffies - ACCESS_ONCE(rsp->jiffies_stall);
1161
	if (delta < RCU_STALL_RAT_DELAY || !rcu_gp_in_progress(rsp)) {
P
Paul E. McKenney 已提交
1162
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
1163 1164
		return;
	}
1165
	ACCESS_ONCE(rsp->jiffies_stall) = jiffies + 3 * rcu_jiffies_till_stall_check() + 3;
P
Paul E. McKenney 已提交
1166
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
1167

1168 1169 1170 1171 1172
	/*
	 * OK, time to rat on our buddy...
	 * See Documentation/RCU/stallwarn.txt for info on how to debug
	 * RCU CPU stall warnings.
	 */
1173
	pr_err("INFO: %s detected stalls on CPUs/tasks:",
1174
	       rsp->name);
1175
	print_cpu_stall_info_begin();
1176
	rcu_for_each_leaf_node(rsp, rnp) {
1177
		raw_spin_lock_irqsave(&rnp->lock, flags);
1178
		ndetected += rcu_print_task_stall(rnp);
1179 1180 1181 1182 1183 1184 1185 1186
		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++;
				}
		}
1187
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
1188
	}
1189 1190

	print_cpu_stall_info_end();
1191 1192
	for_each_possible_cpu(cpu)
		totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen;
1193
	pr_cont("(detected by %d, t=%ld jiffies, g=%ld, c=%ld, q=%lu)\n",
1194
	       smp_processor_id(), (long)(jiffies - rsp->gp_start),
1195
	       (long)rsp->gpnum, (long)rsp->completed, totqlen);
1196
	if (ndetected) {
1197
		rcu_dump_cpu_stacks(rsp);
1198 1199 1200 1201 1202 1203 1204
	} else {
		if (ACCESS_ONCE(rsp->gpnum) != gpnum ||
		    ACCESS_ONCE(rsp->completed) == gpnum) {
			pr_err("INFO: Stall ended before state dump start\n");
		} else {
			j = jiffies;
			gpa = ACCESS_ONCE(rsp->gp_activity);
1205
			pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld, root ->qsmask %#lx\n",
1206
			       rsp->name, j - gpa, j, gpa,
1207 1208
			       jiffies_till_next_fqs,
			       rcu_get_root(rsp)->qsmask);
1209 1210 1211 1212
			/* In this case, the current CPU might be at fault. */
			sched_show_task(current);
		}
	}
1213

1214
	/* Complain about tasks blocking the grace period. */
1215 1216
	rcu_print_detail_task_stall(rsp);

1217 1218
	rcu_check_gp_kthread_starvation(rsp);

1219
	force_quiescent_state(rsp);  /* Kick them all. */
1220 1221 1222 1223
}

static void print_cpu_stall(struct rcu_state *rsp)
{
1224
	int cpu;
1225 1226
	unsigned long flags;
	struct rcu_node *rnp = rcu_get_root(rsp);
1227
	long totqlen = 0;
1228

1229 1230 1231 1232 1233
	/*
	 * OK, time to rat on ourselves...
	 * See Documentation/RCU/stallwarn.txt for info on how to debug
	 * RCU CPU stall warnings.
	 */
1234
	pr_err("INFO: %s self-detected stall on CPU", rsp->name);
1235 1236 1237
	print_cpu_stall_info_begin();
	print_cpu_stall_info(rsp, smp_processor_id());
	print_cpu_stall_info_end();
1238 1239
	for_each_possible_cpu(cpu)
		totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen;
1240 1241 1242
	pr_cont(" (t=%lu jiffies g=%ld c=%ld q=%lu)\n",
		jiffies - rsp->gp_start,
		(long)rsp->gpnum, (long)rsp->completed, totqlen);
1243 1244 1245

	rcu_check_gp_kthread_starvation(rsp);

1246
	rcu_dump_cpu_stacks(rsp);
1247

P
Paul E. McKenney 已提交
1248
	raw_spin_lock_irqsave(&rnp->lock, flags);
1249 1250
	if (ULONG_CMP_GE(jiffies, ACCESS_ONCE(rsp->jiffies_stall)))
		ACCESS_ONCE(rsp->jiffies_stall) = jiffies +
1251
				     3 * rcu_jiffies_till_stall_check() + 3;
P
Paul E. McKenney 已提交
1252
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
1253

1254 1255 1256 1257 1258 1259 1260 1261
	/*
	 * 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());
1262 1263 1264 1265
}

static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
{
1266 1267 1268
	unsigned long completed;
	unsigned long gpnum;
	unsigned long gps;
1269 1270
	unsigned long j;
	unsigned long js;
1271 1272
	struct rcu_node *rnp;

1273
	if (rcu_cpu_stall_suppress || !rcu_gp_in_progress(rsp))
1274
		return;
1275
	j = jiffies;
1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295

	/*
	 * 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.
	 */
	gpnum = ACCESS_ONCE(rsp->gpnum);
	smp_rmb(); /* Pick up ->gpnum first... */
1296
	js = ACCESS_ONCE(rsp->jiffies_stall);
1297 1298 1299 1300 1301 1302 1303 1304
	smp_rmb(); /* ...then ->jiffies_stall before the rest... */
	gps = ACCESS_ONCE(rsp->gp_start);
	smp_rmb(); /* ...and finally ->gp_start before ->completed. */
	completed = ACCESS_ONCE(rsp->completed);
	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. */
1305
	rnp = rdp->mynode;
1306
	if (rcu_gp_in_progress(rsp) &&
1307
	    (ACCESS_ONCE(rnp->qsmask) & rdp->grpmask)) {
1308 1309 1310 1311

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

1312 1313
	} else if (rcu_gp_in_progress(rsp) &&
		   ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY)) {
1314

1315
		/* They had a few time units to dump stack, so complain. */
1316
		print_other_cpu_stall(rsp, gpnum);
1317 1318 1319
	}
}

1320 1321 1322 1323 1324 1325 1326 1327 1328 1329 1330
/**
 * 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)
{
1331 1332 1333
	struct rcu_state *rsp;

	for_each_rcu_flavor(rsp)
1334
		ACCESS_ONCE(rsp->jiffies_stall) = jiffies + ULONG_MAX / 2;
1335 1336
}

1337 1338 1339 1340 1341 1342 1343
/*
 * Initialize the specified rcu_data structure's callback list to empty.
 */
static void init_callback_list(struct rcu_data *rdp)
{
	int i;

1344 1345
	if (init_nocb_callback_list(rdp))
		return;
1346 1347 1348 1349 1350
	rdp->nxtlist = NULL;
	for (i = 0; i < RCU_NEXT_SIZE; i++)
		rdp->nxttail[i] = &rdp->nxtlist;
}

1351 1352 1353 1354 1355 1356 1357 1358 1359 1360 1361 1362 1363 1364 1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379
/*
 * 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;
}

1380 1381 1382 1383 1384
/*
 * 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,
1385
				unsigned long c, const char *s)
1386 1387 1388 1389 1390 1391 1392 1393 1394
{
	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
1395 1396
 * rcu_node structure's ->need_future_gp field.  Returns true if there
 * is reason to awaken the grace-period kthread.
1397 1398 1399
 *
 * The caller must hold the specified rcu_node structure's ->lock.
 */
1400 1401 1402
static bool __maybe_unused
rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
		    unsigned long *c_out)
1403 1404 1405
{
	unsigned long c;
	int i;
1406
	bool ret = false;
1407 1408 1409 1410 1411 1412 1413
	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);
1414
	trace_rcu_future_gp(rnp, rdp, c, TPS("Startleaf"));
1415
	if (rnp->need_future_gp[c & 0x1]) {
1416
		trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartleaf"));
1417
		goto out;
1418 1419 1420 1421 1422 1423 1424
	}

	/*
	 * 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
1425 1426 1427 1428 1429 1430 1431
	 * 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.
1432 1433
	 */
	if (rnp->gpnum != rnp->completed ||
1434
	    ACCESS_ONCE(rnp_root->gpnum) != ACCESS_ONCE(rnp_root->completed)) {
1435
		rnp->need_future_gp[c & 0x1]++;
1436
		trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleaf"));
1437
		goto out;
1438 1439 1440 1441 1442 1443 1444
	}

	/*
	 * 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).
	 */
1445
	if (rnp != rnp_root) {
1446
		raw_spin_lock(&rnp_root->lock);
1447 1448
		smp_mb__after_unlock_lock();
	}
1449 1450 1451 1452 1453 1454 1455 1456 1457 1458 1459 1460 1461 1462 1463 1464 1465

	/*
	 * 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]) {
1466
		trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartedroot"));
1467 1468 1469 1470 1471 1472 1473 1474
		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) {
1475
		trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleafroot"));
1476
	} else {
1477
		trace_rcu_future_gp(rnp, rdp, c, TPS("Startedroot"));
1478
		ret = rcu_start_gp_advanced(rdp->rsp, rnp_root, rdp);
1479 1480 1481 1482
	}
unlock_out:
	if (rnp != rnp_root)
		raw_spin_unlock(&rnp_root->lock);
1483 1484 1485 1486
out:
	if (c_out != NULL)
		*c_out = c;
	return ret;
1487 1488 1489 1490 1491 1492 1493 1494 1495 1496 1497 1498 1499 1500 1501 1502 1503
}

/*
 * 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];
1504 1505
	trace_rcu_future_gp(rnp, rdp, c,
			    needmore ? TPS("CleanupMore") : TPS("Cleanup"));
1506 1507 1508
	return needmore;
}

1509 1510 1511 1512 1513 1514 1515 1516 1517 1518 1519 1520 1521 1522 1523 1524
/*
 * 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 ||
	    !ACCESS_ONCE(rsp->gp_flags) ||
	    !rsp->gp_kthread)
		return;
	wake_up(&rsp->gp_wq);
}

1525 1526 1527 1528 1529 1530 1531
/*
 * 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
1532 1533
 * not hurt to call it repeatedly.  Returns an flag saying that we should
 * awaken the RCU grace-period kthread.
1534 1535 1536
 *
 * The caller must hold rnp->lock with interrupts disabled.
 */
1537
static bool rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
1538 1539 1540 1541
			       struct rcu_data *rdp)
{
	unsigned long c;
	int i;
1542
	bool ret;
1543 1544 1545

	/* If the CPU has no callbacks, nothing to do. */
	if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL])
1546
		return false;
1547 1548 1549 1550 1551 1552 1553 1554 1555 1556 1557 1558 1559 1560 1561 1562 1563 1564 1565 1566 1567 1568 1569 1570 1571 1572 1573 1574

	/*
	 * 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)
1575
		return false;
1576 1577 1578 1579 1580 1581 1582 1583 1584 1585

	/*
	 * 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;
	}
1586
	/* Record any needed additional grace periods. */
1587
	ret = rcu_start_future_gp(rnp, rdp, NULL);
1588 1589 1590

	/* Trace depending on how much we were able to accelerate. */
	if (!*rdp->nxttail[RCU_WAIT_TAIL])
1591
		trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccWaitCB"));
1592
	else
1593
		trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccReadyCB"));
1594
	return ret;
1595 1596 1597 1598 1599 1600 1601 1602
}

/*
 * 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...
1603
 * Returns true if the RCU grace-period kthread needs to be awakened.
1604 1605 1606
 *
 * The caller must hold rnp->lock with interrupts disabled.
 */
1607
static bool rcu_advance_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
1608 1609 1610 1611 1612 1613
			    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])
1614
		return false;
1615 1616 1617 1618 1619 1620 1621 1622 1623 1624 1625 1626 1627 1628 1629 1630 1631 1632 1633 1634 1635 1636 1637

	/*
	 * 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. */
1638
	return rcu_accelerate_cbs(rsp, rnp, rdp);
1639 1640
}

1641
/*
1642 1643 1644
 * 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.
1645
 * Returns true if the grace-period kthread needs to be awakened.
1646
 */
1647 1648
static bool __note_gp_changes(struct rcu_state *rsp, struct rcu_node *rnp,
			      struct rcu_data *rdp)
1649
{
1650 1651
	bool ret;

1652
	/* Handle the ends of any preceding grace periods first. */
1653 1654
	if (rdp->completed == rnp->completed &&
	    !unlikely(ACCESS_ONCE(rdp->gpwrap))) {
1655

1656
		/* No grace period end, so just accelerate recent callbacks. */
1657
		ret = rcu_accelerate_cbs(rsp, rnp, rdp);
1658

1659 1660 1661
	} else {

		/* Advance callbacks. */
1662
		ret = rcu_advance_cbs(rsp, rnp, rdp);
1663 1664 1665

		/* Remember that we saw this grace-period completion. */
		rdp->completed = rnp->completed;
1666
		trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuend"));
1667
	}
1668

1669
	if (rdp->gpnum != rnp->gpnum || unlikely(ACCESS_ONCE(rdp->gpwrap))) {
1670 1671 1672 1673 1674 1675
		/*
		 * 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;
1676
		trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpustart"));
1677
		rdp->passed_quiesce = 0;
1678
		rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_qs_ctr);
1679 1680
		rdp->qs_pending = !!(rnp->qsmask & rdp->grpmask);
		zero_cpu_stall_ticks(rdp);
1681
		ACCESS_ONCE(rdp->gpwrap) = false;
1682
	}
1683
	return ret;
1684 1685
}

1686
static void note_gp_changes(struct rcu_state *rsp, struct rcu_data *rdp)
1687 1688
{
	unsigned long flags;
1689
	bool needwake;
1690 1691 1692 1693
	struct rcu_node *rnp;

	local_irq_save(flags);
	rnp = rdp->mynode;
1694
	if ((rdp->gpnum == ACCESS_ONCE(rnp->gpnum) &&
1695 1696
	     rdp->completed == ACCESS_ONCE(rnp->completed) &&
	     !unlikely(ACCESS_ONCE(rdp->gpwrap))) || /* w/out lock. */
1697 1698 1699 1700
	    !raw_spin_trylock(&rnp->lock)) { /* irqs already off, so later. */
		local_irq_restore(flags);
		return;
	}
1701
	smp_mb__after_unlock_lock();
1702
	needwake = __note_gp_changes(rsp, rnp, rdp);
1703
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
1704 1705
	if (needwake)
		rcu_gp_kthread_wake(rsp);
1706 1707
}

1708
/*
1709
 * Initialize a new grace period.  Return 0 if no grace period required.
1710
 */
1711
static int rcu_gp_init(struct rcu_state *rsp)
1712 1713
{
	struct rcu_data *rdp;
1714
	struct rcu_node *rnp = rcu_get_root(rsp);
1715

1716
	ACCESS_ONCE(rsp->gp_activity) = jiffies;
1717
	rcu_bind_gp_kthread();
1718
	raw_spin_lock_irq(&rnp->lock);
1719
	smp_mb__after_unlock_lock();
1720
	if (!ACCESS_ONCE(rsp->gp_flags)) {
1721 1722 1723 1724
		/* Spurious wakeup, tell caller to go back to sleep.  */
		raw_spin_unlock_irq(&rnp->lock);
		return 0;
	}
1725
	ACCESS_ONCE(rsp->gp_flags) = 0; /* Clear all flags: New grace period. */
1726

1727 1728 1729 1730 1731
	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.
		 */
1732 1733 1734 1735 1736
		raw_spin_unlock_irq(&rnp->lock);
		return 0;
	}

	/* Advance to a new grace period and initialize state. */
1737
	record_gp_stall_check_time(rsp);
1738 1739
	/* Record GP times before starting GP, hence smp_store_release(). */
	smp_store_release(&rsp->gpnum, rsp->gpnum + 1);
1740
	trace_rcu_grace_period(rsp->name, rsp->gpnum, TPS("start"));
1741 1742 1743
	raw_spin_unlock_irq(&rnp->lock);

	/* Exclude any concurrent CPU-hotplug operations. */
1744
	mutex_lock(&rsp->onoff_mutex);
1745
	smp_mb__after_unlock_lock(); /* ->gpnum increment before GP! */
1746 1747 1748 1749 1750 1751 1752 1753 1754 1755 1756 1757 1758 1759 1760

	/*
	 * 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) {
1761
		raw_spin_lock_irq(&rnp->lock);
1762
		smp_mb__after_unlock_lock();
1763
		rdp = this_cpu_ptr(rsp->rda);
1764 1765
		rcu_preempt_check_blocked_tasks(rnp);
		rnp->qsmask = rnp->qsmaskinit;
1766
		ACCESS_ONCE(rnp->gpnum) = rsp->gpnum;
1767
		WARN_ON_ONCE(rnp->completed != rsp->completed);
1768
		ACCESS_ONCE(rnp->completed) = rsp->completed;
1769
		if (rnp == rdp->mynode)
1770
			(void)__note_gp_changes(rsp, rnp, rdp);
1771 1772 1773 1774 1775
		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);
1776
		cond_resched_rcu_qs();
1777
		ACCESS_ONCE(rsp->gp_activity) = jiffies;
1778 1779 1780 1781
		if (IS_ENABLED(CONFIG_RCU_TORTURE_TEST_SLOW_INIT) &&
		    gp_init_delay > 0 &&
		    !(rsp->gpnum % (rcu_num_nodes * 10)))
			schedule_timeout_uninterruptible(gp_init_delay);
1782
	}
1783

1784
	mutex_unlock(&rsp->onoff_mutex);
1785 1786
	return 1;
}
1787

1788 1789 1790
/*
 * Do one round of quiescent-state forcing.
 */
1791
static int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in)
1792 1793
{
	int fqs_state = fqs_state_in;
1794 1795
	bool isidle = false;
	unsigned long maxj;
1796 1797
	struct rcu_node *rnp = rcu_get_root(rsp);

1798
	ACCESS_ONCE(rsp->gp_activity) = jiffies;
1799 1800 1801
	rsp->n_force_qs++;
	if (fqs_state == RCU_SAVE_DYNTICK) {
		/* Collect dyntick-idle snapshots. */
1802
		if (is_sysidle_rcu_state(rsp)) {
1803
			isidle = true;
1804 1805
			maxj = jiffies - ULONG_MAX / 4;
		}
1806 1807
		force_qs_rnp(rsp, dyntick_save_progress_counter,
			     &isidle, &maxj);
1808
		rcu_sysidle_report_gp(rsp, isidle, maxj);
1809 1810 1811
		fqs_state = RCU_FORCE_QS;
	} else {
		/* Handle dyntick-idle and offline CPUs. */
1812
		isidle = false;
1813
		force_qs_rnp(rsp, rcu_implicit_dynticks_qs, &isidle, &maxj);
1814 1815 1816 1817
	}
	/* Clear flag to prevent immediate re-entry. */
	if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
		raw_spin_lock_irq(&rnp->lock);
1818
		smp_mb__after_unlock_lock();
1819 1820
		ACCESS_ONCE(rsp->gp_flags) =
			ACCESS_ONCE(rsp->gp_flags) & ~RCU_GP_FLAG_FQS;
1821 1822 1823 1824 1825
		raw_spin_unlock_irq(&rnp->lock);
	}
	return fqs_state;
}

1826 1827 1828
/*
 * Clean up after the old grace period.
 */
1829
static void rcu_gp_cleanup(struct rcu_state *rsp)
1830 1831
{
	unsigned long gp_duration;
1832
	bool needgp = false;
1833
	int nocb = 0;
1834 1835
	struct rcu_data *rdp;
	struct rcu_node *rnp = rcu_get_root(rsp);
1836

1837
	ACCESS_ONCE(rsp->gp_activity) = jiffies;
1838
	raw_spin_lock_irq(&rnp->lock);
1839
	smp_mb__after_unlock_lock();
1840 1841 1842
	gp_duration = jiffies - rsp->gp_start;
	if (gp_duration > rsp->gp_max)
		rsp->gp_max = gp_duration;
1843

1844 1845 1846 1847 1848 1849 1850 1851
	/*
	 * 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.
	 */
1852
	raw_spin_unlock_irq(&rnp->lock);
1853

1854 1855 1856 1857 1858 1859 1860 1861 1862 1863
	/*
	 * 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) {
1864
		raw_spin_lock_irq(&rnp->lock);
1865
		smp_mb__after_unlock_lock();
1866
		ACCESS_ONCE(rnp->completed) = rsp->gpnum;
1867 1868
		rdp = this_cpu_ptr(rsp->rda);
		if (rnp == rdp->mynode)
1869
			needgp = __note_gp_changes(rsp, rnp, rdp) || needgp;
1870
		/* smp_mb() provided by prior unlock-lock pair. */
1871
		nocb += rcu_future_gp_cleanup(rsp, rnp);
1872
		raw_spin_unlock_irq(&rnp->lock);
1873
		cond_resched_rcu_qs();
1874
		ACCESS_ONCE(rsp->gp_activity) = jiffies;
1875
	}
1876 1877
	rnp = rcu_get_root(rsp);
	raw_spin_lock_irq(&rnp->lock);
1878
	smp_mb__after_unlock_lock(); /* Order GP before ->completed update. */
1879
	rcu_nocb_gp_set(rnp, nocb);
1880

1881 1882
	/* Declare grace period done. */
	ACCESS_ONCE(rsp->completed) = rsp->gpnum;
1883
	trace_rcu_grace_period(rsp->name, rsp->completed, TPS("end"));
1884
	rsp->fqs_state = RCU_GP_IDLE;
1885
	rdp = this_cpu_ptr(rsp->rda);
1886 1887 1888
	/* Advance CBs to reduce false positives below. */
	needgp = rcu_advance_cbs(rsp, rnp, rdp) || needgp;
	if (needgp || cpu_needs_another_gp(rsp, rdp)) {
1889
		ACCESS_ONCE(rsp->gp_flags) = RCU_GP_FLAG_INIT;
1890 1891 1892 1893
		trace_rcu_grace_period(rsp->name,
				       ACCESS_ONCE(rsp->gpnum),
				       TPS("newreq"));
	}
1894 1895 1896 1897 1898 1899 1900 1901
	raw_spin_unlock_irq(&rnp->lock);
}

/*
 * Body of kthread that handles grace periods.
 */
static int __noreturn rcu_gp_kthread(void *arg)
{
1902
	int fqs_state;
1903
	int gf;
1904
	unsigned long j;
1905
	int ret;
1906 1907 1908 1909 1910 1911 1912
	struct rcu_state *rsp = arg;
	struct rcu_node *rnp = rcu_get_root(rsp);

	for (;;) {

		/* Handle grace-period start. */
		for (;;) {
1913 1914 1915
			trace_rcu_grace_period(rsp->name,
					       ACCESS_ONCE(rsp->gpnum),
					       TPS("reqwait"));
1916
			rsp->gp_state = RCU_GP_WAIT_GPS;
1917
			wait_event_interruptible(rsp->gp_wq,
1918
						 ACCESS_ONCE(rsp->gp_flags) &
1919
						 RCU_GP_FLAG_INIT);
1920
			/* Locking provides needed memory barrier. */
1921
			if (rcu_gp_init(rsp))
1922
				break;
1923
			cond_resched_rcu_qs();
1924
			ACCESS_ONCE(rsp->gp_activity) = jiffies;
1925
			WARN_ON(signal_pending(current));
1926 1927 1928
			trace_rcu_grace_period(rsp->name,
					       ACCESS_ONCE(rsp->gpnum),
					       TPS("reqwaitsig"));
1929
		}
1930

1931 1932
		/* Handle quiescent-state forcing. */
		fqs_state = RCU_SAVE_DYNTICK;
1933 1934 1935 1936 1937
		j = jiffies_till_first_fqs;
		if (j > HZ) {
			j = HZ;
			jiffies_till_first_fqs = HZ;
		}
1938
		ret = 0;
1939
		for (;;) {
1940 1941
			if (!ret)
				rsp->jiffies_force_qs = jiffies + j;
1942 1943 1944
			trace_rcu_grace_period(rsp->name,
					       ACCESS_ONCE(rsp->gpnum),
					       TPS("fqswait"));
1945
			rsp->gp_state = RCU_GP_WAIT_FQS;
1946
			ret = wait_event_interruptible_timeout(rsp->gp_wq,
1947 1948
					((gf = ACCESS_ONCE(rsp->gp_flags)) &
					 RCU_GP_FLAG_FQS) ||
1949 1950
					(!ACCESS_ONCE(rnp->qsmask) &&
					 !rcu_preempt_blocked_readers_cgp(rnp)),
1951
					j);
1952
			/* Locking provides needed memory barriers. */
1953
			/* If grace period done, leave loop. */
1954
			if (!ACCESS_ONCE(rnp->qsmask) &&
1955
			    !rcu_preempt_blocked_readers_cgp(rnp))
1956
				break;
1957
			/* If time for quiescent-state forcing, do it. */
1958 1959
			if (ULONG_CMP_GE(jiffies, rsp->jiffies_force_qs) ||
			    (gf & RCU_GP_FLAG_FQS)) {
1960 1961 1962
				trace_rcu_grace_period(rsp->name,
						       ACCESS_ONCE(rsp->gpnum),
						       TPS("fqsstart"));
1963
				fqs_state = rcu_gp_fqs(rsp, fqs_state);
1964 1965 1966
				trace_rcu_grace_period(rsp->name,
						       ACCESS_ONCE(rsp->gpnum),
						       TPS("fqsend"));
1967
				cond_resched_rcu_qs();
1968
				ACCESS_ONCE(rsp->gp_activity) = jiffies;
1969 1970
			} else {
				/* Deal with stray signal. */
1971
				cond_resched_rcu_qs();
1972
				ACCESS_ONCE(rsp->gp_activity) = jiffies;
1973
				WARN_ON(signal_pending(current));
1974 1975 1976
				trace_rcu_grace_period(rsp->name,
						       ACCESS_ONCE(rsp->gpnum),
						       TPS("fqswaitsig"));
1977
			}
1978 1979 1980 1981 1982 1983 1984 1985
			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;
			}
1986
		}
1987 1988 1989

		/* Handle grace-period end. */
		rcu_gp_cleanup(rsp);
1990 1991 1992
	}
}

1993 1994 1995
/*
 * Start a new RCU grace period if warranted, re-initializing the hierarchy
 * in preparation for detecting the next grace period.  The caller must hold
1996
 * the root node's ->lock and hard irqs must be disabled.
1997 1998 1999 2000
 *
 * 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.
2001 2002
 *
 * Returns true if the grace-period kthread must be awakened.
2003
 */
2004
static bool
2005 2006
rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
		      struct rcu_data *rdp)
2007
{
2008
	if (!rsp->gp_kthread || !cpu_needs_another_gp(rsp, rdp)) {
2009
		/*
2010
		 * Either we have not yet spawned the grace-period
2011 2012
		 * task, this CPU does not need another grace period,
		 * or a grace period is already in progress.
2013
		 * Either way, don't start a new grace period.
2014
		 */
2015
		return false;
2016
	}
2017
	ACCESS_ONCE(rsp->gp_flags) = RCU_GP_FLAG_INIT;
2018 2019
	trace_rcu_grace_period(rsp->name, ACCESS_ONCE(rsp->gpnum),
			       TPS("newreq"));
2020

2021 2022
	/*
	 * We can't do wakeups while holding the rnp->lock, as that
2023
	 * could cause possible deadlocks with the rq->lock. Defer
2024
	 * the wakeup to our caller.
2025
	 */
2026
	return true;
2027 2028
}

2029 2030 2031 2032 2033 2034
/*
 * 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.
2035 2036
 *
 * Returns true if the grace-period kthread needs to be awakened.
2037
 */
2038
static bool rcu_start_gp(struct rcu_state *rsp)
2039 2040 2041
{
	struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
	struct rcu_node *rnp = rcu_get_root(rsp);
2042
	bool ret = false;
2043 2044 2045 2046 2047 2048 2049 2050 2051

	/*
	 * 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!
	 */
2052 2053 2054
	ret = rcu_advance_cbs(rsp, rnp, rdp) || ret;
	ret = rcu_start_gp_advanced(rsp, rnp, rdp) || ret;
	return ret;
2055 2056
}

2057
/*
P
Paul E. McKenney 已提交
2058 2059 2060
 * 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
2061 2062
 * if one is needed.  Note that the caller must hold rnp->lock, which
 * is released before return.
2063
 */
P
Paul E. McKenney 已提交
2064
static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
2065
	__releases(rcu_get_root(rsp)->lock)
2066
{
2067
	WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
2068
	raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags);
2069
	rcu_gp_kthread_wake(rsp);
2070 2071
}

2072
/*
P
Paul E. McKenney 已提交
2073 2074 2075 2076 2077 2078
 * 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
 * must be represented by the same rcu_node structure (which need not be
 * a leaf rcu_node structure, though it often will be).  That structure's
 * lock must be held upon entry, and it is released before return.
2079 2080
 */
static void
P
Paul E. McKenney 已提交
2081 2082
rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
		  struct rcu_node *rnp, unsigned long flags)
2083 2084
	__releases(rnp->lock)
{
2085 2086
	struct rcu_node *rnp_c;

2087 2088 2089 2090 2091
	/* Walk up the rcu_node hierarchy. */
	for (;;) {
		if (!(rnp->qsmask & mask)) {

			/* Our bit has already been cleared, so done. */
P
Paul E. McKenney 已提交
2092
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
2093 2094 2095
			return;
		}
		rnp->qsmask &= ~mask;
2096 2097 2098 2099
		trace_rcu_quiescent_state_report(rsp->name, rnp->gpnum,
						 mask, rnp->qsmask, rnp->level,
						 rnp->grplo, rnp->grphi,
						 !!rnp->gp_tasks);
2100
		if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
2101 2102

			/* Other bits still set at this level, so done. */
P
Paul E. McKenney 已提交
2103
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
2104 2105 2106 2107 2108 2109 2110 2111 2112
			return;
		}
		mask = rnp->grpmask;
		if (rnp->parent == NULL) {

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

			break;
		}
P
Paul E. McKenney 已提交
2113
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
2114
		rnp_c = rnp;
2115
		rnp = rnp->parent;
P
Paul E. McKenney 已提交
2116
		raw_spin_lock_irqsave(&rnp->lock, flags);
2117
		smp_mb__after_unlock_lock();
2118
		WARN_ON_ONCE(rnp_c->qsmask);
2119 2120 2121 2122
	}

	/*
	 * Get here if we are the last CPU to pass through a quiescent
P
Paul E. McKenney 已提交
2123
	 * state for this grace period.  Invoke rcu_report_qs_rsp()
2124
	 * to clean up and start the next grace period if one is needed.
2125
	 */
P
Paul E. McKenney 已提交
2126
	rcu_report_qs_rsp(rsp, flags); /* releases rnp->lock. */
2127 2128
}

2129 2130 2131 2132 2133 2134 2135 2136 2137 2138 2139 2140 2141 2142 2143 2144 2145 2146 2147 2148 2149 2150 2151 2152 2153 2154 2155 2156 2157 2158 2159 2160 2161 2162 2163 2164 2165 2166 2167
/*
 * 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.
 */
static void __maybe_unused rcu_report_unblock_qs_rnp(struct rcu_state *rsp,
				      struct rcu_node *rnp, unsigned long flags)
	__releases(rnp->lock)
{
	unsigned long mask;
	struct rcu_node *rnp_p;

	WARN_ON_ONCE(rsp == &rcu_bh_state || rsp == &rcu_sched_state);
	if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
		return;  /* Still need more quiescent states! */
	}

	rnp_p = rnp->parent;
	if (rnp_p == NULL) {
		/*
		 * Either there is only one rcu_node in the tree,
		 * or tasks were kicked up to root rcu_node due to
		 * CPUs going offline.
		 */
		rcu_report_qs_rsp(rsp, flags);
		return;
	}

	/* Report up the rest of the hierarchy. */
	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();
	rcu_report_qs_rnp(mask, rsp, rnp_p, flags);
}

2168
/*
P
Paul E. McKenney 已提交
2169 2170 2171 2172 2173 2174 2175
 * 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!
2176 2177
 */
static void
2178
rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp)
2179 2180 2181
{
	unsigned long flags;
	unsigned long mask;
2182
	bool needwake;
2183 2184 2185
	struct rcu_node *rnp;

	rnp = rdp->mynode;
P
Paul E. McKenney 已提交
2186
	raw_spin_lock_irqsave(&rnp->lock, flags);
2187
	smp_mb__after_unlock_lock();
2188 2189 2190 2191
	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) {
2192 2193

		/*
2194 2195 2196 2197
		 * 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.
2198
		 */
2199
		rdp->passed_quiesce = 0;	/* need qs for new gp. */
2200
		rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_qs_ctr);
P
Paul E. McKenney 已提交
2201
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
2202 2203 2204 2205
		return;
	}
	mask = rdp->grpmask;
	if ((rnp->qsmask & mask) == 0) {
P
Paul E. McKenney 已提交
2206
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
2207 2208 2209 2210 2211 2212 2213
	} 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.
		 */
2214
		needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
2215

P
Paul E. McKenney 已提交
2216
		rcu_report_qs_rnp(mask, rsp, rnp, flags); /* rlses rnp->lock */
2217 2218
		if (needwake)
			rcu_gp_kthread_wake(rsp);
2219 2220 2221 2222 2223 2224 2225 2226 2227 2228 2229 2230
	}
}

/*
 * 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)
{
2231 2232
	/* Check for grace-period ends and beginnings. */
	note_gp_changes(rsp, rdp);
2233 2234 2235 2236 2237 2238 2239 2240 2241 2242 2243 2244

	/*
	 * 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.
	 */
2245 2246
	if (!rdp->passed_quiesce &&
	    rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_qs_ctr))
2247 2248
		return;

P
Paul E. McKenney 已提交
2249 2250 2251 2252
	/*
	 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
	 * judge of that).
	 */
2253
	rcu_report_qs_rdp(rdp->cpu, rsp, rdp);
2254 2255 2256 2257
}

#ifdef CONFIG_HOTPLUG_CPU

2258
/*
2259 2260
 * Send the specified CPU's RCU callbacks to the orphanage.  The
 * specified CPU must be offline, and the caller must hold the
2261
 * ->orphan_lock.
2262
 */
2263 2264 2265
static void
rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
			  struct rcu_node *rnp, struct rcu_data *rdp)
2266
{
P
Paul E. McKenney 已提交
2267
	/* No-CBs CPUs do not have orphanable callbacks. */
2268
	if (rcu_is_nocb_cpu(rdp->cpu))
P
Paul E. McKenney 已提交
2269 2270
		return;

2271 2272
	/*
	 * Orphan the callbacks.  First adjust the counts.  This is safe
2273 2274
	 * because _rcu_barrier() excludes CPU-hotplug operations, so it
	 * cannot be running now.  Thus no memory barrier is required.
2275
	 */
2276
	if (rdp->nxtlist != NULL) {
2277 2278 2279
		rsp->qlen_lazy += rdp->qlen_lazy;
		rsp->qlen += rdp->qlen;
		rdp->n_cbs_orphaned += rdp->qlen;
2280
		rdp->qlen_lazy = 0;
2281
		ACCESS_ONCE(rdp->qlen) = 0;
2282 2283 2284
	}

	/*
2285 2286 2287 2288 2289 2290 2291
	 * 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.
2292
	 */
2293 2294 2295 2296
	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;
2297 2298 2299
	}

	/*
2300 2301 2302
	 * 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.
2303
	 */
2304
	if (rdp->nxtlist != NULL) {
2305 2306
		*rsp->orphan_donetail = rdp->nxtlist;
		rsp->orphan_donetail = rdp->nxttail[RCU_DONE_TAIL];
2307
	}
2308

2309 2310 2311 2312
	/*
	 * Finally, initialize the rcu_data structure's list to empty and
	 * disallow further callbacks on this CPU.
	 */
2313
	init_callback_list(rdp);
2314
	rdp->nxttail[RCU_NEXT_TAIL] = NULL;
2315 2316 2317 2318
}

/*
 * Adopt the RCU callbacks from the specified rcu_state structure's
2319
 * orphanage.  The caller must hold the ->orphan_lock.
2320
 */
2321
static void rcu_adopt_orphan_cbs(struct rcu_state *rsp, unsigned long flags)
2322 2323
{
	int i;
2324
	struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
2325

P
Paul E. McKenney 已提交
2326
	/* No-CBs CPUs are handled specially. */
2327
	if (rcu_nocb_adopt_orphan_cbs(rsp, rdp, flags))
P
Paul E. McKenney 已提交
2328 2329
		return;

2330 2331 2332 2333
	/* Do the accounting first. */
	rdp->qlen_lazy += rsp->qlen_lazy;
	rdp->qlen += rsp->qlen;
	rdp->n_cbs_adopted += rsp->qlen;
2334 2335
	if (rsp->qlen_lazy != rsp->qlen)
		rcu_idle_count_callbacks_posted();
2336 2337 2338 2339 2340 2341 2342 2343 2344 2345 2346 2347 2348 2349 2350 2351 2352 2353 2354 2355 2356 2357 2358 2359 2360 2361 2362 2363 2364 2365 2366 2367 2368 2369 2370 2371 2372 2373 2374
	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);
2375 2376
	trace_rcu_grace_period(rsp->name,
			       rnp->gpnum + 1 - !!(rnp->qsmask & mask),
2377
			       TPS("cpuofl"));
2378 2379
}

2380 2381 2382 2383 2384 2385 2386 2387 2388 2389 2390 2391 2392 2393 2394 2395 2396 2397 2398 2399 2400 2401 2402 2403 2404 2405 2406 2407 2408 2409 2410 2411 2412 2413 2414 2415 2416 2417 2418 2419
/*
 * 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;
		if (rnp->qsmaskinit) {
			raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
			return;
		}
		raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
	}
}

2420
/*
2421
 * The CPU has been completely removed, and some other CPU is reporting
2422 2423
 * this fact from process context.  Do the remainder of the cleanup,
 * including orphaning the outgoing CPU's RCU callbacks, and also
2424 2425
 * 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.
2426
 */
2427
static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
2428
{
2429
	unsigned long flags;
2430
	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
2431
	struct rcu_node *rnp = rdp->mynode;  /* Outgoing CPU's rdp & rnp. */
2432

2433
	/* Adjust any no-longer-needed kthreads. */
T
Thomas Gleixner 已提交
2434
	rcu_boost_kthread_setaffinity(rnp, -1);
2435 2436

	/* Exclude any attempts to start a new grace period. */
2437
	mutex_lock(&rsp->onoff_mutex);
2438

2439
	/* Orphan the dead CPU's callbacks, and adopt them if appropriate. */
2440
	raw_spin_lock_irqsave(&rsp->orphan_lock, flags);
2441
	rcu_send_cbs_to_orphanage(cpu, rsp, rnp, rdp);
2442
	rcu_adopt_orphan_cbs(rsp, flags);
2443
	raw_spin_unlock_irqrestore(&rsp->orphan_lock, flags);
2444

2445
	/* Remove outgoing CPU from mask in the leaf rcu_node structure. */
2446
	raw_spin_lock_irqsave(&rnp->lock, flags);
2447 2448
	smp_mb__after_unlock_lock();	/* Enforce GP memory-order guarantee. */
	rnp->qsmaskinit &= ~rdp->grpmask;
2449
	if (rnp->qsmaskinit == 0 && !rcu_preempt_has_tasks(rnp))
2450
		rcu_cleanup_dead_rnp(rnp);
2451
	rcu_report_qs_rnp(rdp->grpmask, rsp, rnp, flags); /* Rlses rnp->lock. */
2452 2453 2454
	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);
2455
	mutex_unlock(&rsp->onoff_mutex);
2456 2457 2458 2459
}

#else /* #ifdef CONFIG_HOTPLUG_CPU */

2460
static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
2461 2462 2463
{
}

2464 2465 2466 2467
static void __maybe_unused rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf)
{
}

2468
static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
2469 2470 2471 2472 2473 2474 2475 2476 2477
{
}

#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.
 */
2478
static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
2479 2480 2481
{
	unsigned long flags;
	struct rcu_head *next, *list, **tail;
E
Eric Dumazet 已提交
2482 2483
	long bl, count, count_lazy;
	int i;
2484

2485
	/* If no callbacks are ready, just return. */
2486
	if (!cpu_has_callbacks_ready_to_invoke(rdp)) {
2487
		trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, 0);
2488 2489 2490
		trace_rcu_batch_end(rsp->name, 0, !!ACCESS_ONCE(rdp->nxtlist),
				    need_resched(), is_idle_task(current),
				    rcu_is_callbacks_kthread());
2491
		return;
2492
	}
2493 2494 2495 2496 2497 2498

	/*
	 * Extract the list of ready callbacks, disabling to prevent
	 * races with call_rcu() from interrupt handlers.
	 */
	local_irq_save(flags);
2499
	WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
2500
	bl = rdp->blimit;
2501
	trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, bl);
2502 2503 2504 2505
	list = rdp->nxtlist;
	rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
	*rdp->nxttail[RCU_DONE_TAIL] = NULL;
	tail = rdp->nxttail[RCU_DONE_TAIL];
2506 2507 2508
	for (i = RCU_NEXT_SIZE - 1; i >= 0; i--)
		if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
			rdp->nxttail[i] = &rdp->nxtlist;
2509 2510 2511
	local_irq_restore(flags);

	/* Invoke callbacks. */
2512
	count = count_lazy = 0;
2513 2514 2515
	while (list) {
		next = list->next;
		prefetch(next);
2516
		debug_rcu_head_unqueue(list);
2517 2518
		if (__rcu_reclaim(rsp->name, list))
			count_lazy++;
2519
		list = next;
2520 2521 2522 2523
		/* Stop only if limit reached and CPU has something to do. */
		if (++count >= bl &&
		    (need_resched() ||
		     (!is_idle_task(current) && !rcu_is_callbacks_kthread())))
2524 2525 2526 2527
			break;
	}

	local_irq_save(flags);
2528 2529 2530
	trace_rcu_batch_end(rsp->name, count, !!list, need_resched(),
			    is_idle_task(current),
			    rcu_is_callbacks_kthread());
2531 2532 2533 2534 2535

	/* Update count, and requeue any remaining callbacks. */
	if (list != NULL) {
		*tail = rdp->nxtlist;
		rdp->nxtlist = list;
2536 2537 2538
		for (i = 0; i < RCU_NEXT_SIZE; i++)
			if (&rdp->nxtlist == rdp->nxttail[i])
				rdp->nxttail[i] = tail;
2539 2540 2541
			else
				break;
	}
2542 2543
	smp_mb(); /* List handling before counting for rcu_barrier(). */
	rdp->qlen_lazy -= count_lazy;
2544
	ACCESS_ONCE(rdp->qlen) = rdp->qlen - count;
2545
	rdp->n_cbs_invoked += count;
2546 2547 2548 2549 2550

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

2551 2552 2553 2554 2555 2556
	/* 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;
2557
	WARN_ON_ONCE((rdp->nxtlist == NULL) != (rdp->qlen == 0));
2558

2559 2560
	local_irq_restore(flags);

2561
	/* Re-invoke RCU core processing if there are callbacks remaining. */
2562
	if (cpu_has_callbacks_ready_to_invoke(rdp))
2563
		invoke_rcu_core();
2564 2565 2566 2567 2568
}

/*
 * 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).
2569
 * Also schedule RCU core processing.
2570
 *
2571
 * This function must be called from hardirq context.  It is normally
2572 2573 2574
 * invoked from the scheduling-clock interrupt.  If rcu_pending returns
 * false, there is no point in invoking rcu_check_callbacks().
 */
2575
void rcu_check_callbacks(int user)
2576
{
2577
	trace_rcu_utilization(TPS("Start scheduler-tick"));
2578
	increment_cpu_stall_ticks();
2579
	if (user || rcu_is_cpu_rrupt_from_idle()) {
2580 2581 2582 2583 2584

		/*
		 * 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
2585
		 * a quiescent state, so note it.
2586 2587
		 *
		 * No memory barrier is required here because both
2588 2589 2590
		 * 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.
2591 2592
		 */

2593 2594
		rcu_sched_qs();
		rcu_bh_qs();
2595 2596 2597 2598 2599 2600 2601

	} 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
2602
		 * critical section, so note it.
2603 2604
		 */

2605
		rcu_bh_qs();
2606
	}
2607
	rcu_preempt_check_callbacks();
2608
	if (rcu_pending())
2609
		invoke_rcu_core();
P
Paul E. McKenney 已提交
2610 2611
	if (user)
		rcu_note_voluntary_context_switch(current);
2612
	trace_rcu_utilization(TPS("End scheduler-tick"));
2613 2614 2615 2616 2617
}

/*
 * Scan the leaf rcu_node structures, processing dyntick state for any that
 * have not yet encountered a quiescent state, using the function specified.
2618 2619
 * Also initiate boosting for any threads blocked on the root rcu_node.
 *
2620
 * The caller must have suppressed start of new grace periods.
2621
 */
2622 2623 2624 2625
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)
2626 2627 2628 2629 2630
{
	unsigned long bit;
	int cpu;
	unsigned long flags;
	unsigned long mask;
2631
	struct rcu_node *rnp;
2632

2633
	rcu_for_each_leaf_node(rsp, rnp) {
2634
		cond_resched_rcu_qs();
2635
		mask = 0;
P
Paul E. McKenney 已提交
2636
		raw_spin_lock_irqsave(&rnp->lock, flags);
2637
		smp_mb__after_unlock_lock();
2638
		if (!rcu_gp_in_progress(rsp)) {
P
Paul E. McKenney 已提交
2639
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
2640
			return;
2641
		}
2642
		if (rnp->qsmask == 0) {
2643
			rcu_initiate_boost(rnp, flags); /* releases rnp->lock */
2644 2645
			continue;
		}
2646
		cpu = rnp->grplo;
2647
		bit = 1;
2648
		for (; cpu <= rnp->grphi; cpu++, bit <<= 1) {
2649 2650
			if ((rnp->qsmask & bit) != 0) {
				if ((rnp->qsmaskinit & bit) != 0)
2651
					*isidle = false;
2652 2653 2654
				if (f(per_cpu_ptr(rsp->rda, cpu), isidle, maxj))
					mask |= bit;
			}
2655
		}
2656
		if (mask != 0) {
2657

P
Paul E. McKenney 已提交
2658 2659
			/* rcu_report_qs_rnp() releases rnp->lock. */
			rcu_report_qs_rnp(mask, rsp, rnp, flags);
2660 2661
			continue;
		}
P
Paul E. McKenney 已提交
2662
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
2663 2664 2665 2666 2667 2668 2669
	}
}

/*
 * Force quiescent states on reluctant CPUs, and also detect which
 * CPUs are in dyntick-idle mode.
 */
2670
static void force_quiescent_state(struct rcu_state *rsp)
2671 2672
{
	unsigned long flags;
2673 2674 2675 2676 2677
	bool ret;
	struct rcu_node *rnp;
	struct rcu_node *rnp_old = NULL;

	/* Funnel through hierarchy to reduce memory contention. */
2678
	rnp = __this_cpu_read(rsp->rda->mynode);
2679 2680 2681 2682 2683 2684
	for (; rnp != NULL; rnp = rnp->parent) {
		ret = (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) ||
		      !raw_spin_trylock(&rnp->fqslock);
		if (rnp_old != NULL)
			raw_spin_unlock(&rnp_old->fqslock);
		if (ret) {
2685
			rsp->n_force_qs_lh++;
2686 2687 2688 2689 2690
			return;
		}
		rnp_old = rnp;
	}
	/* rnp_old == rcu_get_root(rsp), rnp == NULL. */
2691

2692 2693
	/* Reached the root of the rcu_node tree, acquire lock. */
	raw_spin_lock_irqsave(&rnp_old->lock, flags);
2694
	smp_mb__after_unlock_lock();
2695 2696
	raw_spin_unlock(&rnp_old->fqslock);
	if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
2697
		rsp->n_force_qs_lh++;
2698
		raw_spin_unlock_irqrestore(&rnp_old->lock, flags);
2699
		return;  /* Someone beat us to it. */
2700
	}
2701 2702
	ACCESS_ONCE(rsp->gp_flags) =
		ACCESS_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS;
2703
	raw_spin_unlock_irqrestore(&rnp_old->lock, flags);
2704
	rcu_gp_kthread_wake(rsp);
2705 2706 2707
}

/*
2708 2709 2710
 * 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.
2711 2712
 */
static void
2713
__rcu_process_callbacks(struct rcu_state *rsp)
2714 2715
{
	unsigned long flags;
2716
	bool needwake;
2717
	struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
2718

2719 2720
	WARN_ON_ONCE(rdp->beenonline == 0);

2721 2722 2723 2724
	/* 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? */
2725
	local_irq_save(flags);
2726
	if (cpu_needs_another_gp(rsp, rdp)) {
2727
		raw_spin_lock(&rcu_get_root(rsp)->lock); /* irqs disabled. */
2728
		needwake = rcu_start_gp(rsp);
2729
		raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags);
2730 2731
		if (needwake)
			rcu_gp_kthread_wake(rsp);
2732 2733
	} else {
		local_irq_restore(flags);
2734 2735 2736
	}

	/* If there are callbacks ready, invoke them. */
2737
	if (cpu_has_callbacks_ready_to_invoke(rdp))
2738
		invoke_rcu_callbacks(rsp, rdp);
2739 2740 2741

	/* Do any needed deferred wakeups of rcuo kthreads. */
	do_nocb_deferred_wakeup(rdp);
2742 2743
}

2744
/*
2745
 * Do RCU core processing for the current CPU.
2746
 */
2747
static void rcu_process_callbacks(struct softirq_action *unused)
2748
{
2749 2750
	struct rcu_state *rsp;

2751 2752
	if (cpu_is_offline(smp_processor_id()))
		return;
2753
	trace_rcu_utilization(TPS("Start RCU core"));
2754 2755
	for_each_rcu_flavor(rsp)
		__rcu_process_callbacks(rsp);
2756
	trace_rcu_utilization(TPS("End RCU core"));
2757 2758
}

2759
/*
2760 2761 2762
 * 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
2763
 * are running on the current CPU with softirqs disabled, the
2764
 * rcu_cpu_kthread_task cannot disappear out from under us.
2765
 */
2766
static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
2767
{
2768 2769
	if (unlikely(!ACCESS_ONCE(rcu_scheduler_fully_active)))
		return;
2770 2771
	if (likely(!rsp->boost)) {
		rcu_do_batch(rsp, rdp);
2772 2773
		return;
	}
2774
	invoke_rcu_callbacks_kthread();
2775 2776
}

2777
static void invoke_rcu_core(void)
2778
{
2779 2780
	if (cpu_online(smp_processor_id()))
		raise_softirq(RCU_SOFTIRQ);
2781 2782
}

2783 2784 2785 2786 2787
/*
 * 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)
2788
{
2789 2790
	bool needwake;

2791 2792 2793 2794
	/*
	 * If called from an extended quiescent state, invoke the RCU
	 * core in order to force a re-evaluation of RCU's idleness.
	 */
2795
	if (!rcu_is_watching() && cpu_online(smp_processor_id()))
2796 2797
		invoke_rcu_core();

2798
	/* If interrupts were disabled or CPU offline, don't invoke RCU core. */
2799
	if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
2800
		return;
2801

2802 2803 2804 2805 2806 2807 2808
	/*
	 * 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.
	 */
2809
	if (unlikely(rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) {
2810 2811

		/* Are we ignoring a completed grace period? */
2812
		note_gp_changes(rsp, rdp);
2813 2814 2815 2816 2817

		/* 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);

2818
			raw_spin_lock(&rnp_root->lock);
2819
			smp_mb__after_unlock_lock();
2820
			needwake = rcu_start_gp(rsp);
2821
			raw_spin_unlock(&rnp_root->lock);
2822 2823
			if (needwake)
				rcu_gp_kthread_wake(rsp);
2824 2825 2826 2827 2828
		} 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)
2829
				force_quiescent_state(rsp);
2830 2831 2832
			rdp->n_force_qs_snap = rsp->n_force_qs;
			rdp->qlen_last_fqs_check = rdp->qlen;
		}
2833
	}
2834 2835
}

2836 2837 2838 2839 2840 2841 2842
/*
 * RCU callback function to leak a callback.
 */
static void rcu_leak_callback(struct rcu_head *rhp)
{
}

P
Paul E. McKenney 已提交
2843 2844 2845 2846 2847 2848
/*
 * 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.
 */
2849 2850
static void
__call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
P
Paul E. McKenney 已提交
2851
	   struct rcu_state *rsp, int cpu, bool lazy)
2852 2853 2854 2855
{
	unsigned long flags;
	struct rcu_data *rdp;

2856
	WARN_ON_ONCE((unsigned long)head & 0x1); /* Misaligned rcu_head! */
2857 2858 2859 2860 2861 2862
	if (debug_rcu_head_queue(head)) {
		/* Probable double call_rcu(), so leak the callback. */
		ACCESS_ONCE(head->func) = rcu_leak_callback;
		WARN_ONCE(1, "__call_rcu(): Leaked duplicate callback\n");
		return;
	}
2863 2864 2865 2866 2867 2868 2869 2870 2871 2872
	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);
2873
	rdp = this_cpu_ptr(rsp->rda);
2874 2875

	/* Add the callback to our list. */
P
Paul E. McKenney 已提交
2876 2877 2878 2879 2880
	if (unlikely(rdp->nxttail[RCU_NEXT_TAIL] == NULL) || cpu != -1) {
		int offline;

		if (cpu != -1)
			rdp = per_cpu_ptr(rsp->rda, cpu);
2881
		offline = !__call_rcu_nocb(rdp, head, lazy, flags);
P
Paul E. McKenney 已提交
2882
		WARN_ON_ONCE(offline);
2883 2884 2885 2886
		/* _call_rcu() is illegal on offline CPU; leak the callback. */
		local_irq_restore(flags);
		return;
	}
2887
	ACCESS_ONCE(rdp->qlen) = rdp->qlen + 1;
2888 2889
	if (lazy)
		rdp->qlen_lazy++;
2890 2891
	else
		rcu_idle_count_callbacks_posted();
2892 2893 2894
	smp_mb();  /* Count before adding callback for rcu_barrier(). */
	*rdp->nxttail[RCU_NEXT_TAIL] = head;
	rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
2895

2896 2897
	if (__is_kfree_rcu_offset((unsigned long)func))
		trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func,
2898
					 rdp->qlen_lazy, rdp->qlen);
2899
	else
2900
		trace_rcu_callback(rsp->name, head, rdp->qlen_lazy, rdp->qlen);
2901

2902 2903
	/* Go handle any RCU core processing required. */
	__call_rcu_core(rsp, rdp, head, flags);
2904 2905 2906 2907
	local_irq_restore(flags);
}

/*
2908
 * Queue an RCU-sched callback for invocation after a grace period.
2909
 */
2910
void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
2911
{
P
Paul E. McKenney 已提交
2912
	__call_rcu(head, func, &rcu_sched_state, -1, 0);
2913
}
2914
EXPORT_SYMBOL_GPL(call_rcu_sched);
2915 2916

/*
2917
 * Queue an RCU callback for invocation after a quicker grace period.
2918 2919 2920
 */
void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
{
P
Paul E. McKenney 已提交
2921
	__call_rcu(head, func, &rcu_bh_state, -1, 0);
2922 2923 2924
}
EXPORT_SYMBOL_GPL(call_rcu_bh);

2925 2926 2927 2928 2929 2930 2931 2932 2933 2934
/*
 * 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))
{
2935
	__call_rcu(head, func, rcu_state_p, -1, 1);
2936 2937 2938
}
EXPORT_SYMBOL_GPL(kfree_call_rcu);

2939 2940 2941 2942 2943 2944 2945 2946 2947 2948 2949
/*
 * 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)
{
2950 2951
	int ret;

2952
	might_sleep();  /* Check for RCU read-side critical section. */
2953 2954 2955 2956
	preempt_disable();
	ret = num_online_cpus() <= 1;
	preempt_enable();
	return ret;
2957 2958
}

2959 2960 2961 2962 2963 2964 2965 2966 2967 2968 2969 2970
/**
 * 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
2971 2972 2973 2974 2975 2976 2977 2978 2979 2980 2981 2982 2983 2984 2985 2986 2987 2988 2989 2990 2991 2992
 * 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).
2993 2994 2995 2996 2997 2998 2999 3000 3001
 *
 * 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)
{
3002 3003 3004 3005
	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");
3006 3007
	if (rcu_blocking_is_gp())
		return;
3008 3009 3010 3011
	if (rcu_expedited)
		synchronize_sched_expedited();
	else
		wait_rcu_gp(call_rcu_sched);
3012 3013 3014 3015 3016 3017 3018 3019 3020 3021 3022
}
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.
3023 3024 3025
 *
 * See the description of synchronize_sched() for more detailed information
 * on memory ordering guarantees.
3026 3027 3028
 */
void synchronize_rcu_bh(void)
{
3029 3030 3031 3032
	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");
3033 3034
	if (rcu_blocking_is_gp())
		return;
3035 3036 3037 3038
	if (rcu_expedited)
		synchronize_rcu_bh_expedited();
	else
		wait_rcu_gp(call_rcu_bh);
3039 3040 3041
}
EXPORT_SYMBOL_GPL(synchronize_rcu_bh);

3042 3043 3044 3045 3046 3047 3048 3049 3050 3051 3052 3053 3054 3055 3056 3057 3058 3059 3060 3061
/**
 * 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().
	 */
3062
	return smp_load_acquire(&rcu_state_p->gpnum);
3063 3064 3065 3066 3067 3068 3069 3070 3071 3072 3073 3074 3075 3076 3077 3078 3079 3080 3081 3082 3083 3084 3085 3086 3087
}
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.
	 */
3088
	newstate = smp_load_acquire(&rcu_state_p->completed);
3089 3090 3091 3092 3093
	if (ULONG_CMP_GE(oldstate, newstate))
		synchronize_rcu();
}
EXPORT_SYMBOL_GPL(cond_synchronize_rcu);

3094 3095 3096 3097 3098 3099 3100 3101 3102 3103 3104 3105 3106 3107 3108 3109 3110
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;
}

3111 3112 3113 3114 3115 3116 3117 3118 3119 3120
/**
 * 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.
3121 3122 3123 3124 3125 3126 3127 3128 3129 3130 3131 3132 3133 3134 3135 3136 3137 3138 3139 3140 3141 3142 3143 3144
 *
 * 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)
{
3145 3146 3147
	cpumask_var_t cm;
	bool cma = false;
	int cpu;
3148 3149
	long firstsnap, s, snap;
	int trycount = 0;
3150
	struct rcu_state *rsp = &rcu_sched_state;
3151

3152 3153 3154 3155 3156 3157 3158 3159
	/*
	 * 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.
	 */
3160 3161
	if (ULONG_CMP_GE((ulong)atomic_long_read(&rsp->expedited_start),
			 (ulong)atomic_long_read(&rsp->expedited_done) +
3162 3163
			 ULONG_MAX / 8)) {
		synchronize_sched();
3164
		atomic_long_inc(&rsp->expedited_wrap);
3165 3166
		return;
	}
3167

3168 3169 3170 3171
	/*
	 * Take a ticket.  Note that atomic_inc_return() implies a
	 * full memory barrier.
	 */
3172
	snap = atomic_long_inc_return(&rsp->expedited_start);
3173
	firstsnap = snap;
3174 3175 3176 3177 3178 3179
	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;
	}
3180
	WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id()));
3181

3182 3183 3184 3185 3186 3187 3188 3189 3190 3191 3192 3193 3194 3195 3196
	/* 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;
	}

3197 3198 3199 3200
	/*
	 * Each pass through the following loop attempts to force a
	 * context switch on each CPU.
	 */
3201
	while (try_stop_cpus(cma ? cm : cpu_online_mask,
3202 3203 3204
			     synchronize_sched_expedited_cpu_stop,
			     NULL) == -EAGAIN) {
		put_online_cpus();
3205
		atomic_long_inc(&rsp->expedited_tryfail);
3206

3207
		/* Check to see if someone else did our work for us. */
3208
		s = atomic_long_read(&rsp->expedited_done);
3209
		if (ULONG_CMP_GE((ulong)s, (ulong)firstsnap)) {
3210
			/* ensure test happens before caller kfree */
3211
			smp_mb__before_atomic(); /* ^^^ */
3212
			atomic_long_inc(&rsp->expedited_workdone1);
3213
			free_cpumask_var(cm);
3214 3215
			return;
		}
3216 3217

		/* No joy, try again later.  Or just synchronize_sched(). */
3218
		if (trycount++ < 10) {
3219
			udelay(trycount * num_online_cpus());
3220
		} else {
3221
			wait_rcu_gp(call_rcu_sched);
3222
			atomic_long_inc(&rsp->expedited_normal);
3223
			free_cpumask_var(cm);
3224 3225 3226
			return;
		}

3227
		/* Recheck to see if someone else did our work for us. */
3228
		s = atomic_long_read(&rsp->expedited_done);
3229
		if (ULONG_CMP_GE((ulong)s, (ulong)firstsnap)) {
3230
			/* ensure test happens before caller kfree */
3231
			smp_mb__before_atomic(); /* ^^^ */
3232
			atomic_long_inc(&rsp->expedited_workdone2);
3233
			free_cpumask_var(cm);
3234 3235 3236 3237 3238
			return;
		}

		/*
		 * Refetching sync_sched_expedited_started allows later
3239 3240 3241 3242
		 * 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.
3243
		 */
3244 3245 3246 3247
		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);
3248
			free_cpumask_var(cm);
3249 3250
			return;
		}
3251
		snap = atomic_long_read(&rsp->expedited_start);
3252 3253
		smp_mb(); /* ensure read is before try_stop_cpus(). */
	}
3254
	atomic_long_inc(&rsp->expedited_stoppedcpus);
3255

3256 3257 3258
all_cpus_idle:
	free_cpumask_var(cm);

3259 3260 3261 3262
	/*
	 * 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
3263
	 * than we did already did their update.
3264 3265
	 */
	do {
3266
		atomic_long_inc(&rsp->expedited_done_tries);
3267
		s = atomic_long_read(&rsp->expedited_done);
3268
		if (ULONG_CMP_GE((ulong)s, (ulong)snap)) {
3269
			/* ensure test happens before caller kfree */
3270
			smp_mb__before_atomic(); /* ^^^ */
3271
			atomic_long_inc(&rsp->expedited_done_lost);
3272 3273
			break;
		}
3274
	} while (atomic_long_cmpxchg(&rsp->expedited_done, s, snap) != s);
3275
	atomic_long_inc(&rsp->expedited_done_exit);
3276 3277 3278 3279 3280

	put_online_cpus();
}
EXPORT_SYMBOL_GPL(synchronize_sched_expedited);

3281 3282 3283 3284 3285 3286 3287 3288 3289
/*
 * 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)
{
3290 3291
	struct rcu_node *rnp = rdp->mynode;

3292 3293 3294 3295 3296
	rdp->n_rcu_pending++;

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

3297 3298 3299 3300
	/* Is this CPU a NO_HZ_FULL CPU that should ignore RCU? */
	if (rcu_nohz_full_cpu(rsp))
		return 0;

3301
	/* Is the RCU core waiting for a quiescent state from this CPU? */
3302
	if (rcu_scheduler_fully_active &&
3303 3304
	    rdp->qs_pending && !rdp->passed_quiesce &&
	    rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_qs_ctr)) {
3305
		rdp->n_rp_qs_pending++;
3306 3307 3308
	} else if (rdp->qs_pending &&
		   (rdp->passed_quiesce ||
		    rdp->rcu_qs_ctr_snap != __this_cpu_read(rcu_qs_ctr))) {
3309
		rdp->n_rp_report_qs++;
3310
		return 1;
3311
	}
3312 3313

	/* Does this CPU have callbacks ready to invoke? */
3314 3315
	if (cpu_has_callbacks_ready_to_invoke(rdp)) {
		rdp->n_rp_cb_ready++;
3316
		return 1;
3317
	}
3318 3319

	/* Has RCU gone idle with this CPU needing another grace period? */
3320 3321
	if (cpu_needs_another_gp(rsp, rdp)) {
		rdp->n_rp_cpu_needs_gp++;
3322
		return 1;
3323
	}
3324 3325

	/* Has another RCU grace period completed?  */
3326
	if (ACCESS_ONCE(rnp->completed) != rdp->completed) { /* outside lock */
3327
		rdp->n_rp_gp_completed++;
3328
		return 1;
3329
	}
3330 3331

	/* Has a new RCU grace period started? */
3332 3333
	if (ACCESS_ONCE(rnp->gpnum) != rdp->gpnum ||
	    unlikely(ACCESS_ONCE(rdp->gpwrap))) { /* outside lock */
3334
		rdp->n_rp_gp_started++;
3335
		return 1;
3336
	}
3337

3338 3339 3340 3341 3342 3343
	/* Does this CPU need a deferred NOCB wakeup? */
	if (rcu_nocb_need_deferred_wakeup(rdp)) {
		rdp->n_rp_nocb_defer_wakeup++;
		return 1;
	}

3344
	/* nothing to do */
3345
	rdp->n_rp_need_nothing++;
3346 3347 3348 3349 3350 3351 3352 3353
	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.
 */
3354
static int rcu_pending(void)
3355
{
3356 3357 3358
	struct rcu_state *rsp;

	for_each_rcu_flavor(rsp)
3359
		if (__rcu_pending(rsp, this_cpu_ptr(rsp->rda)))
3360 3361
			return 1;
	return 0;
3362 3363 3364
}

/*
3365 3366 3367
 * 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.)
3368
 */
3369
static int __maybe_unused rcu_cpu_has_callbacks(bool *all_lazy)
3370
{
3371 3372 3373
	bool al = true;
	bool hc = false;
	struct rcu_data *rdp;
3374 3375
	struct rcu_state *rsp;

3376
	for_each_rcu_flavor(rsp) {
3377
		rdp = this_cpu_ptr(rsp->rda);
3378 3379 3380 3381
		if (!rdp->nxtlist)
			continue;
		hc = true;
		if (rdp->qlen != rdp->qlen_lazy || !all_lazy) {
3382
			al = false;
3383 3384
			break;
		}
3385 3386 3387 3388
	}
	if (all_lazy)
		*all_lazy = al;
	return hc;
3389 3390
}

3391 3392 3393 3394
/*
 * Helper function for _rcu_barrier() tracing.  If tracing is disabled,
 * the compiler is expected to optimize this away.
 */
3395
static void _rcu_barrier_trace(struct rcu_state *rsp, const char *s,
3396 3397 3398 3399 3400 3401
			       int cpu, unsigned long done)
{
	trace_rcu_barrier(rsp->name, s, cpu,
			  atomic_read(&rsp->barrier_cpu_count), done);
}

3402 3403 3404 3405
/*
 * RCU callback function for _rcu_barrier().  If we are last, wake
 * up the task executing _rcu_barrier().
 */
3406
static void rcu_barrier_callback(struct rcu_head *rhp)
3407
{
3408 3409 3410
	struct rcu_data *rdp = container_of(rhp, struct rcu_data, barrier_head);
	struct rcu_state *rsp = rdp->rsp;

3411 3412
	if (atomic_dec_and_test(&rsp->barrier_cpu_count)) {
		_rcu_barrier_trace(rsp, "LastCB", -1, rsp->n_barrier_done);
3413
		complete(&rsp->barrier_completion);
3414 3415 3416
	} else {
		_rcu_barrier_trace(rsp, "CB", -1, rsp->n_barrier_done);
	}
3417 3418 3419 3420 3421 3422 3423
}

/*
 * Called with preemption disabled, and from cross-cpu IRQ context.
 */
static void rcu_barrier_func(void *type)
{
3424
	struct rcu_state *rsp = type;
3425
	struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
3426

3427
	_rcu_barrier_trace(rsp, "IRQ", -1, rsp->n_barrier_done);
3428
	atomic_inc(&rsp->barrier_cpu_count);
3429
	rsp->call(&rdp->barrier_head, rcu_barrier_callback);
3430 3431 3432 3433 3434 3435
}

/*
 * Orchestrate the specified type of RCU barrier, waiting for all
 * RCU callbacks of the specified type to complete.
 */
3436
static void _rcu_barrier(struct rcu_state *rsp)
3437
{
3438 3439
	int cpu;
	struct rcu_data *rdp;
3440 3441
	unsigned long snap = ACCESS_ONCE(rsp->n_barrier_done);
	unsigned long snap_done;
3442

3443
	_rcu_barrier_trace(rsp, "Begin", -1, snap);
3444

3445
	/* Take mutex to serialize concurrent rcu_barrier() requests. */
3446
	mutex_lock(&rsp->barrier_mutex);
3447

3448 3449 3450 3451 3452 3453 3454 3455 3456 3457 3458 3459
	/*
	 * 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.
	 */
3460
	snap_done = rsp->n_barrier_done;
3461
	_rcu_barrier_trace(rsp, "Check", -1, snap_done);
3462 3463 3464 3465 3466 3467 3468 3469 3470 3471 3472 3473

	/*
	 * 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)) {
3474
		_rcu_barrier_trace(rsp, "EarlyExit", -1, snap_done);
3475 3476 3477 3478 3479 3480 3481 3482 3483 3484
		smp_mb(); /* caller's subsequent code after above check. */
		mutex_unlock(&rsp->barrier_mutex);
		return;
	}

	/*
	 * Increment ->n_barrier_done to avoid duplicate work.  Use
	 * ACCESS_ONCE() to prevent the compiler from speculating
	 * the increment to precede the early-exit check.
	 */
3485
	ACCESS_ONCE(rsp->n_barrier_done) = rsp->n_barrier_done + 1;
3486
	WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 1);
3487
	_rcu_barrier_trace(rsp, "Inc1", -1, rsp->n_barrier_done);
3488
	smp_mb(); /* Order ->n_barrier_done increment with below mechanism. */
3489

3490
	/*
3491 3492
	 * 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
3493 3494
	 * (or preemption of this task).  Exclude CPU-hotplug operations
	 * to ensure that no offline CPU has callbacks queued.
3495
	 */
3496
	init_completion(&rsp->barrier_completion);
3497
	atomic_set(&rsp->barrier_cpu_count, 1);
3498
	get_online_cpus();
3499 3500

	/*
3501 3502 3503
	 * 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.
3504
	 */
P
Paul E. McKenney 已提交
3505
	for_each_possible_cpu(cpu) {
3506
		if (!cpu_online(cpu) && !rcu_is_nocb_cpu(cpu))
P
Paul E. McKenney 已提交
3507
			continue;
3508
		rdp = per_cpu_ptr(rsp->rda, cpu);
3509
		if (rcu_is_nocb_cpu(cpu)) {
3510 3511 3512 3513 3514 3515
			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);
3516
				smp_mb__before_atomic();
3517 3518 3519 3520
				atomic_inc(&rsp->barrier_cpu_count);
				__call_rcu(&rdp->barrier_head,
					   rcu_barrier_callback, rsp, cpu, 0);
			}
P
Paul E. McKenney 已提交
3521
		} else if (ACCESS_ONCE(rdp->qlen)) {
3522 3523
			_rcu_barrier_trace(rsp, "OnlineQ", cpu,
					   rsp->n_barrier_done);
3524
			smp_call_function_single(cpu, rcu_barrier_func, rsp, 1);
3525
		} else {
3526 3527
			_rcu_barrier_trace(rsp, "OnlineNQ", cpu,
					   rsp->n_barrier_done);
3528 3529
		}
	}
3530
	put_online_cpus();
3531 3532 3533 3534 3535

	/*
	 * Now that we have an rcu_barrier_callback() callback on each
	 * CPU, and thus each counted, remove the initial count.
	 */
3536
	if (atomic_dec_and_test(&rsp->barrier_cpu_count))
3537
		complete(&rsp->barrier_completion);
3538

3539 3540
	/* Increment ->n_barrier_done to prevent duplicate work. */
	smp_mb(); /* Keep increment after above mechanism. */
3541
	ACCESS_ONCE(rsp->n_barrier_done) = rsp->n_barrier_done + 1;
3542
	WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 0);
3543
	_rcu_barrier_trace(rsp, "Inc2", -1, rsp->n_barrier_done);
3544 3545
	smp_mb(); /* Keep increment before caller's subsequent code. */

3546
	/* Wait for all rcu_barrier_callback() callbacks to be invoked. */
3547
	wait_for_completion(&rsp->barrier_completion);
3548 3549

	/* Other rcu_barrier() invocations can now safely proceed. */
3550
	mutex_unlock(&rsp->barrier_mutex);
3551 3552 3553 3554 3555 3556 3557
}

/**
 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
 */
void rcu_barrier_bh(void)
{
3558
	_rcu_barrier(&rcu_bh_state);
3559 3560 3561 3562 3563 3564 3565 3566
}
EXPORT_SYMBOL_GPL(rcu_barrier_bh);

/**
 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
 */
void rcu_barrier_sched(void)
{
3567
	_rcu_barrier(&rcu_sched_state);
3568 3569 3570
}
EXPORT_SYMBOL_GPL(rcu_barrier_sched);

3571
/*
3572
 * Do boot-time initialization of a CPU's per-CPU RCU data.
3573
 */
3574 3575
static void __init
rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
3576 3577
{
	unsigned long flags;
3578
	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
3579 3580 3581
	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
3582
	raw_spin_lock_irqsave(&rnp->lock, flags);
3583 3584
	rdp->grpmask = 1UL << (cpu - rdp->mynode->grplo);
	rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
3585
	WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE);
3586
	WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1);
3587
	rdp->cpu = cpu;
3588
	rdp->rsp = rsp;
P
Paul E. McKenney 已提交
3589
	rcu_boot_init_nocb_percpu_data(rdp);
P
Paul E. McKenney 已提交
3590
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
3591 3592 3593 3594 3595 3596 3597
}

/*
 * 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.
3598
 */
3599
static void
3600
rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
3601 3602 3603
{
	unsigned long flags;
	unsigned long mask;
3604
	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
3605 3606
	struct rcu_node *rnp = rcu_get_root(rsp);

3607 3608 3609
	/* Exclude new grace periods. */
	mutex_lock(&rsp->onoff_mutex);

3610
	/* Set up local state, ensuring consistent view of global state. */
P
Paul E. McKenney 已提交
3611
	raw_spin_lock_irqsave(&rnp->lock, flags);
3612
	rdp->beenonline = 1;	 /* We have now been online. */
3613 3614
	rdp->qlen_last_fqs_check = 0;
	rdp->n_force_qs_snap = rsp->n_force_qs;
3615
	rdp->blimit = blimit;
3616
	init_callback_list(rdp);  /* Re-enable callbacks on this CPU. */
3617
	rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
3618
	rcu_sysidle_init_percpu_data(rdp->dynticks);
3619 3620
	atomic_set(&rdp->dynticks->dynticks,
		   (atomic_read(&rdp->dynticks->dynticks) & ~0x1) + 1);
P
Paul E. McKenney 已提交
3621
	raw_spin_unlock(&rnp->lock);		/* irqs remain disabled. */
3622 3623 3624 3625 3626 3627

	/* Add CPU to rcu_node bitmasks. */
	rnp = rdp->mynode;
	mask = rdp->grpmask;
	do {
		/* Exclude any attempts to start a new GP on small systems. */
P
Paul E. McKenney 已提交
3628
		raw_spin_lock(&rnp->lock);	/* irqs already disabled. */
3629 3630
		rnp->qsmaskinit |= mask;
		mask = rnp->grpmask;
3631
		if (rnp == rdp->mynode) {
3632 3633 3634 3635 3636 3637
			/*
			 * If there is a grace period in progress, we will
			 * set up to wait for it next time we run the
			 * RCU core code.
			 */
			rdp->gpnum = rnp->completed;
3638
			rdp->completed = rnp->completed;
3639
			rdp->passed_quiesce = 0;
3640
			rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_qs_ctr);
3641
			rdp->qs_pending = 0;
3642
			trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuonl"));
3643
		}
P
Paul E. McKenney 已提交
3644
		raw_spin_unlock(&rnp->lock); /* irqs already disabled. */
3645 3646
		rnp = rnp->parent;
	} while (rnp != NULL && !(rnp->qsmaskinit & mask));
3647
	local_irq_restore(flags);
3648

3649
	mutex_unlock(&rsp->onoff_mutex);
3650 3651
}

3652
static void rcu_prepare_cpu(int cpu)
3653
{
3654 3655 3656
	struct rcu_state *rsp;

	for_each_rcu_flavor(rsp)
3657
		rcu_init_percpu_data(cpu, rsp);
3658 3659 3660
}

/*
3661
 * Handle CPU online/offline notification events.
3662
 */
3663
static int rcu_cpu_notify(struct notifier_block *self,
3664
				    unsigned long action, void *hcpu)
3665 3666
{
	long cpu = (long)hcpu;
3667
	struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
3668
	struct rcu_node *rnp = rdp->mynode;
3669
	struct rcu_state *rsp;
3670 3671 3672 3673

	switch (action) {
	case CPU_UP_PREPARE:
	case CPU_UP_PREPARE_FROZEN:
P
Peter Zijlstra 已提交
3674 3675
		rcu_prepare_cpu(cpu);
		rcu_prepare_kthreads(cpu);
3676
		rcu_spawn_all_nocb_kthreads(cpu);
3677 3678
		break;
	case CPU_ONLINE:
3679
	case CPU_DOWN_FAILED:
T
Thomas Gleixner 已提交
3680
		rcu_boost_kthread_setaffinity(rnp, -1);
3681 3682
		break;
	case CPU_DOWN_PREPARE:
3683
		rcu_boost_kthread_setaffinity(rnp, cpu);
3684
		break;
3685 3686
	case CPU_DYING:
	case CPU_DYING_FROZEN:
3687 3688
		for_each_rcu_flavor(rsp)
			rcu_cleanup_dying_cpu(rsp);
3689
		break;
3690 3691 3692 3693
	case CPU_DEAD:
	case CPU_DEAD_FROZEN:
	case CPU_UP_CANCELED:
	case CPU_UP_CANCELED_FROZEN:
3694
		for_each_rcu_flavor(rsp) {
3695
			rcu_cleanup_dead_cpu(cpu, rsp);
3696 3697
			do_nocb_deferred_wakeup(per_cpu_ptr(rsp->rda, cpu));
		}
3698 3699 3700 3701
		break;
	default:
		break;
	}
3702
	return NOTIFY_OK;
3703 3704
}

3705 3706 3707 3708 3709 3710 3711 3712 3713 3714 3715 3716 3717 3718 3719 3720 3721 3722 3723
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. */
			rcu_expedited = 1;
		break;
	case PM_POST_HIBERNATION:
	case PM_POST_SUSPEND:
		rcu_expedited = 0;
		break;
	default:
		break;
	}
	return NOTIFY_OK;
}

3724
/*
3725
 * Spawn the kthreads that handle each RCU flavor's grace periods.
3726 3727 3728 3729
 */
static int __init rcu_spawn_gp_kthread(void)
{
	unsigned long flags;
3730
	int kthread_prio_in = kthread_prio;
3731 3732
	struct rcu_node *rnp;
	struct rcu_state *rsp;
3733
	struct sched_param sp;
3734 3735
	struct task_struct *t;

3736 3737 3738 3739 3740 3741 3742 3743 3744 3745 3746
	/* 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);

3747
	rcu_scheduler_fully_active = 1;
3748
	for_each_rcu_flavor(rsp) {
3749
		t = kthread_create(rcu_gp_kthread, rsp, "%s", rsp->name);
3750 3751 3752 3753
		BUG_ON(IS_ERR(t));
		rnp = rcu_get_root(rsp);
		raw_spin_lock_irqsave(&rnp->lock, flags);
		rsp->gp_kthread = t;
3754 3755 3756 3757 3758
		if (kthread_prio) {
			sp.sched_priority = kthread_prio;
			sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
		}
		wake_up_process(t);
3759 3760
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
	}
3761
	rcu_spawn_nocb_kthreads();
3762
	rcu_spawn_boost_kthreads();
3763 3764 3765 3766
	return 0;
}
early_initcall(rcu_spawn_gp_kthread);

3767 3768 3769 3770 3771 3772 3773 3774 3775 3776 3777 3778 3779 3780 3781
/*
 * 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;
}

3782 3783 3784 3785 3786 3787 3788 3789 3790
/*
 * Compute the per-level fanout, either using the exact fanout specified
 * or balancing the tree, depending on CONFIG_RCU_FANOUT_EXACT.
 */
#ifdef CONFIG_RCU_FANOUT_EXACT
static void __init rcu_init_levelspread(struct rcu_state *rsp)
{
	int i;

3791 3792
	rsp->levelspread[rcu_num_lvls - 1] = rcu_fanout_leaf;
	for (i = rcu_num_lvls - 2; i >= 0; i--)
3793 3794 3795 3796 3797 3798 3799 3800 3801
		rsp->levelspread[i] = CONFIG_RCU_FANOUT;
}
#else /* #ifdef CONFIG_RCU_FANOUT_EXACT */
static void __init rcu_init_levelspread(struct rcu_state *rsp)
{
	int ccur;
	int cprv;
	int i;

3802
	cprv = nr_cpu_ids;
3803
	for (i = rcu_num_lvls - 1; i >= 0; i--) {
3804 3805 3806 3807 3808 3809 3810 3811 3812 3813
		ccur = rsp->levelcnt[i];
		rsp->levelspread[i] = (cprv + ccur - 1) / ccur;
		cprv = ccur;
	}
}
#endif /* #else #ifdef CONFIG_RCU_FANOUT_EXACT */

/*
 * Helper function for rcu_init() that initializes one rcu_state structure.
 */
3814 3815
static void __init rcu_init_one(struct rcu_state *rsp,
		struct rcu_data __percpu *rda)
3816
{
3817 3818 3819 3820 3821 3822 3823 3824 3825 3826
	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 */
3827
	static u8 fl_mask = 0x1;
3828 3829 3830 3831 3832
	int cpustride = 1;
	int i;
	int j;
	struct rcu_node *rnp;

3833 3834
	BUILD_BUG_ON(MAX_RCU_LVLS > ARRAY_SIZE(buf));  /* Fix buf[] init! */

3835 3836 3837 3838
	/* 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");

3839 3840
	/* Initialize the level-tracking arrays. */

3841 3842 3843
	for (i = 0; i < rcu_num_lvls; i++)
		rsp->levelcnt[i] = num_rcu_lvl[i];
	for (i = 1; i < rcu_num_lvls; i++)
3844 3845
		rsp->level[i] = rsp->level[i - 1] + rsp->levelcnt[i - 1];
	rcu_init_levelspread(rsp);
3846 3847
	rsp->flavor_mask = fl_mask;
	fl_mask <<= 1;
3848 3849 3850

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

3851
	for (i = rcu_num_lvls - 1; i >= 0; i--) {
3852 3853 3854
		cpustride *= rsp->levelspread[i];
		rnp = rsp->level[i];
		for (j = 0; j < rsp->levelcnt[i]; j++, rnp++) {
P
Paul E. McKenney 已提交
3855
			raw_spin_lock_init(&rnp->lock);
3856 3857
			lockdep_set_class_and_name(&rnp->lock,
						   &rcu_node_class[i], buf[i]);
3858 3859 3860
			raw_spin_lock_init(&rnp->fqslock);
			lockdep_set_class_and_name(&rnp->fqslock,
						   &rcu_fqs_class[i], fqs[i]);
3861 3862
			rnp->gpnum = rsp->gpnum;
			rnp->completed = rsp->completed;
3863 3864 3865 3866
			rnp->qsmask = 0;
			rnp->qsmaskinit = 0;
			rnp->grplo = j * cpustride;
			rnp->grphi = (j + 1) * cpustride - 1;
3867 3868
			if (rnp->grphi >= nr_cpu_ids)
				rnp->grphi = nr_cpu_ids - 1;
3869 3870 3871 3872 3873 3874 3875 3876 3877 3878 3879
			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;
3880
			INIT_LIST_HEAD(&rnp->blkd_tasks);
3881
			rcu_init_one_nocb(rnp);
3882 3883
		}
	}
3884

3885
	rsp->rda = rda;
3886
	init_waitqueue_head(&rsp->gp_wq);
3887
	rnp = rsp->level[rcu_num_lvls - 1];
3888
	for_each_possible_cpu(i) {
3889
		while (i > rnp->grphi)
3890
			rnp++;
3891
		per_cpu_ptr(rsp->rda, i)->mynode = rnp;
3892 3893
		rcu_boot_init_percpu_data(i, rsp);
	}
3894
	list_add(&rsp->flavors, &rcu_struct_flavors);
3895 3896
}

3897 3898
/*
 * Compute the rcu_node tree geometry from kernel parameters.  This cannot
3899
 * replace the definitions in tree.h because those are needed to size
3900 3901 3902 3903
 * the ->node array in the rcu_state structure.
 */
static void __init rcu_init_geometry(void)
{
3904
	ulong d;
3905 3906
	int i;
	int j;
3907
	int n = nr_cpu_ids;
3908 3909
	int rcu_capacity[MAX_RCU_LVLS + 1];

3910 3911 3912 3913 3914 3915 3916 3917 3918 3919 3920 3921 3922
	/*
	 * 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;

3923
	/* If the compile-time values are accurate, just leave. */
3924 3925
	if (rcu_fanout_leaf == CONFIG_RCU_FANOUT_LEAF &&
	    nr_cpu_ids == NR_CPUS)
3926
		return;
3927 3928
	pr_info("RCU: Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%d\n",
		rcu_fanout_leaf, nr_cpu_ids);
3929 3930 3931 3932 3933 3934 3935 3936 3937 3938 3939 3940 3941 3942 3943 3944 3945 3946 3947 3948 3949 3950 3951 3952 3953 3954 3955 3956 3957 3958 3959 3960 3961 3962 3963 3964 3965 3966 3967 3968 3969 3970 3971 3972 3973

	/*
	 * 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;
}

3974
void __init rcu_init(void)
3975
{
P
Paul E. McKenney 已提交
3976
	int cpu;
3977

3978
	rcu_bootup_announce();
3979
	rcu_init_geometry();
3980
	rcu_init_one(&rcu_bh_state, &rcu_bh_data);
3981
	rcu_init_one(&rcu_sched_state, &rcu_sched_data);
3982
	__rcu_init_preempt();
J
Jiang Fang 已提交
3983
	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
3984 3985 3986 3987 3988 3989 3990

	/*
	 * 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);
3991
	pm_notifier(rcu_pm_notify, 0);
P
Paul E. McKenney 已提交
3992 3993
	for_each_online_cpu(cpu)
		rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
3994 3995

	rcu_early_boot_tests();
3996 3997
}

3998
#include "tree_plugin.h"