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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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/*
 * 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 */
};

/*
 * 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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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-sched batches processed thus far for debug & stats.
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 */
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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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/*
 * Return the number of RCU BH batches processed thus far for debug & stats.
 */
long rcu_batches_completed_bh(void)
{
	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 */
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	smp_mb__before_atomic();  /* See above. */
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	atomic_inc(&rdtp->dynticks);
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	smp_mb__after_atomic();  /* Force ordering with next sojourn. */
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	WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
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	rcu_dynticks_task_enter();
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	/*
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	 * It is illegal to enter an extended quiescent state while
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	 * 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.");
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}
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/*
 * Enter an RCU extended quiescent state, which can be either the
 * idle loop or adaptive-tickless usermode execution.
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 */
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static void rcu_eqs_enter(bool user)
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{
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	long long oldval;
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	struct rcu_dynticks *rdtp;

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	rdtp = this_cpu_ptr(&rcu_dynticks);
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	oldval = rdtp->dynticks_nesting;
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	WARN_ON_ONCE((oldval & DYNTICK_TASK_NEST_MASK) == 0);
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	if ((oldval & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE) {
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		rdtp->dynticks_nesting = 0;
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		rcu_eqs_enter_common(oldval, user);
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	} else {
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		rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE;
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	}
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}
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/**
 * 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)
{
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	unsigned long flags;

	local_irq_save(flags);
578
	rcu_eqs_enter(false);
579
	rcu_sysidle_enter(0);
580
	local_irq_restore(flags);
581
}
582
EXPORT_SYMBOL_GPL(rcu_idle_enter);
583

584
#ifdef CONFIG_RCU_USER_QS
585 586 587 588 589 590 591 592 593 594
/**
 * 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)
{
595
	rcu_eqs_enter(1);
596
}
597
#endif /* CONFIG_RCU_USER_QS */
598

599 600 601 602 603 604
/**
 * 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.
605
 *
606 607 608 609 610 611 612 613
 * 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.
614
 */
615
void rcu_irq_exit(void)
616 617
{
	unsigned long flags;
618
	long long oldval;
619 620 621
	struct rcu_dynticks *rdtp;

	local_irq_save(flags);
622
	rdtp = this_cpu_ptr(&rcu_dynticks);
623
	oldval = rdtp->dynticks_nesting;
624 625
	rdtp->dynticks_nesting--;
	WARN_ON_ONCE(rdtp->dynticks_nesting < 0);
626
	if (rdtp->dynticks_nesting)
627
		trace_rcu_dyntick(TPS("--="), oldval, rdtp->dynticks_nesting);
628
	else
629 630
		rcu_eqs_enter_common(oldval, true);
	rcu_sysidle_enter(1);
631 632 633 634
	local_irq_restore(flags);
}

/*
635
 * rcu_eqs_exit_common - current CPU moving away from extended quiescent state
636 637 638 639 640
 *
 * 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.
 */
641
static void rcu_eqs_exit_common(long long oldval, int user)
642
{
643 644
	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);

645
	rcu_dynticks_task_exit();
646
	smp_mb__before_atomic();  /* Force ordering w/previous sojourn. */
647 648
	atomic_inc(&rdtp->dynticks);
	/* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
649
	smp_mb__after_atomic();  /* See above. */
650
	WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
651
	rcu_cleanup_after_idle();
652
	trace_rcu_dyntick(TPS("End"), oldval, rdtp->dynticks_nesting);
653
	if (!user && !is_idle_task(current)) {
654 655
		struct task_struct *idle __maybe_unused =
			idle_task(smp_processor_id());
656

657
		trace_rcu_dyntick(TPS("Error on exit: not idle task"),
658
				  oldval, rdtp->dynticks_nesting);
659
		ftrace_dump(DUMP_ORIG);
660 661 662
		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! */
663 664 665
	}
}

666 667 668
/*
 * Exit an RCU extended quiescent state, which can be either the
 * idle loop or adaptive-tickless usermode execution.
669
 */
670
static void rcu_eqs_exit(bool user)
671 672 673 674
{
	struct rcu_dynticks *rdtp;
	long long oldval;

675
	rdtp = this_cpu_ptr(&rcu_dynticks);
676
	oldval = rdtp->dynticks_nesting;
677
	WARN_ON_ONCE(oldval < 0);
678
	if (oldval & DYNTICK_TASK_NEST_MASK) {
679
		rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
680
	} else {
681
		rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
682
		rcu_eqs_exit_common(oldval, user);
683
	}
684
}
685 686 687 688 689 690 691 692 693 694 695 696 697 698

/**
 * 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)
{
699 700 701
	unsigned long flags;

	local_irq_save(flags);
702
	rcu_eqs_exit(false);
703
	rcu_sysidle_exit(0);
704
	local_irq_restore(flags);
705
}
706
EXPORT_SYMBOL_GPL(rcu_idle_exit);
707

708
#ifdef CONFIG_RCU_USER_QS
709 710 711 712 713 714 715 716
/**
 * 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)
{
717
	rcu_eqs_exit(1);
718
}
719
#endif /* CONFIG_RCU_USER_QS */
720

721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746
/**
 * 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);
747
	rdtp = this_cpu_ptr(&rcu_dynticks);
748 749 750
	oldval = rdtp->dynticks_nesting;
	rdtp->dynticks_nesting++;
	WARN_ON_ONCE(rdtp->dynticks_nesting == 0);
751
	if (oldval)
752
		trace_rcu_dyntick(TPS("++="), oldval, rdtp->dynticks_nesting);
753
	else
754 755
		rcu_eqs_exit_common(oldval, true);
	rcu_sysidle_exit(1);
756 757 758 759 760 761
	local_irq_restore(flags);
}

/**
 * rcu_nmi_enter - inform RCU of entry to NMI context
 *
762 763 764 765 766
 * 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.)
767 768 769
 */
void rcu_nmi_enter(void)
{
770
	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
771
	int incby = 2;
772

773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793
	/* 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();
794 795 796 797 798
}

/**
 * rcu_nmi_exit - inform RCU of exit from NMI context
 *
799 800 801 802
 * 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.
803 804 805
 */
void rcu_nmi_exit(void)
{
806
	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
807

808 809 810 811 812 813 814 815 816 817 818 819 820 821
	/*
	 * 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;
822
		return;
823 824 825 826
	}

	/* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
	rdtp->dynticks_nmi_nesting = 0;
827
	/* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
828
	smp_mb__before_atomic();  /* See above. */
829
	atomic_inc(&rdtp->dynticks);
830
	smp_mb__after_atomic();  /* Force delay to next write. */
831
	WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
832 833 834
}

/**
835 836 837 838 839 840 841
 * __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.
 */
842
bool notrace __rcu_is_watching(void)
843 844 845 846 847 848
{
	return atomic_read(this_cpu_ptr(&rcu_dynticks.dynticks)) & 0x1;
}

/**
 * rcu_is_watching - see if RCU thinks that the current CPU is idle
849
 *
850
 * If the current CPU is in its idle loop and is neither in an interrupt
851
 * or NMI handler, return true.
852
 */
853
bool notrace rcu_is_watching(void)
854
{
855
	bool ret;
856 857

	preempt_disable();
858
	ret = __rcu_is_watching();
859 860
	preempt_enable();
	return ret;
861
}
862
EXPORT_SYMBOL_GPL(rcu_is_watching);
863

864
#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
865 866 867 868 869 870 871

/*
 * 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
872 873 874 875 876 877 878 879 880 881 882
 * 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.
883 884 885 886 887 888
 *
 * Disable checking if in an NMI handler because we cannot safely report
 * errors from NMI handlers anyway.
 */
bool rcu_lockdep_current_cpu_online(void)
{
889 890
	struct rcu_data *rdp;
	struct rcu_node *rnp;
891 892 893
	bool ret;

	if (in_nmi())
F
Fengguang Wu 已提交
894
		return true;
895
	preempt_disable();
896
	rdp = this_cpu_ptr(&rcu_sched_data);
897 898
	rnp = rdp->mynode;
	ret = (rdp->grpmask & rnp->qsmaskinit) ||
899 900 901 902 903 904
	      !rcu_scheduler_fully_active;
	preempt_enable();
	return ret;
}
EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);

905
#endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
906

907
/**
908
 * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle
909
 *
910 911 912
 * 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.
913
 */
914
static int rcu_is_cpu_rrupt_from_idle(void)
915
{
916
	return __this_cpu_read(rcu_dynticks.dynticks_nesting) <= 1;
917 918 919 920 921
}

/*
 * Snapshot the specified CPU's dynticks counter so that we can later
 * credit them with an implicit quiescent state.  Return 1 if this CPU
922
 * is in dynticks idle mode, which is an extended quiescent state.
923
 */
924 925
static int dyntick_save_progress_counter(struct rcu_data *rdp,
					 bool *isidle, unsigned long *maxj)
926
{
927
	rdp->dynticks_snap = atomic_add_return(0, &rdp->dynticks->dynticks);
928
	rcu_sysidle_check_cpu(rdp, isidle, maxj);
929 930 931 932 933 934
	if ((rdp->dynticks_snap & 0x1) == 0) {
		trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
		return 1;
	} else {
		return 0;
	}
935 936
}

937 938 939 940 941 942
/*
 * This function really isn't for public consumption, but RCU is special in
 * that context switches can allow the state machine to make progress.
 */
extern void resched_cpu(int cpu);

943 944 945 946
/*
 * 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()
947
 * for this same CPU, or by virtue of having been offline.
948
 */
949 950
static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
				    bool *isidle, unsigned long *maxj)
951
{
952
	unsigned int curr;
953
	int *rcrmp;
954
	unsigned int snap;
955

956 957
	curr = (unsigned int)atomic_add_return(0, &rdp->dynticks->dynticks);
	snap = (unsigned int)rdp->dynticks_snap;
958 959 960 961 962 963 964 965 966

	/*
	 * 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.
	 */
967
	if ((curr & 0x1) == 0 || UINT_CMP_GE(curr, snap + 2)) {
968
		trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
969 970 971 972
		rdp->dynticks_fqs++;
		return 1;
	}

973 974 975 976 977 978 979 980 981 982 983 984 985 986 987
	/*
	 * 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)) {
988
		trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("ofl"));
989 990 991
		rdp->offline_fqs++;
		return 1;
	}
992 993

	/*
994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012
	 * 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.
1013
	 */
1014 1015 1016
	rcrmp = &per_cpu(rcu_sched_qs_mask, rdp->cpu);
	if (ULONG_CMP_GE(jiffies,
			 rdp->rsp->gp_start + jiffies_till_sched_qs) ||
1017
	    ULONG_CMP_GE(jiffies, rdp->rsp->jiffies_resched)) {
1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030
		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. */
		}
1031 1032
	}

1033
	return 0;
1034 1035 1036 1037
}

static void record_gp_stall_check_time(struct rcu_state *rsp)
{
1038
	unsigned long j = jiffies;
1039
	unsigned long j1;
1040 1041 1042

	rsp->gp_start = j;
	smp_wmb(); /* Record start time before stall time. */
1043
	j1 = rcu_jiffies_till_stall_check();
1044
	ACCESS_ONCE(rsp->jiffies_stall) = j + j1;
1045
	rsp->jiffies_resched = j + j1 / 2;
1046
	rsp->n_force_qs_gpstart = ACCESS_ONCE(rsp->n_force_qs);
1047 1048
}

1049
/*
1050
 * Dump stacks of all tasks running on stalled CPUs.
1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068
 */
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);
	}
}

1069
static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum)
1070 1071 1072 1073
{
	int cpu;
	long delta;
	unsigned long flags;
1074 1075
	unsigned long gpa;
	unsigned long j;
1076
	int ndetected = 0;
1077
	struct rcu_node *rnp = rcu_get_root(rsp);
1078
	long totqlen = 0;
1079 1080 1081

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

P
Paul E. McKenney 已提交
1082
	raw_spin_lock_irqsave(&rnp->lock, flags);
1083
	delta = jiffies - ACCESS_ONCE(rsp->jiffies_stall);
1084
	if (delta < RCU_STALL_RAT_DELAY || !rcu_gp_in_progress(rsp)) {
P
Paul E. McKenney 已提交
1085
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
1086 1087
		return;
	}
1088
	ACCESS_ONCE(rsp->jiffies_stall) = jiffies + 3 * rcu_jiffies_till_stall_check() + 3;
P
Paul E. McKenney 已提交
1089
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
1090

1091 1092 1093 1094 1095
	/*
	 * OK, time to rat on our buddy...
	 * See Documentation/RCU/stallwarn.txt for info on how to debug
	 * RCU CPU stall warnings.
	 */
1096
	pr_err("INFO: %s detected stalls on CPUs/tasks:",
1097
	       rsp->name);
1098
	print_cpu_stall_info_begin();
1099
	rcu_for_each_leaf_node(rsp, rnp) {
1100
		raw_spin_lock_irqsave(&rnp->lock, flags);
1101
		ndetected += rcu_print_task_stall(rnp);
1102 1103 1104 1105 1106 1107 1108 1109
		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++;
				}
		}
1110
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
1111
	}
1112 1113 1114 1115 1116 1117 1118

	/*
	 * Now rat on any tasks that got kicked up to the root rcu_node
	 * due to CPU offlining.
	 */
	rnp = rcu_get_root(rsp);
	raw_spin_lock_irqsave(&rnp->lock, flags);
1119
	ndetected += rcu_print_task_stall(rnp);
1120 1121 1122
	raw_spin_unlock_irqrestore(&rnp->lock, flags);

	print_cpu_stall_info_end();
1123 1124
	for_each_possible_cpu(cpu)
		totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen;
1125
	pr_cont("(detected by %d, t=%ld jiffies, g=%ld, c=%ld, q=%lu)\n",
1126
	       smp_processor_id(), (long)(jiffies - rsp->gp_start),
1127
	       (long)rsp->gpnum, (long)rsp->completed, totqlen);
1128
	if (ndetected) {
1129
		rcu_dump_cpu_stacks(rsp);
1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143
	} 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);
			pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld\n",
			       rsp->name, j - gpa, j, gpa,
			       jiffies_till_next_fqs);
			/* In this case, the current CPU might be at fault. */
			sched_show_task(current);
		}
	}
1144

1145
	/* Complain about tasks blocking the grace period. */
1146 1147 1148

	rcu_print_detail_task_stall(rsp);

1149
	force_quiescent_state(rsp);  /* Kick them all. */
1150 1151 1152 1153
}

static void print_cpu_stall(struct rcu_state *rsp)
{
1154
	int cpu;
1155 1156
	unsigned long flags;
	struct rcu_node *rnp = rcu_get_root(rsp);
1157
	long totqlen = 0;
1158

1159 1160 1161 1162 1163
	/*
	 * OK, time to rat on ourselves...
	 * See Documentation/RCU/stallwarn.txt for info on how to debug
	 * RCU CPU stall warnings.
	 */
1164
	pr_err("INFO: %s self-detected stall on CPU", rsp->name);
1165 1166 1167
	print_cpu_stall_info_begin();
	print_cpu_stall_info(rsp, smp_processor_id());
	print_cpu_stall_info_end();
1168 1169
	for_each_possible_cpu(cpu)
		totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen;
1170 1171 1172
	pr_cont(" (t=%lu jiffies g=%ld c=%ld q=%lu)\n",
		jiffies - rsp->gp_start,
		(long)rsp->gpnum, (long)rsp->completed, totqlen);
1173
	rcu_dump_cpu_stacks(rsp);
1174

P
Paul E. McKenney 已提交
1175
	raw_spin_lock_irqsave(&rnp->lock, flags);
1176 1177
	if (ULONG_CMP_GE(jiffies, ACCESS_ONCE(rsp->jiffies_stall)))
		ACCESS_ONCE(rsp->jiffies_stall) = jiffies +
1178
				     3 * rcu_jiffies_till_stall_check() + 3;
P
Paul E. McKenney 已提交
1179
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
1180

1181 1182 1183 1184 1185 1186 1187 1188
	/*
	 * 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());
1189 1190 1191 1192
}

static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
{
1193 1194 1195
	unsigned long completed;
	unsigned long gpnum;
	unsigned long gps;
1196 1197
	unsigned long j;
	unsigned long js;
1198 1199
	struct rcu_node *rnp;

1200
	if (rcu_cpu_stall_suppress || !rcu_gp_in_progress(rsp))
1201
		return;
1202
	j = jiffies;
1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222

	/*
	 * 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... */
1223
	js = ACCESS_ONCE(rsp->jiffies_stall);
1224 1225 1226 1227 1228 1229 1230 1231
	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. */
1232
	rnp = rdp->mynode;
1233
	if (rcu_gp_in_progress(rsp) &&
1234
	    (ACCESS_ONCE(rnp->qsmask) & rdp->grpmask)) {
1235 1236 1237 1238

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

1239 1240
	} else if (rcu_gp_in_progress(rsp) &&
		   ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY)) {
1241

1242
		/* They had a few time units to dump stack, so complain. */
1243
		print_other_cpu_stall(rsp, gpnum);
1244 1245 1246
	}
}

1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257
/**
 * 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)
{
1258 1259 1260
	struct rcu_state *rsp;

	for_each_rcu_flavor(rsp)
1261
		ACCESS_ONCE(rsp->jiffies_stall) = jiffies + ULONG_MAX / 2;
1262 1263
}

1264 1265 1266 1267 1268 1269 1270
/*
 * Initialize the specified rcu_data structure's callback list to empty.
 */
static void init_callback_list(struct rcu_data *rdp)
{
	int i;

1271 1272
	if (init_nocb_callback_list(rdp))
		return;
1273 1274 1275 1276 1277
	rdp->nxtlist = NULL;
	for (i = 0; i < RCU_NEXT_SIZE; i++)
		rdp->nxttail[i] = &rdp->nxtlist;
}

1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295 1296 1297 1298 1299 1300 1301 1302 1303 1304 1305 1306
/*
 * 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;
}

1307 1308 1309 1310 1311
/*
 * 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,
1312
				unsigned long c, const char *s)
1313 1314 1315 1316 1317 1318 1319 1320 1321
{
	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
1322 1323
 * rcu_node structure's ->need_future_gp field.  Returns true if there
 * is reason to awaken the grace-period kthread.
1324 1325 1326
 *
 * The caller must hold the specified rcu_node structure's ->lock.
 */
1327 1328 1329
static bool __maybe_unused
rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
		    unsigned long *c_out)
1330 1331 1332
{
	unsigned long c;
	int i;
1333
	bool ret = false;
1334 1335 1336 1337 1338 1339 1340
	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);
1341
	trace_rcu_future_gp(rnp, rdp, c, TPS("Startleaf"));
1342
	if (rnp->need_future_gp[c & 0x1]) {
1343
		trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartleaf"));
1344
		goto out;
1345 1346 1347 1348 1349 1350 1351
	}

	/*
	 * 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
1352 1353 1354 1355 1356 1357 1358
	 * 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.
1359 1360
	 */
	if (rnp->gpnum != rnp->completed ||
1361
	    ACCESS_ONCE(rnp_root->gpnum) != ACCESS_ONCE(rnp_root->completed)) {
1362
		rnp->need_future_gp[c & 0x1]++;
1363
		trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleaf"));
1364
		goto out;
1365 1366 1367 1368 1369 1370 1371
	}

	/*
	 * 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).
	 */
1372
	if (rnp != rnp_root) {
1373
		raw_spin_lock(&rnp_root->lock);
1374 1375
		smp_mb__after_unlock_lock();
	}
1376 1377 1378 1379 1380 1381 1382 1383 1384 1385 1386 1387 1388 1389 1390 1391 1392

	/*
	 * 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]) {
1393
		trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartedroot"));
1394 1395 1396 1397 1398 1399 1400 1401
		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) {
1402
		trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleafroot"));
1403
	} else {
1404
		trace_rcu_future_gp(rnp, rdp, c, TPS("Startedroot"));
1405
		ret = rcu_start_gp_advanced(rdp->rsp, rnp_root, rdp);
1406 1407 1408 1409
	}
unlock_out:
	if (rnp != rnp_root)
		raw_spin_unlock(&rnp_root->lock);
1410 1411 1412 1413
out:
	if (c_out != NULL)
		*c_out = c;
	return ret;
1414 1415 1416 1417 1418 1419 1420 1421 1422 1423 1424 1425 1426 1427 1428 1429 1430
}

/*
 * 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];
1431 1432
	trace_rcu_future_gp(rnp, rdp, c,
			    needmore ? TPS("CleanupMore") : TPS("Cleanup"));
1433 1434 1435
	return needmore;
}

1436 1437 1438 1439 1440 1441 1442 1443 1444 1445 1446 1447 1448 1449 1450 1451
/*
 * 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);
}

1452 1453 1454 1455 1456 1457 1458
/*
 * 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
1459 1460
 * not hurt to call it repeatedly.  Returns an flag saying that we should
 * awaken the RCU grace-period kthread.
1461 1462 1463
 *
 * The caller must hold rnp->lock with interrupts disabled.
 */
1464
static bool rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
1465 1466 1467 1468
			       struct rcu_data *rdp)
{
	unsigned long c;
	int i;
1469
	bool ret;
1470 1471 1472

	/* If the CPU has no callbacks, nothing to do. */
	if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL])
1473
		return false;
1474 1475 1476 1477 1478 1479 1480 1481 1482 1483 1484 1485 1486 1487 1488 1489 1490 1491 1492 1493 1494 1495 1496 1497 1498 1499 1500 1501

	/*
	 * 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)
1502
		return false;
1503 1504 1505 1506 1507 1508 1509 1510 1511 1512

	/*
	 * 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;
	}
1513
	/* Record any needed additional grace periods. */
1514
	ret = rcu_start_future_gp(rnp, rdp, NULL);
1515 1516 1517

	/* Trace depending on how much we were able to accelerate. */
	if (!*rdp->nxttail[RCU_WAIT_TAIL])
1518
		trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccWaitCB"));
1519
	else
1520
		trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccReadyCB"));
1521
	return ret;
1522 1523 1524 1525 1526 1527 1528 1529
}

/*
 * 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...
1530
 * Returns true if the RCU grace-period kthread needs to be awakened.
1531 1532 1533
 *
 * The caller must hold rnp->lock with interrupts disabled.
 */
1534
static bool rcu_advance_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
1535 1536 1537 1538 1539 1540
			    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])
1541
		return false;
1542 1543 1544 1545 1546 1547 1548 1549 1550 1551 1552 1553 1554 1555 1556 1557 1558 1559 1560 1561 1562 1563 1564

	/*
	 * 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. */
1565
	return rcu_accelerate_cbs(rsp, rnp, rdp);
1566 1567
}

1568
/*
1569 1570 1571
 * 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.
1572
 * Returns true if the grace-period kthread needs to be awakened.
1573
 */
1574 1575
static bool __note_gp_changes(struct rcu_state *rsp, struct rcu_node *rnp,
			      struct rcu_data *rdp)
1576
{
1577 1578
	bool ret;

1579
	/* Handle the ends of any preceding grace periods first. */
1580
	if (rdp->completed == rnp->completed) {
1581

1582
		/* No grace period end, so just accelerate recent callbacks. */
1583
		ret = rcu_accelerate_cbs(rsp, rnp, rdp);
1584

1585 1586 1587
	} else {

		/* Advance callbacks. */
1588
		ret = rcu_advance_cbs(rsp, rnp, rdp);
1589 1590 1591

		/* Remember that we saw this grace-period completion. */
		rdp->completed = rnp->completed;
1592
		trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuend"));
1593
	}
1594

1595 1596 1597 1598 1599 1600 1601
	if (rdp->gpnum != rnp->gpnum) {
		/*
		 * 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;
1602
		trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpustart"));
1603 1604 1605 1606
		rdp->passed_quiesce = 0;
		rdp->qs_pending = !!(rnp->qsmask & rdp->grpmask);
		zero_cpu_stall_ticks(rdp);
	}
1607
	return ret;
1608 1609
}

1610
static void note_gp_changes(struct rcu_state *rsp, struct rcu_data *rdp)
1611 1612
{
	unsigned long flags;
1613
	bool needwake;
1614 1615 1616 1617
	struct rcu_node *rnp;

	local_irq_save(flags);
	rnp = rdp->mynode;
1618 1619
	if ((rdp->gpnum == ACCESS_ONCE(rnp->gpnum) &&
	     rdp->completed == ACCESS_ONCE(rnp->completed)) || /* w/out lock. */
1620 1621 1622 1623
	    !raw_spin_trylock(&rnp->lock)) { /* irqs already off, so later. */
		local_irq_restore(flags);
		return;
	}
1624
	smp_mb__after_unlock_lock();
1625
	needwake = __note_gp_changes(rsp, rnp, rdp);
1626
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
1627 1628
	if (needwake)
		rcu_gp_kthread_wake(rsp);
1629 1630
}

1631
/*
1632
 * Initialize a new grace period.  Return 0 if no grace period required.
1633
 */
1634
static int rcu_gp_init(struct rcu_state *rsp)
1635 1636
{
	struct rcu_data *rdp;
1637
	struct rcu_node *rnp = rcu_get_root(rsp);
1638

1639
	ACCESS_ONCE(rsp->gp_activity) = jiffies;
1640
	rcu_bind_gp_kthread();
1641
	raw_spin_lock_irq(&rnp->lock);
1642
	smp_mb__after_unlock_lock();
1643
	if (!ACCESS_ONCE(rsp->gp_flags)) {
1644 1645 1646 1647
		/* Spurious wakeup, tell caller to go back to sleep.  */
		raw_spin_unlock_irq(&rnp->lock);
		return 0;
	}
1648
	ACCESS_ONCE(rsp->gp_flags) = 0; /* Clear all flags: New grace period. */
1649

1650 1651 1652 1653 1654
	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.
		 */
1655 1656 1657 1658 1659
		raw_spin_unlock_irq(&rnp->lock);
		return 0;
	}

	/* Advance to a new grace period and initialize state. */
1660
	record_gp_stall_check_time(rsp);
1661 1662
	/* Record GP times before starting GP, hence smp_store_release(). */
	smp_store_release(&rsp->gpnum, rsp->gpnum + 1);
1663
	trace_rcu_grace_period(rsp->name, rsp->gpnum, TPS("start"));
1664 1665 1666
	raw_spin_unlock_irq(&rnp->lock);

	/* Exclude any concurrent CPU-hotplug operations. */
1667
	mutex_lock(&rsp->onoff_mutex);
1668
	smp_mb__after_unlock_lock(); /* ->gpnum increment before GP! */
1669 1670 1671 1672 1673 1674 1675 1676 1677 1678 1679 1680 1681 1682 1683

	/*
	 * 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) {
1684
		raw_spin_lock_irq(&rnp->lock);
1685
		smp_mb__after_unlock_lock();
1686
		rdp = this_cpu_ptr(rsp->rda);
1687 1688
		rcu_preempt_check_blocked_tasks(rnp);
		rnp->qsmask = rnp->qsmaskinit;
1689
		ACCESS_ONCE(rnp->gpnum) = rsp->gpnum;
1690
		WARN_ON_ONCE(rnp->completed != rsp->completed);
1691
		ACCESS_ONCE(rnp->completed) = rsp->completed;
1692
		if (rnp == rdp->mynode)
1693
			(void)__note_gp_changes(rsp, rnp, rdp);
1694 1695 1696 1697 1698
		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);
1699
		cond_resched_rcu_qs();
1700
		ACCESS_ONCE(rsp->gp_activity) = jiffies;
1701
	}
1702

1703
	mutex_unlock(&rsp->onoff_mutex);
1704 1705
	return 1;
}
1706

1707 1708 1709
/*
 * Do one round of quiescent-state forcing.
 */
1710
static int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in)
1711 1712
{
	int fqs_state = fqs_state_in;
1713 1714
	bool isidle = false;
	unsigned long maxj;
1715 1716
	struct rcu_node *rnp = rcu_get_root(rsp);

1717
	ACCESS_ONCE(rsp->gp_activity) = jiffies;
1718 1719 1720
	rsp->n_force_qs++;
	if (fqs_state == RCU_SAVE_DYNTICK) {
		/* Collect dyntick-idle snapshots. */
1721
		if (is_sysidle_rcu_state(rsp)) {
1722
			isidle = true;
1723 1724
			maxj = jiffies - ULONG_MAX / 4;
		}
1725 1726
		force_qs_rnp(rsp, dyntick_save_progress_counter,
			     &isidle, &maxj);
1727
		rcu_sysidle_report_gp(rsp, isidle, maxj);
1728 1729 1730
		fqs_state = RCU_FORCE_QS;
	} else {
		/* Handle dyntick-idle and offline CPUs. */
1731
		isidle = false;
1732
		force_qs_rnp(rsp, rcu_implicit_dynticks_qs, &isidle, &maxj);
1733 1734 1735 1736
	}
	/* Clear flag to prevent immediate re-entry. */
	if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
		raw_spin_lock_irq(&rnp->lock);
1737
		smp_mb__after_unlock_lock();
1738 1739
		ACCESS_ONCE(rsp->gp_flags) =
			ACCESS_ONCE(rsp->gp_flags) & ~RCU_GP_FLAG_FQS;
1740 1741 1742 1743 1744
		raw_spin_unlock_irq(&rnp->lock);
	}
	return fqs_state;
}

1745 1746 1747
/*
 * Clean up after the old grace period.
 */
1748
static void rcu_gp_cleanup(struct rcu_state *rsp)
1749 1750
{
	unsigned long gp_duration;
1751
	bool needgp = false;
1752
	int nocb = 0;
1753 1754
	struct rcu_data *rdp;
	struct rcu_node *rnp = rcu_get_root(rsp);
1755

1756
	ACCESS_ONCE(rsp->gp_activity) = jiffies;
1757
	raw_spin_lock_irq(&rnp->lock);
1758
	smp_mb__after_unlock_lock();
1759 1760 1761
	gp_duration = jiffies - rsp->gp_start;
	if (gp_duration > rsp->gp_max)
		rsp->gp_max = gp_duration;
1762

1763 1764 1765 1766 1767 1768 1769 1770
	/*
	 * 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.
	 */
1771
	raw_spin_unlock_irq(&rnp->lock);
1772

1773 1774 1775 1776 1777 1778 1779 1780 1781 1782
	/*
	 * 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) {
1783
		raw_spin_lock_irq(&rnp->lock);
1784
		smp_mb__after_unlock_lock();
1785
		ACCESS_ONCE(rnp->completed) = rsp->gpnum;
1786 1787
		rdp = this_cpu_ptr(rsp->rda);
		if (rnp == rdp->mynode)
1788
			needgp = __note_gp_changes(rsp, rnp, rdp) || needgp;
1789
		/* smp_mb() provided by prior unlock-lock pair. */
1790
		nocb += rcu_future_gp_cleanup(rsp, rnp);
1791
		raw_spin_unlock_irq(&rnp->lock);
1792
		cond_resched_rcu_qs();
1793
		ACCESS_ONCE(rsp->gp_activity) = jiffies;
1794
	}
1795 1796
	rnp = rcu_get_root(rsp);
	raw_spin_lock_irq(&rnp->lock);
1797
	smp_mb__after_unlock_lock(); /* Order GP before ->completed update. */
1798
	rcu_nocb_gp_set(rnp, nocb);
1799

1800 1801
	/* Declare grace period done. */
	ACCESS_ONCE(rsp->completed) = rsp->gpnum;
1802
	trace_rcu_grace_period(rsp->name, rsp->completed, TPS("end"));
1803
	rsp->fqs_state = RCU_GP_IDLE;
1804
	rdp = this_cpu_ptr(rsp->rda);
1805 1806 1807
	/* Advance CBs to reduce false positives below. */
	needgp = rcu_advance_cbs(rsp, rnp, rdp) || needgp;
	if (needgp || cpu_needs_another_gp(rsp, rdp)) {
1808
		ACCESS_ONCE(rsp->gp_flags) = RCU_GP_FLAG_INIT;
1809 1810 1811 1812
		trace_rcu_grace_period(rsp->name,
				       ACCESS_ONCE(rsp->gpnum),
				       TPS("newreq"));
	}
1813 1814 1815 1816 1817 1818 1819 1820
	raw_spin_unlock_irq(&rnp->lock);
}

/*
 * Body of kthread that handles grace periods.
 */
static int __noreturn rcu_gp_kthread(void *arg)
{
1821
	int fqs_state;
1822
	int gf;
1823
	unsigned long j;
1824
	int ret;
1825 1826 1827 1828 1829 1830 1831
	struct rcu_state *rsp = arg;
	struct rcu_node *rnp = rcu_get_root(rsp);

	for (;;) {

		/* Handle grace-period start. */
		for (;;) {
1832 1833 1834
			trace_rcu_grace_period(rsp->name,
					       ACCESS_ONCE(rsp->gpnum),
					       TPS("reqwait"));
1835
			rsp->gp_state = RCU_GP_WAIT_GPS;
1836
			wait_event_interruptible(rsp->gp_wq,
1837
						 ACCESS_ONCE(rsp->gp_flags) &
1838
						 RCU_GP_FLAG_INIT);
1839
			/* Locking provides needed memory barrier. */
1840
			if (rcu_gp_init(rsp))
1841
				break;
1842
			cond_resched_rcu_qs();
1843
			ACCESS_ONCE(rsp->gp_activity) = jiffies;
1844
			WARN_ON(signal_pending(current));
1845 1846 1847
			trace_rcu_grace_period(rsp->name,
					       ACCESS_ONCE(rsp->gpnum),
					       TPS("reqwaitsig"));
1848
		}
1849

1850 1851
		/* Handle quiescent-state forcing. */
		fqs_state = RCU_SAVE_DYNTICK;
1852 1853 1854 1855 1856
		j = jiffies_till_first_fqs;
		if (j > HZ) {
			j = HZ;
			jiffies_till_first_fqs = HZ;
		}
1857
		ret = 0;
1858
		for (;;) {
1859 1860
			if (!ret)
				rsp->jiffies_force_qs = jiffies + j;
1861 1862 1863
			trace_rcu_grace_period(rsp->name,
					       ACCESS_ONCE(rsp->gpnum),
					       TPS("fqswait"));
1864
			rsp->gp_state = RCU_GP_WAIT_FQS;
1865
			ret = wait_event_interruptible_timeout(rsp->gp_wq,
1866 1867
					((gf = ACCESS_ONCE(rsp->gp_flags)) &
					 RCU_GP_FLAG_FQS) ||
1868 1869
					(!ACCESS_ONCE(rnp->qsmask) &&
					 !rcu_preempt_blocked_readers_cgp(rnp)),
1870
					j);
1871
			/* Locking provides needed memory barriers. */
1872
			/* If grace period done, leave loop. */
1873
			if (!ACCESS_ONCE(rnp->qsmask) &&
1874
			    !rcu_preempt_blocked_readers_cgp(rnp))
1875
				break;
1876
			/* If time for quiescent-state forcing, do it. */
1877 1878
			if (ULONG_CMP_GE(jiffies, rsp->jiffies_force_qs) ||
			    (gf & RCU_GP_FLAG_FQS)) {
1879 1880 1881
				trace_rcu_grace_period(rsp->name,
						       ACCESS_ONCE(rsp->gpnum),
						       TPS("fqsstart"));
1882
				fqs_state = rcu_gp_fqs(rsp, fqs_state);
1883 1884 1885
				trace_rcu_grace_period(rsp->name,
						       ACCESS_ONCE(rsp->gpnum),
						       TPS("fqsend"));
1886
				cond_resched_rcu_qs();
1887
				ACCESS_ONCE(rsp->gp_activity) = jiffies;
1888 1889
			} else {
				/* Deal with stray signal. */
1890
				cond_resched_rcu_qs();
1891
				ACCESS_ONCE(rsp->gp_activity) = jiffies;
1892
				WARN_ON(signal_pending(current));
1893 1894 1895
				trace_rcu_grace_period(rsp->name,
						       ACCESS_ONCE(rsp->gpnum),
						       TPS("fqswaitsig"));
1896
			}
1897 1898 1899 1900 1901 1902 1903 1904
			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;
			}
1905
		}
1906 1907 1908

		/* Handle grace-period end. */
		rcu_gp_cleanup(rsp);
1909 1910 1911
	}
}

1912 1913 1914
/*
 * Start a new RCU grace period if warranted, re-initializing the hierarchy
 * in preparation for detecting the next grace period.  The caller must hold
1915
 * the root node's ->lock and hard irqs must be disabled.
1916 1917 1918 1919
 *
 * 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.
1920 1921
 *
 * Returns true if the grace-period kthread must be awakened.
1922
 */
1923
static bool
1924 1925
rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
		      struct rcu_data *rdp)
1926
{
1927
	if (!rsp->gp_kthread || !cpu_needs_another_gp(rsp, rdp)) {
1928
		/*
1929
		 * Either we have not yet spawned the grace-period
1930 1931
		 * task, this CPU does not need another grace period,
		 * or a grace period is already in progress.
1932
		 * Either way, don't start a new grace period.
1933
		 */
1934
		return false;
1935
	}
1936
	ACCESS_ONCE(rsp->gp_flags) = RCU_GP_FLAG_INIT;
1937 1938
	trace_rcu_grace_period(rsp->name, ACCESS_ONCE(rsp->gpnum),
			       TPS("newreq"));
1939

1940 1941
	/*
	 * We can't do wakeups while holding the rnp->lock, as that
1942
	 * could cause possible deadlocks with the rq->lock. Defer
1943
	 * the wakeup to our caller.
1944
	 */
1945
	return true;
1946 1947
}

1948 1949 1950 1951 1952 1953
/*
 * 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.
1954 1955
 *
 * Returns true if the grace-period kthread needs to be awakened.
1956
 */
1957
static bool rcu_start_gp(struct rcu_state *rsp)
1958 1959 1960
{
	struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
	struct rcu_node *rnp = rcu_get_root(rsp);
1961
	bool ret = false;
1962 1963 1964 1965 1966 1967 1968 1969 1970

	/*
	 * 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!
	 */
1971 1972 1973
	ret = rcu_advance_cbs(rsp, rnp, rdp) || ret;
	ret = rcu_start_gp_advanced(rsp, rnp, rdp) || ret;
	return ret;
1974 1975
}

1976
/*
P
Paul E. McKenney 已提交
1977 1978 1979
 * 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
1980 1981
 * if one is needed.  Note that the caller must hold rnp->lock, which
 * is released before return.
1982
 */
P
Paul E. McKenney 已提交
1983
static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
1984
	__releases(rcu_get_root(rsp)->lock)
1985
{
1986
	WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
1987
	raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags);
1988
	rcu_gp_kthread_wake(rsp);
1989 1990
}

1991
/*
P
Paul E. McKenney 已提交
1992 1993 1994 1995 1996 1997
 * 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.
1998 1999
 */
static void
P
Paul E. McKenney 已提交
2000 2001
rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
		  struct rcu_node *rnp, unsigned long flags)
2002 2003
	__releases(rnp->lock)
{
2004 2005
	struct rcu_node *rnp_c;

2006 2007 2008 2009 2010
	/* 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
2011
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
2012 2013 2014
			return;
		}
		rnp->qsmask &= ~mask;
2015 2016 2017 2018
		trace_rcu_quiescent_state_report(rsp->name, rnp->gpnum,
						 mask, rnp->qsmask, rnp->level,
						 rnp->grplo, rnp->grphi,
						 !!rnp->gp_tasks);
2019
		if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
2020 2021

			/* Other bits still set at this level, so done. */
P
Paul E. McKenney 已提交
2022
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
2023 2024 2025 2026 2027 2028 2029 2030 2031
			return;
		}
		mask = rnp->grpmask;
		if (rnp->parent == NULL) {

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

			break;
		}
P
Paul E. McKenney 已提交
2032
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
2033
		rnp_c = rnp;
2034
		rnp = rnp->parent;
P
Paul E. McKenney 已提交
2035
		raw_spin_lock_irqsave(&rnp->lock, flags);
2036
		smp_mb__after_unlock_lock();
2037
		WARN_ON_ONCE(rnp_c->qsmask);
2038 2039 2040 2041
	}

	/*
	 * Get here if we are the last CPU to pass through a quiescent
P
Paul E. McKenney 已提交
2042
	 * state for this grace period.  Invoke rcu_report_qs_rsp()
2043
	 * to clean up and start the next grace period if one is needed.
2044
	 */
P
Paul E. McKenney 已提交
2045
	rcu_report_qs_rsp(rsp, flags); /* releases rnp->lock. */
2046 2047 2048
}

/*
P
Paul E. McKenney 已提交
2049 2050 2051 2052 2053 2054 2055
 * 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!
2056 2057
 */
static void
2058
rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp)
2059 2060 2061
{
	unsigned long flags;
	unsigned long mask;
2062
	bool needwake;
2063 2064 2065
	struct rcu_node *rnp;

	rnp = rdp->mynode;
P
Paul E. McKenney 已提交
2066
	raw_spin_lock_irqsave(&rnp->lock, flags);
2067
	smp_mb__after_unlock_lock();
2068 2069
	if (rdp->passed_quiesce == 0 || rdp->gpnum != rnp->gpnum ||
	    rnp->completed == rnp->gpnum) {
2070 2071

		/*
2072 2073 2074 2075
		 * 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.
2076
		 */
2077
		rdp->passed_quiesce = 0;	/* need qs for new gp. */
P
Paul E. McKenney 已提交
2078
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
2079 2080 2081 2082
		return;
	}
	mask = rdp->grpmask;
	if ((rnp->qsmask & mask) == 0) {
P
Paul E. McKenney 已提交
2083
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
2084 2085 2086 2087 2088 2089 2090
	} 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.
		 */
2091
		needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
2092

P
Paul E. McKenney 已提交
2093
		rcu_report_qs_rnp(mask, rsp, rnp, flags); /* rlses rnp->lock */
2094 2095
		if (needwake)
			rcu_gp_kthread_wake(rsp);
2096 2097 2098 2099 2100 2101 2102 2103 2104 2105 2106 2107
	}
}

/*
 * 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)
{
2108 2109
	/* Check for grace-period ends and beginnings. */
	note_gp_changes(rsp, rdp);
2110 2111 2112 2113 2114 2115 2116 2117 2118 2119 2120 2121

	/*
	 * 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.
	 */
2122
	if (!rdp->passed_quiesce)
2123 2124
		return;

P
Paul E. McKenney 已提交
2125 2126 2127 2128
	/*
	 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
	 * judge of that).
	 */
2129
	rcu_report_qs_rdp(rdp->cpu, rsp, rdp);
2130 2131 2132 2133
}

#ifdef CONFIG_HOTPLUG_CPU

2134
/*
2135 2136
 * Send the specified CPU's RCU callbacks to the orphanage.  The
 * specified CPU must be offline, and the caller must hold the
2137
 * ->orphan_lock.
2138
 */
2139 2140 2141
static void
rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
			  struct rcu_node *rnp, struct rcu_data *rdp)
2142
{
P
Paul E. McKenney 已提交
2143
	/* No-CBs CPUs do not have orphanable callbacks. */
2144
	if (rcu_is_nocb_cpu(rdp->cpu))
P
Paul E. McKenney 已提交
2145 2146
		return;

2147 2148
	/*
	 * Orphan the callbacks.  First adjust the counts.  This is safe
2149 2150
	 * because _rcu_barrier() excludes CPU-hotplug operations, so it
	 * cannot be running now.  Thus no memory barrier is required.
2151
	 */
2152
	if (rdp->nxtlist != NULL) {
2153 2154 2155
		rsp->qlen_lazy += rdp->qlen_lazy;
		rsp->qlen += rdp->qlen;
		rdp->n_cbs_orphaned += rdp->qlen;
2156
		rdp->qlen_lazy = 0;
2157
		ACCESS_ONCE(rdp->qlen) = 0;
2158 2159 2160
	}

	/*
2161 2162 2163 2164 2165 2166 2167
	 * 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.
2168
	 */
2169 2170 2171 2172
	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;
2173 2174 2175
	}

	/*
2176 2177 2178
	 * 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.
2179
	 */
2180
	if (rdp->nxtlist != NULL) {
2181 2182
		*rsp->orphan_donetail = rdp->nxtlist;
		rsp->orphan_donetail = rdp->nxttail[RCU_DONE_TAIL];
2183
	}
2184

2185
	/* Finally, initialize the rcu_data structure's list to empty.  */
2186
	init_callback_list(rdp);
2187 2188 2189 2190
}

/*
 * Adopt the RCU callbacks from the specified rcu_state structure's
2191
 * orphanage.  The caller must hold the ->orphan_lock.
2192
 */
2193
static void rcu_adopt_orphan_cbs(struct rcu_state *rsp, unsigned long flags)
2194 2195
{
	int i;
2196
	struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
2197

P
Paul E. McKenney 已提交
2198
	/* No-CBs CPUs are handled specially. */
2199
	if (rcu_nocb_adopt_orphan_cbs(rsp, rdp, flags))
P
Paul E. McKenney 已提交
2200 2201
		return;

2202 2203 2204 2205
	/* Do the accounting first. */
	rdp->qlen_lazy += rsp->qlen_lazy;
	rdp->qlen += rsp->qlen;
	rdp->n_cbs_adopted += rsp->qlen;
2206 2207
	if (rsp->qlen_lazy != rsp->qlen)
		rcu_idle_count_callbacks_posted();
2208 2209 2210 2211 2212 2213 2214 2215 2216 2217 2218 2219 2220 2221 2222 2223 2224 2225 2226 2227 2228 2229 2230 2231 2232 2233 2234 2235 2236 2237 2238 2239 2240 2241 2242 2243 2244 2245 2246
	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);
2247 2248
	trace_rcu_grace_period(rsp->name,
			       rnp->gpnum + 1 - !!(rnp->qsmask & mask),
2249
			       TPS("cpuofl"));
2250 2251 2252
}

/*
2253
 * The CPU has been completely removed, and some other CPU is reporting
2254 2255
 * this fact from process context.  Do the remainder of the cleanup,
 * including orphaning the outgoing CPU's RCU callbacks, and also
2256 2257
 * 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.
2258
 */
2259
static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
2260
{
2261 2262 2263
	unsigned long flags;
	unsigned long mask;
	int need_report = 0;
2264
	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
2265
	struct rcu_node *rnp = rdp->mynode;  /* Outgoing CPU's rdp & rnp. */
2266

2267
	/* Adjust any no-longer-needed kthreads. */
T
Thomas Gleixner 已提交
2268
	rcu_boost_kthread_setaffinity(rnp, -1);
2269 2270

	/* Exclude any attempts to start a new grace period. */
2271
	mutex_lock(&rsp->onoff_mutex);
2272
	raw_spin_lock_irqsave(&rsp->orphan_lock, flags);
2273

2274 2275
	/* Orphan the dead CPU's callbacks, and adopt them if appropriate. */
	rcu_send_cbs_to_orphanage(cpu, rsp, rnp, rdp);
2276
	rcu_adopt_orphan_cbs(rsp, flags);
2277

2278 2279 2280 2281
	/* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */
	mask = rdp->grpmask;	/* rnp->grplo is constant. */
	do {
		raw_spin_lock(&rnp->lock);	/* irqs already disabled. */
2282
		smp_mb__after_unlock_lock();
2283 2284 2285 2286 2287 2288 2289 2290 2291 2292 2293 2294 2295 2296 2297 2298 2299
		rnp->qsmaskinit &= ~mask;
		if (rnp->qsmaskinit != 0) {
			if (rnp != rdp->mynode)
				raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
			break;
		}
		if (rnp == rdp->mynode)
			need_report = rcu_preempt_offline_tasks(rsp, rnp, rdp);
		else
			raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
		mask = rnp->grpmask;
		rnp = rnp->parent;
	} while (rnp != NULL);

	/*
	 * We still hold the leaf rcu_node structure lock here, and
	 * irqs are still disabled.  The reason for this subterfuge is
2300
	 * because invoking rcu_report_unblock_qs_rnp() with ->orphan_lock
2301 2302
	 * held leads to deadlock.
	 */
2303
	raw_spin_unlock(&rsp->orphan_lock); /* irqs remain disabled. */
2304 2305 2306 2307 2308 2309 2310
	rnp = rdp->mynode;
	if (need_report & RCU_OFL_TASKS_NORM_GP)
		rcu_report_unblock_qs_rnp(rnp, flags);
	else
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
	if (need_report & RCU_OFL_TASKS_EXP_GP)
		rcu_report_exp_rnp(rsp, rnp, true);
2311 2312 2313
	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);
2314 2315 2316
	init_callback_list(rdp);
	/* Disallow further callbacks on this CPU. */
	rdp->nxttail[RCU_NEXT_TAIL] = NULL;
2317
	mutex_unlock(&rsp->onoff_mutex);
2318 2319 2320 2321
}

#else /* #ifdef CONFIG_HOTPLUG_CPU */

2322
static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
2323 2324 2325
{
}

2326
static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
2327 2328 2329 2330 2331 2332 2333 2334 2335
{
}

#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.
 */
2336
static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
2337 2338 2339
{
	unsigned long flags;
	struct rcu_head *next, *list, **tail;
E
Eric Dumazet 已提交
2340 2341
	long bl, count, count_lazy;
	int i;
2342

2343
	/* If no callbacks are ready, just return. */
2344
	if (!cpu_has_callbacks_ready_to_invoke(rdp)) {
2345
		trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, 0);
2346 2347 2348
		trace_rcu_batch_end(rsp->name, 0, !!ACCESS_ONCE(rdp->nxtlist),
				    need_resched(), is_idle_task(current),
				    rcu_is_callbacks_kthread());
2349
		return;
2350
	}
2351 2352 2353 2354 2355 2356

	/*
	 * Extract the list of ready callbacks, disabling to prevent
	 * races with call_rcu() from interrupt handlers.
	 */
	local_irq_save(flags);
2357
	WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
2358
	bl = rdp->blimit;
2359
	trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, bl);
2360 2361 2362 2363
	list = rdp->nxtlist;
	rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
	*rdp->nxttail[RCU_DONE_TAIL] = NULL;
	tail = rdp->nxttail[RCU_DONE_TAIL];
2364 2365 2366
	for (i = RCU_NEXT_SIZE - 1; i >= 0; i--)
		if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
			rdp->nxttail[i] = &rdp->nxtlist;
2367 2368 2369
	local_irq_restore(flags);

	/* Invoke callbacks. */
2370
	count = count_lazy = 0;
2371 2372 2373
	while (list) {
		next = list->next;
		prefetch(next);
2374
		debug_rcu_head_unqueue(list);
2375 2376
		if (__rcu_reclaim(rsp->name, list))
			count_lazy++;
2377
		list = next;
2378 2379 2380 2381
		/* Stop only if limit reached and CPU has something to do. */
		if (++count >= bl &&
		    (need_resched() ||
		     (!is_idle_task(current) && !rcu_is_callbacks_kthread())))
2382 2383 2384 2385
			break;
	}

	local_irq_save(flags);
2386 2387 2388
	trace_rcu_batch_end(rsp->name, count, !!list, need_resched(),
			    is_idle_task(current),
			    rcu_is_callbacks_kthread());
2389 2390 2391 2392 2393

	/* Update count, and requeue any remaining callbacks. */
	if (list != NULL) {
		*tail = rdp->nxtlist;
		rdp->nxtlist = list;
2394 2395 2396
		for (i = 0; i < RCU_NEXT_SIZE; i++)
			if (&rdp->nxtlist == rdp->nxttail[i])
				rdp->nxttail[i] = tail;
2397 2398 2399
			else
				break;
	}
2400 2401
	smp_mb(); /* List handling before counting for rcu_barrier(). */
	rdp->qlen_lazy -= count_lazy;
2402
	ACCESS_ONCE(rdp->qlen) = rdp->qlen - count;
2403
	rdp->n_cbs_invoked += count;
2404 2405 2406 2407 2408

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

2409 2410 2411 2412 2413 2414
	/* 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;
2415
	WARN_ON_ONCE((rdp->nxtlist == NULL) != (rdp->qlen == 0));
2416

2417 2418
	local_irq_restore(flags);

2419
	/* Re-invoke RCU core processing if there are callbacks remaining. */
2420
	if (cpu_has_callbacks_ready_to_invoke(rdp))
2421
		invoke_rcu_core();
2422 2423 2424 2425 2426
}

/*
 * 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).
2427
 * Also schedule RCU core processing.
2428
 *
2429
 * This function must be called from hardirq context.  It is normally
2430 2431 2432
 * invoked from the scheduling-clock interrupt.  If rcu_pending returns
 * false, there is no point in invoking rcu_check_callbacks().
 */
2433
void rcu_check_callbacks(int user)
2434
{
2435
	trace_rcu_utilization(TPS("Start scheduler-tick"));
2436
	increment_cpu_stall_ticks();
2437
	if (user || rcu_is_cpu_rrupt_from_idle()) {
2438 2439 2440 2441 2442

		/*
		 * 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
2443
		 * a quiescent state, so note it.
2444 2445
		 *
		 * No memory barrier is required here because both
2446 2447 2448
		 * 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.
2449 2450
		 */

2451 2452
		rcu_sched_qs();
		rcu_bh_qs();
2453 2454 2455 2456 2457 2458 2459

	} 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
2460
		 * critical section, so note it.
2461 2462
		 */

2463
		rcu_bh_qs();
2464
	}
2465
	rcu_preempt_check_callbacks();
2466
	if (rcu_pending())
2467
		invoke_rcu_core();
P
Paul E. McKenney 已提交
2468 2469
	if (user)
		rcu_note_voluntary_context_switch(current);
2470
	trace_rcu_utilization(TPS("End scheduler-tick"));
2471 2472 2473 2474 2475
}

/*
 * Scan the leaf rcu_node structures, processing dyntick state for any that
 * have not yet encountered a quiescent state, using the function specified.
2476 2477
 * Also initiate boosting for any threads blocked on the root rcu_node.
 *
2478
 * The caller must have suppressed start of new grace periods.
2479
 */
2480 2481 2482 2483
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)
2484 2485 2486 2487 2488
{
	unsigned long bit;
	int cpu;
	unsigned long flags;
	unsigned long mask;
2489
	struct rcu_node *rnp;
2490

2491
	rcu_for_each_leaf_node(rsp, rnp) {
2492
		cond_resched_rcu_qs();
2493
		mask = 0;
P
Paul E. McKenney 已提交
2494
		raw_spin_lock_irqsave(&rnp->lock, flags);
2495
		smp_mb__after_unlock_lock();
2496
		if (!rcu_gp_in_progress(rsp)) {
P
Paul E. McKenney 已提交
2497
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
2498
			return;
2499
		}
2500
		if (rnp->qsmask == 0) {
2501
			rcu_initiate_boost(rnp, flags); /* releases rnp->lock */
2502 2503
			continue;
		}
2504
		cpu = rnp->grplo;
2505
		bit = 1;
2506
		for (; cpu <= rnp->grphi; cpu++, bit <<= 1) {
2507 2508
			if ((rnp->qsmask & bit) != 0) {
				if ((rnp->qsmaskinit & bit) != 0)
2509
					*isidle = false;
2510 2511 2512
				if (f(per_cpu_ptr(rsp->rda, cpu), isidle, maxj))
					mask |= bit;
			}
2513
		}
2514
		if (mask != 0) {
2515

P
Paul E. McKenney 已提交
2516 2517
			/* rcu_report_qs_rnp() releases rnp->lock. */
			rcu_report_qs_rnp(mask, rsp, rnp, flags);
2518 2519
			continue;
		}
P
Paul E. McKenney 已提交
2520
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
2521
	}
2522
	rnp = rcu_get_root(rsp);
2523 2524
	if (rnp->qsmask == 0) {
		raw_spin_lock_irqsave(&rnp->lock, flags);
2525
		smp_mb__after_unlock_lock();
2526 2527
		rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */
	}
2528 2529 2530 2531 2532 2533
}

/*
 * Force quiescent states on reluctant CPUs, and also detect which
 * CPUs are in dyntick-idle mode.
 */
2534
static void force_quiescent_state(struct rcu_state *rsp)
2535 2536
{
	unsigned long flags;
2537 2538 2539 2540 2541
	bool ret;
	struct rcu_node *rnp;
	struct rcu_node *rnp_old = NULL;

	/* Funnel through hierarchy to reduce memory contention. */
2542
	rnp = __this_cpu_read(rsp->rda->mynode);
2543 2544 2545 2546 2547 2548
	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) {
2549
			rsp->n_force_qs_lh++;
2550 2551 2552 2553 2554
			return;
		}
		rnp_old = rnp;
	}
	/* rnp_old == rcu_get_root(rsp), rnp == NULL. */
2555

2556 2557
	/* Reached the root of the rcu_node tree, acquire lock. */
	raw_spin_lock_irqsave(&rnp_old->lock, flags);
2558
	smp_mb__after_unlock_lock();
2559 2560
	raw_spin_unlock(&rnp_old->fqslock);
	if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
2561
		rsp->n_force_qs_lh++;
2562
		raw_spin_unlock_irqrestore(&rnp_old->lock, flags);
2563
		return;  /* Someone beat us to it. */
2564
	}
2565 2566
	ACCESS_ONCE(rsp->gp_flags) =
		ACCESS_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS;
2567
	raw_spin_unlock_irqrestore(&rnp_old->lock, flags);
2568
	rcu_gp_kthread_wake(rsp);
2569 2570 2571
}

/*
2572 2573 2574
 * 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.
2575 2576
 */
static void
2577
__rcu_process_callbacks(struct rcu_state *rsp)
2578 2579
{
	unsigned long flags;
2580
	bool needwake;
2581
	struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
2582

2583 2584
	WARN_ON_ONCE(rdp->beenonline == 0);

2585 2586 2587 2588
	/* 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? */
2589
	local_irq_save(flags);
2590
	if (cpu_needs_another_gp(rsp, rdp)) {
2591
		raw_spin_lock(&rcu_get_root(rsp)->lock); /* irqs disabled. */
2592
		needwake = rcu_start_gp(rsp);
2593
		raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags);
2594 2595
		if (needwake)
			rcu_gp_kthread_wake(rsp);
2596 2597
	} else {
		local_irq_restore(flags);
2598 2599 2600
	}

	/* If there are callbacks ready, invoke them. */
2601
	if (cpu_has_callbacks_ready_to_invoke(rdp))
2602
		invoke_rcu_callbacks(rsp, rdp);
2603 2604 2605

	/* Do any needed deferred wakeups of rcuo kthreads. */
	do_nocb_deferred_wakeup(rdp);
2606 2607
}

2608
/*
2609
 * Do RCU core processing for the current CPU.
2610
 */
2611
static void rcu_process_callbacks(struct softirq_action *unused)
2612
{
2613 2614
	struct rcu_state *rsp;

2615 2616
	if (cpu_is_offline(smp_processor_id()))
		return;
2617
	trace_rcu_utilization(TPS("Start RCU core"));
2618 2619
	for_each_rcu_flavor(rsp)
		__rcu_process_callbacks(rsp);
2620
	trace_rcu_utilization(TPS("End RCU core"));
2621 2622
}

2623
/*
2624 2625 2626 2627 2628
 * 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
 * are running on the current CPU with interrupts disabled, the
 * rcu_cpu_kthread_task cannot disappear out from under us.
2629
 */
2630
static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
2631
{
2632 2633
	if (unlikely(!ACCESS_ONCE(rcu_scheduler_fully_active)))
		return;
2634 2635
	if (likely(!rsp->boost)) {
		rcu_do_batch(rsp, rdp);
2636 2637
		return;
	}
2638
	invoke_rcu_callbacks_kthread();
2639 2640
}

2641
static void invoke_rcu_core(void)
2642
{
2643 2644
	if (cpu_online(smp_processor_id()))
		raise_softirq(RCU_SOFTIRQ);
2645 2646
}

2647 2648 2649 2650 2651
/*
 * 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)
2652
{
2653 2654
	bool needwake;

2655 2656 2657 2658
	/*
	 * If called from an extended quiescent state, invoke the RCU
	 * core in order to force a re-evaluation of RCU's idleness.
	 */
2659
	if (!rcu_is_watching() && cpu_online(smp_processor_id()))
2660 2661
		invoke_rcu_core();

2662
	/* If interrupts were disabled or CPU offline, don't invoke RCU core. */
2663
	if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
2664
		return;
2665

2666 2667 2668 2669 2670 2671 2672
	/*
	 * 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.
	 */
2673
	if (unlikely(rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) {
2674 2675

		/* Are we ignoring a completed grace period? */
2676
		note_gp_changes(rsp, rdp);
2677 2678 2679 2680 2681

		/* 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);

2682
			raw_spin_lock(&rnp_root->lock);
2683
			smp_mb__after_unlock_lock();
2684
			needwake = rcu_start_gp(rsp);
2685
			raw_spin_unlock(&rnp_root->lock);
2686 2687
			if (needwake)
				rcu_gp_kthread_wake(rsp);
2688 2689 2690 2691 2692
		} 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)
2693
				force_quiescent_state(rsp);
2694 2695 2696
			rdp->n_force_qs_snap = rsp->n_force_qs;
			rdp->qlen_last_fqs_check = rdp->qlen;
		}
2697
	}
2698 2699
}

2700 2701 2702 2703 2704 2705 2706
/*
 * RCU callback function to leak a callback.
 */
static void rcu_leak_callback(struct rcu_head *rhp)
{
}

P
Paul E. McKenney 已提交
2707 2708 2709 2710 2711 2712
/*
 * 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.
 */
2713 2714
static void
__call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
P
Paul E. McKenney 已提交
2715
	   struct rcu_state *rsp, int cpu, bool lazy)
2716 2717 2718 2719
{
	unsigned long flags;
	struct rcu_data *rdp;

2720
	WARN_ON_ONCE((unsigned long)head & 0x1); /* Misaligned rcu_head! */
2721 2722 2723 2724 2725 2726
	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;
	}
2727 2728 2729 2730 2731 2732 2733 2734 2735 2736
	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);
2737
	rdp = this_cpu_ptr(rsp->rda);
2738 2739

	/* Add the callback to our list. */
P
Paul E. McKenney 已提交
2740 2741 2742 2743 2744
	if (unlikely(rdp->nxttail[RCU_NEXT_TAIL] == NULL) || cpu != -1) {
		int offline;

		if (cpu != -1)
			rdp = per_cpu_ptr(rsp->rda, cpu);
2745
		offline = !__call_rcu_nocb(rdp, head, lazy, flags);
P
Paul E. McKenney 已提交
2746
		WARN_ON_ONCE(offline);
2747 2748 2749 2750
		/* _call_rcu() is illegal on offline CPU; leak the callback. */
		local_irq_restore(flags);
		return;
	}
2751
	ACCESS_ONCE(rdp->qlen) = rdp->qlen + 1;
2752 2753
	if (lazy)
		rdp->qlen_lazy++;
2754 2755
	else
		rcu_idle_count_callbacks_posted();
2756 2757 2758
	smp_mb();  /* Count before adding callback for rcu_barrier(). */
	*rdp->nxttail[RCU_NEXT_TAIL] = head;
	rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
2759

2760 2761
	if (__is_kfree_rcu_offset((unsigned long)func))
		trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func,
2762
					 rdp->qlen_lazy, rdp->qlen);
2763
	else
2764
		trace_rcu_callback(rsp->name, head, rdp->qlen_lazy, rdp->qlen);
2765

2766 2767
	/* Go handle any RCU core processing required. */
	__call_rcu_core(rsp, rdp, head, flags);
2768 2769 2770 2771
	local_irq_restore(flags);
}

/*
2772
 * Queue an RCU-sched callback for invocation after a grace period.
2773
 */
2774
void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
2775
{
P
Paul E. McKenney 已提交
2776
	__call_rcu(head, func, &rcu_sched_state, -1, 0);
2777
}
2778
EXPORT_SYMBOL_GPL(call_rcu_sched);
2779 2780

/*
2781
 * Queue an RCU callback for invocation after a quicker grace period.
2782 2783 2784
 */
void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
{
P
Paul E. McKenney 已提交
2785
	__call_rcu(head, func, &rcu_bh_state, -1, 0);
2786 2787 2788
}
EXPORT_SYMBOL_GPL(call_rcu_bh);

2789 2790 2791 2792 2793 2794 2795 2796 2797 2798
/*
 * 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))
{
2799
	__call_rcu(head, func, rcu_state_p, -1, 1);
2800 2801 2802
}
EXPORT_SYMBOL_GPL(kfree_call_rcu);

2803 2804 2805 2806 2807 2808 2809 2810 2811 2812 2813
/*
 * 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)
{
2814 2815
	int ret;

2816
	might_sleep();  /* Check for RCU read-side critical section. */
2817 2818 2819 2820
	preempt_disable();
	ret = num_online_cpus() <= 1;
	preempt_enable();
	return ret;
2821 2822
}

2823 2824 2825 2826 2827 2828 2829 2830 2831 2832 2833 2834
/**
 * 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
2835 2836 2837 2838 2839 2840 2841 2842 2843 2844 2845 2846 2847 2848 2849 2850 2851 2852 2853 2854 2855 2856
 * 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).
2857 2858 2859 2860 2861 2862 2863 2864 2865
 *
 * 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)
{
2866 2867 2868 2869
	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");
2870 2871
	if (rcu_blocking_is_gp())
		return;
2872 2873 2874 2875
	if (rcu_expedited)
		synchronize_sched_expedited();
	else
		wait_rcu_gp(call_rcu_sched);
2876 2877 2878 2879 2880 2881 2882 2883 2884 2885 2886
}
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.
2887 2888 2889
 *
 * See the description of synchronize_sched() for more detailed information
 * on memory ordering guarantees.
2890 2891 2892
 */
void synchronize_rcu_bh(void)
{
2893 2894 2895 2896
	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");
2897 2898
	if (rcu_blocking_is_gp())
		return;
2899 2900 2901 2902
	if (rcu_expedited)
		synchronize_rcu_bh_expedited();
	else
		wait_rcu_gp(call_rcu_bh);
2903 2904 2905
}
EXPORT_SYMBOL_GPL(synchronize_rcu_bh);

2906 2907 2908 2909 2910 2911 2912 2913 2914 2915 2916 2917 2918 2919 2920 2921 2922 2923 2924 2925
/**
 * 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().
	 */
2926
	return smp_load_acquire(&rcu_state_p->gpnum);
2927 2928 2929 2930 2931 2932 2933 2934 2935 2936 2937 2938 2939 2940 2941 2942 2943 2944 2945 2946 2947 2948 2949 2950 2951
}
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.
	 */
2952
	newstate = smp_load_acquire(&rcu_state_p->completed);
2953 2954 2955 2956 2957
	if (ULONG_CMP_GE(oldstate, newstate))
		synchronize_rcu();
}
EXPORT_SYMBOL_GPL(cond_synchronize_rcu);

2958 2959 2960 2961 2962 2963 2964 2965 2966 2967 2968 2969 2970 2971 2972 2973 2974
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;
}

2975 2976 2977 2978 2979 2980 2981 2982 2983 2984
/**
 * 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.
2985 2986 2987 2988 2989 2990 2991 2992 2993 2994 2995 2996 2997 2998 2999 3000 3001 3002 3003 3004 3005 3006 3007 3008
 *
 * 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)
{
3009 3010 3011
	cpumask_var_t cm;
	bool cma = false;
	int cpu;
3012 3013
	long firstsnap, s, snap;
	int trycount = 0;
3014
	struct rcu_state *rsp = &rcu_sched_state;
3015

3016 3017 3018 3019 3020 3021 3022 3023
	/*
	 * 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.
	 */
3024 3025
	if (ULONG_CMP_GE((ulong)atomic_long_read(&rsp->expedited_start),
			 (ulong)atomic_long_read(&rsp->expedited_done) +
3026 3027
			 ULONG_MAX / 8)) {
		synchronize_sched();
3028
		atomic_long_inc(&rsp->expedited_wrap);
3029 3030
		return;
	}
3031

3032 3033 3034 3035
	/*
	 * Take a ticket.  Note that atomic_inc_return() implies a
	 * full memory barrier.
	 */
3036
	snap = atomic_long_inc_return(&rsp->expedited_start);
3037
	firstsnap = snap;
3038 3039 3040 3041 3042 3043
	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;
	}
3044
	WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id()));
3045

3046 3047 3048 3049 3050 3051 3052 3053 3054 3055 3056 3057 3058 3059 3060
	/* 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;
	}

3061 3062 3063 3064
	/*
	 * Each pass through the following loop attempts to force a
	 * context switch on each CPU.
	 */
3065
	while (try_stop_cpus(cma ? cm : cpu_online_mask,
3066 3067 3068
			     synchronize_sched_expedited_cpu_stop,
			     NULL) == -EAGAIN) {
		put_online_cpus();
3069
		atomic_long_inc(&rsp->expedited_tryfail);
3070

3071
		/* Check to see if someone else did our work for us. */
3072
		s = atomic_long_read(&rsp->expedited_done);
3073
		if (ULONG_CMP_GE((ulong)s, (ulong)firstsnap)) {
3074
			/* ensure test happens before caller kfree */
3075
			smp_mb__before_atomic(); /* ^^^ */
3076
			atomic_long_inc(&rsp->expedited_workdone1);
3077
			free_cpumask_var(cm);
3078 3079
			return;
		}
3080 3081

		/* No joy, try again later.  Or just synchronize_sched(). */
3082
		if (trycount++ < 10) {
3083
			udelay(trycount * num_online_cpus());
3084
		} else {
3085
			wait_rcu_gp(call_rcu_sched);
3086
			atomic_long_inc(&rsp->expedited_normal);
3087
			free_cpumask_var(cm);
3088 3089 3090
			return;
		}

3091
		/* Recheck to see if someone else did our work for us. */
3092
		s = atomic_long_read(&rsp->expedited_done);
3093
		if (ULONG_CMP_GE((ulong)s, (ulong)firstsnap)) {
3094
			/* ensure test happens before caller kfree */
3095
			smp_mb__before_atomic(); /* ^^^ */
3096
			atomic_long_inc(&rsp->expedited_workdone2);
3097
			free_cpumask_var(cm);
3098 3099 3100 3101 3102
			return;
		}

		/*
		 * Refetching sync_sched_expedited_started allows later
3103 3104 3105 3106
		 * 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.
3107
		 */
3108 3109 3110 3111
		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);
3112
			free_cpumask_var(cm);
3113 3114
			return;
		}
3115
		snap = atomic_long_read(&rsp->expedited_start);
3116 3117
		smp_mb(); /* ensure read is before try_stop_cpus(). */
	}
3118
	atomic_long_inc(&rsp->expedited_stoppedcpus);
3119

3120 3121 3122
all_cpus_idle:
	free_cpumask_var(cm);

3123 3124 3125 3126
	/*
	 * 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
3127
	 * than we did already did their update.
3128 3129
	 */
	do {
3130
		atomic_long_inc(&rsp->expedited_done_tries);
3131
		s = atomic_long_read(&rsp->expedited_done);
3132
		if (ULONG_CMP_GE((ulong)s, (ulong)snap)) {
3133
			/* ensure test happens before caller kfree */
3134
			smp_mb__before_atomic(); /* ^^^ */
3135
			atomic_long_inc(&rsp->expedited_done_lost);
3136 3137
			break;
		}
3138
	} while (atomic_long_cmpxchg(&rsp->expedited_done, s, snap) != s);
3139
	atomic_long_inc(&rsp->expedited_done_exit);
3140 3141 3142 3143 3144

	put_online_cpus();
}
EXPORT_SYMBOL_GPL(synchronize_sched_expedited);

3145 3146 3147 3148 3149 3150 3151 3152 3153
/*
 * 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)
{
3154 3155
	struct rcu_node *rnp = rdp->mynode;

3156 3157 3158 3159 3160
	rdp->n_rcu_pending++;

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

3161 3162 3163 3164
	/* Is this CPU a NO_HZ_FULL CPU that should ignore RCU? */
	if (rcu_nohz_full_cpu(rsp))
		return 0;

3165
	/* Is the RCU core waiting for a quiescent state from this CPU? */
3166 3167
	if (rcu_scheduler_fully_active &&
	    rdp->qs_pending && !rdp->passed_quiesce) {
3168
		rdp->n_rp_qs_pending++;
3169
	} else if (rdp->qs_pending && rdp->passed_quiesce) {
3170
		rdp->n_rp_report_qs++;
3171
		return 1;
3172
	}
3173 3174

	/* Does this CPU have callbacks ready to invoke? */
3175 3176
	if (cpu_has_callbacks_ready_to_invoke(rdp)) {
		rdp->n_rp_cb_ready++;
3177
		return 1;
3178
	}
3179 3180

	/* Has RCU gone idle with this CPU needing another grace period? */
3181 3182
	if (cpu_needs_another_gp(rsp, rdp)) {
		rdp->n_rp_cpu_needs_gp++;
3183
		return 1;
3184
	}
3185 3186

	/* Has another RCU grace period completed?  */
3187
	if (ACCESS_ONCE(rnp->completed) != rdp->completed) { /* outside lock */
3188
		rdp->n_rp_gp_completed++;
3189
		return 1;
3190
	}
3191 3192

	/* Has a new RCU grace period started? */
3193
	if (ACCESS_ONCE(rnp->gpnum) != rdp->gpnum) { /* outside lock */
3194
		rdp->n_rp_gp_started++;
3195
		return 1;
3196
	}
3197

3198 3199 3200 3201 3202 3203
	/* Does this CPU need a deferred NOCB wakeup? */
	if (rcu_nocb_need_deferred_wakeup(rdp)) {
		rdp->n_rp_nocb_defer_wakeup++;
		return 1;
	}

3204
	/* nothing to do */
3205
	rdp->n_rp_need_nothing++;
3206 3207 3208 3209 3210 3211 3212 3213
	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.
 */
3214
static int rcu_pending(void)
3215
{
3216 3217 3218
	struct rcu_state *rsp;

	for_each_rcu_flavor(rsp)
3219
		if (__rcu_pending(rsp, this_cpu_ptr(rsp->rda)))
3220 3221
			return 1;
	return 0;
3222 3223 3224
}

/*
3225 3226 3227
 * 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.)
3228
 */
3229
static int __maybe_unused rcu_cpu_has_callbacks(bool *all_lazy)
3230
{
3231 3232 3233
	bool al = true;
	bool hc = false;
	struct rcu_data *rdp;
3234 3235
	struct rcu_state *rsp;

3236
	for_each_rcu_flavor(rsp) {
3237
		rdp = this_cpu_ptr(rsp->rda);
3238 3239 3240 3241
		if (!rdp->nxtlist)
			continue;
		hc = true;
		if (rdp->qlen != rdp->qlen_lazy || !all_lazy) {
3242
			al = false;
3243 3244
			break;
		}
3245 3246 3247 3248
	}
	if (all_lazy)
		*all_lazy = al;
	return hc;
3249 3250
}

3251 3252 3253 3254
/*
 * Helper function for _rcu_barrier() tracing.  If tracing is disabled,
 * the compiler is expected to optimize this away.
 */
3255
static void _rcu_barrier_trace(struct rcu_state *rsp, const char *s,
3256 3257 3258 3259 3260 3261
			       int cpu, unsigned long done)
{
	trace_rcu_barrier(rsp->name, s, cpu,
			  atomic_read(&rsp->barrier_cpu_count), done);
}

3262 3263 3264 3265
/*
 * RCU callback function for _rcu_barrier().  If we are last, wake
 * up the task executing _rcu_barrier().
 */
3266
static void rcu_barrier_callback(struct rcu_head *rhp)
3267
{
3268 3269 3270
	struct rcu_data *rdp = container_of(rhp, struct rcu_data, barrier_head);
	struct rcu_state *rsp = rdp->rsp;

3271 3272
	if (atomic_dec_and_test(&rsp->barrier_cpu_count)) {
		_rcu_barrier_trace(rsp, "LastCB", -1, rsp->n_barrier_done);
3273
		complete(&rsp->barrier_completion);
3274 3275 3276
	} else {
		_rcu_barrier_trace(rsp, "CB", -1, rsp->n_barrier_done);
	}
3277 3278 3279 3280 3281 3282 3283
}

/*
 * Called with preemption disabled, and from cross-cpu IRQ context.
 */
static void rcu_barrier_func(void *type)
{
3284
	struct rcu_state *rsp = type;
3285
	struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
3286

3287
	_rcu_barrier_trace(rsp, "IRQ", -1, rsp->n_barrier_done);
3288
	atomic_inc(&rsp->barrier_cpu_count);
3289
	rsp->call(&rdp->barrier_head, rcu_barrier_callback);
3290 3291 3292 3293 3294 3295
}

/*
 * Orchestrate the specified type of RCU barrier, waiting for all
 * RCU callbacks of the specified type to complete.
 */
3296
static void _rcu_barrier(struct rcu_state *rsp)
3297
{
3298 3299
	int cpu;
	struct rcu_data *rdp;
3300 3301
	unsigned long snap = ACCESS_ONCE(rsp->n_barrier_done);
	unsigned long snap_done;
3302

3303
	_rcu_barrier_trace(rsp, "Begin", -1, snap);
3304

3305
	/* Take mutex to serialize concurrent rcu_barrier() requests. */
3306
	mutex_lock(&rsp->barrier_mutex);
3307

3308 3309 3310 3311 3312 3313 3314 3315 3316 3317 3318 3319
	/*
	 * 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.
	 */
3320
	snap_done = rsp->n_barrier_done;
3321
	_rcu_barrier_trace(rsp, "Check", -1, snap_done);
3322 3323 3324 3325 3326 3327 3328 3329 3330 3331 3332 3333

	/*
	 * 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)) {
3334
		_rcu_barrier_trace(rsp, "EarlyExit", -1, snap_done);
3335 3336 3337 3338 3339 3340 3341 3342 3343 3344
		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.
	 */
3345
	ACCESS_ONCE(rsp->n_barrier_done) = rsp->n_barrier_done + 1;
3346
	WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 1);
3347
	_rcu_barrier_trace(rsp, "Inc1", -1, rsp->n_barrier_done);
3348
	smp_mb(); /* Order ->n_barrier_done increment with below mechanism. */
3349

3350
	/*
3351 3352
	 * 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
3353 3354
	 * (or preemption of this task).  Exclude CPU-hotplug operations
	 * to ensure that no offline CPU has callbacks queued.
3355
	 */
3356
	init_completion(&rsp->barrier_completion);
3357
	atomic_set(&rsp->barrier_cpu_count, 1);
3358
	get_online_cpus();
3359 3360

	/*
3361 3362 3363
	 * 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.
3364
	 */
P
Paul E. McKenney 已提交
3365
	for_each_possible_cpu(cpu) {
3366
		if (!cpu_online(cpu) && !rcu_is_nocb_cpu(cpu))
P
Paul E. McKenney 已提交
3367
			continue;
3368
		rdp = per_cpu_ptr(rsp->rda, cpu);
3369
		if (rcu_is_nocb_cpu(cpu)) {
3370 3371 3372 3373 3374 3375 3376 3377 3378 3379
			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);
				atomic_inc(&rsp->barrier_cpu_count);
				__call_rcu(&rdp->barrier_head,
					   rcu_barrier_callback, rsp, cpu, 0);
			}
P
Paul E. McKenney 已提交
3380
		} else if (ACCESS_ONCE(rdp->qlen)) {
3381 3382
			_rcu_barrier_trace(rsp, "OnlineQ", cpu,
					   rsp->n_barrier_done);
3383
			smp_call_function_single(cpu, rcu_barrier_func, rsp, 1);
3384
		} else {
3385 3386
			_rcu_barrier_trace(rsp, "OnlineNQ", cpu,
					   rsp->n_barrier_done);
3387 3388
		}
	}
3389
	put_online_cpus();
3390 3391 3392 3393 3394

	/*
	 * Now that we have an rcu_barrier_callback() callback on each
	 * CPU, and thus each counted, remove the initial count.
	 */
3395
	if (atomic_dec_and_test(&rsp->barrier_cpu_count))
3396
		complete(&rsp->barrier_completion);
3397

3398 3399
	/* Increment ->n_barrier_done to prevent duplicate work. */
	smp_mb(); /* Keep increment after above mechanism. */
3400
	ACCESS_ONCE(rsp->n_barrier_done) = rsp->n_barrier_done + 1;
3401
	WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 0);
3402
	_rcu_barrier_trace(rsp, "Inc2", -1, rsp->n_barrier_done);
3403 3404
	smp_mb(); /* Keep increment before caller's subsequent code. */

3405
	/* Wait for all rcu_barrier_callback() callbacks to be invoked. */
3406
	wait_for_completion(&rsp->barrier_completion);
3407 3408

	/* Other rcu_barrier() invocations can now safely proceed. */
3409
	mutex_unlock(&rsp->barrier_mutex);
3410 3411 3412 3413 3414 3415 3416
}

/**
 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
 */
void rcu_barrier_bh(void)
{
3417
	_rcu_barrier(&rcu_bh_state);
3418 3419 3420 3421 3422 3423 3424 3425
}
EXPORT_SYMBOL_GPL(rcu_barrier_bh);

/**
 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
 */
void rcu_barrier_sched(void)
{
3426
	_rcu_barrier(&rcu_sched_state);
3427 3428 3429
}
EXPORT_SYMBOL_GPL(rcu_barrier_sched);

3430
/*
3431
 * Do boot-time initialization of a CPU's per-CPU RCU data.
3432
 */
3433 3434
static void __init
rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
3435 3436
{
	unsigned long flags;
3437
	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
3438 3439 3440
	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
3441
	raw_spin_lock_irqsave(&rnp->lock, flags);
3442
	rdp->grpmask = 1UL << (cpu - rdp->mynode->grplo);
3443
	init_callback_list(rdp);
3444
	rdp->qlen_lazy = 0;
3445
	ACCESS_ONCE(rdp->qlen) = 0;
3446
	rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
3447
	WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE);
3448
	WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1);
3449
	rdp->cpu = cpu;
3450
	rdp->rsp = rsp;
P
Paul E. McKenney 已提交
3451
	rcu_boot_init_nocb_percpu_data(rdp);
P
Paul E. McKenney 已提交
3452
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
3453 3454 3455 3456 3457 3458 3459
}

/*
 * 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.
3460
 */
3461
static void
3462
rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
3463 3464 3465
{
	unsigned long flags;
	unsigned long mask;
3466
	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
3467 3468
	struct rcu_node *rnp = rcu_get_root(rsp);

3469 3470 3471
	/* Exclude new grace periods. */
	mutex_lock(&rsp->onoff_mutex);

3472
	/* Set up local state, ensuring consistent view of global state. */
P
Paul E. McKenney 已提交
3473
	raw_spin_lock_irqsave(&rnp->lock, flags);
3474
	rdp->beenonline = 1;	 /* We have now been online. */
3475 3476
	rdp->qlen_last_fqs_check = 0;
	rdp->n_force_qs_snap = rsp->n_force_qs;
3477
	rdp->blimit = blimit;
3478
	init_callback_list(rdp);  /* Re-enable callbacks on this CPU. */
3479
	rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
3480
	rcu_sysidle_init_percpu_data(rdp->dynticks);
3481 3482
	atomic_set(&rdp->dynticks->dynticks,
		   (atomic_read(&rdp->dynticks->dynticks) & ~0x1) + 1);
P
Paul E. McKenney 已提交
3483
	raw_spin_unlock(&rnp->lock);		/* irqs remain disabled. */
3484 3485 3486 3487 3488 3489

	/* 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
3490
		raw_spin_lock(&rnp->lock);	/* irqs already disabled. */
3491 3492
		rnp->qsmaskinit |= mask;
		mask = rnp->grpmask;
3493
		if (rnp == rdp->mynode) {
3494 3495 3496 3497 3498 3499
			/*
			 * 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;
3500
			rdp->completed = rnp->completed;
3501 3502
			rdp->passed_quiesce = 0;
			rdp->qs_pending = 0;
3503
			trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuonl"));
3504
		}
P
Paul E. McKenney 已提交
3505
		raw_spin_unlock(&rnp->lock); /* irqs already disabled. */
3506 3507
		rnp = rnp->parent;
	} while (rnp != NULL && !(rnp->qsmaskinit & mask));
3508
	local_irq_restore(flags);
3509

3510
	mutex_unlock(&rsp->onoff_mutex);
3511 3512
}

3513
static void rcu_prepare_cpu(int cpu)
3514
{
3515 3516 3517
	struct rcu_state *rsp;

	for_each_rcu_flavor(rsp)
3518
		rcu_init_percpu_data(cpu, rsp);
3519 3520 3521
}

/*
3522
 * Handle CPU online/offline notification events.
3523
 */
3524
static int rcu_cpu_notify(struct notifier_block *self,
3525
				    unsigned long action, void *hcpu)
3526 3527
{
	long cpu = (long)hcpu;
3528
	struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
3529
	struct rcu_node *rnp = rdp->mynode;
3530
	struct rcu_state *rsp;
3531

3532
	trace_rcu_utilization(TPS("Start CPU hotplug"));
3533 3534 3535
	switch (action) {
	case CPU_UP_PREPARE:
	case CPU_UP_PREPARE_FROZEN:
P
Peter Zijlstra 已提交
3536 3537
		rcu_prepare_cpu(cpu);
		rcu_prepare_kthreads(cpu);
3538
		rcu_spawn_all_nocb_kthreads(cpu);
3539 3540
		break;
	case CPU_ONLINE:
3541
	case CPU_DOWN_FAILED:
T
Thomas Gleixner 已提交
3542
		rcu_boost_kthread_setaffinity(rnp, -1);
3543 3544
		break;
	case CPU_DOWN_PREPARE:
3545
		rcu_boost_kthread_setaffinity(rnp, cpu);
3546
		break;
3547 3548
	case CPU_DYING:
	case CPU_DYING_FROZEN:
3549 3550
		for_each_rcu_flavor(rsp)
			rcu_cleanup_dying_cpu(rsp);
3551
		break;
3552 3553 3554 3555
	case CPU_DEAD:
	case CPU_DEAD_FROZEN:
	case CPU_UP_CANCELED:
	case CPU_UP_CANCELED_FROZEN:
3556
		for_each_rcu_flavor(rsp) {
3557
			rcu_cleanup_dead_cpu(cpu, rsp);
3558 3559
			do_nocb_deferred_wakeup(per_cpu_ptr(rsp->rda, cpu));
		}
3560 3561 3562 3563
		break;
	default:
		break;
	}
3564
	trace_rcu_utilization(TPS("End CPU hotplug"));
3565
	return NOTIFY_OK;
3566 3567
}

3568 3569 3570 3571 3572 3573 3574 3575 3576 3577 3578 3579 3580 3581 3582 3583 3584 3585 3586
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;
}

3587
/*
3588
 * Spawn the kthreads that handle each RCU flavor's grace periods.
3589 3590 3591 3592 3593 3594 3595 3596
 */
static int __init rcu_spawn_gp_kthread(void)
{
	unsigned long flags;
	struct rcu_node *rnp;
	struct rcu_state *rsp;
	struct task_struct *t;

3597
	rcu_scheduler_fully_active = 1;
3598
	for_each_rcu_flavor(rsp) {
3599
		t = kthread_run(rcu_gp_kthread, rsp, "%s", rsp->name);
3600 3601 3602 3603 3604 3605
		BUG_ON(IS_ERR(t));
		rnp = rcu_get_root(rsp);
		raw_spin_lock_irqsave(&rnp->lock, flags);
		rsp->gp_kthread = t;
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
	}
3606
	rcu_spawn_nocb_kthreads();
3607
	rcu_spawn_boost_kthreads();
3608 3609 3610 3611
	return 0;
}
early_initcall(rcu_spawn_gp_kthread);

3612 3613 3614 3615 3616 3617 3618 3619 3620 3621 3622 3623 3624 3625 3626
/*
 * 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;
}

3627 3628 3629 3630 3631 3632 3633 3634 3635
/*
 * 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;

3636 3637
	rsp->levelspread[rcu_num_lvls - 1] = rcu_fanout_leaf;
	for (i = rcu_num_lvls - 2; i >= 0; i--)
3638 3639 3640 3641 3642 3643 3644 3645 3646
		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;

3647
	cprv = nr_cpu_ids;
3648
	for (i = rcu_num_lvls - 1; i >= 0; i--) {
3649 3650 3651 3652 3653 3654 3655 3656 3657 3658
		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.
 */
3659 3660
static void __init rcu_init_one(struct rcu_state *rsp,
		struct rcu_data __percpu *rda)
3661
{
3662 3663 3664 3665 3666 3667 3668 3669 3670 3671
	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 */
3672
	static u8 fl_mask = 0x1;
3673 3674 3675 3676 3677
	int cpustride = 1;
	int i;
	int j;
	struct rcu_node *rnp;

3678 3679
	BUILD_BUG_ON(MAX_RCU_LVLS > ARRAY_SIZE(buf));  /* Fix buf[] init! */

3680 3681 3682 3683
	/* 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");

3684 3685
	/* Initialize the level-tracking arrays. */

3686 3687 3688
	for (i = 0; i < rcu_num_lvls; i++)
		rsp->levelcnt[i] = num_rcu_lvl[i];
	for (i = 1; i < rcu_num_lvls; i++)
3689 3690
		rsp->level[i] = rsp->level[i - 1] + rsp->levelcnt[i - 1];
	rcu_init_levelspread(rsp);
3691 3692
	rsp->flavor_mask = fl_mask;
	fl_mask <<= 1;
3693 3694 3695

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

3696
	for (i = rcu_num_lvls - 1; i >= 0; i--) {
3697 3698 3699
		cpustride *= rsp->levelspread[i];
		rnp = rsp->level[i];
		for (j = 0; j < rsp->levelcnt[i]; j++, rnp++) {
P
Paul E. McKenney 已提交
3700
			raw_spin_lock_init(&rnp->lock);
3701 3702
			lockdep_set_class_and_name(&rnp->lock,
						   &rcu_node_class[i], buf[i]);
3703 3704 3705
			raw_spin_lock_init(&rnp->fqslock);
			lockdep_set_class_and_name(&rnp->fqslock,
						   &rcu_fqs_class[i], fqs[i]);
3706 3707
			rnp->gpnum = rsp->gpnum;
			rnp->completed = rsp->completed;
3708 3709 3710 3711
			rnp->qsmask = 0;
			rnp->qsmaskinit = 0;
			rnp->grplo = j * cpustride;
			rnp->grphi = (j + 1) * cpustride - 1;
3712 3713
			if (rnp->grphi >= nr_cpu_ids)
				rnp->grphi = nr_cpu_ids - 1;
3714 3715 3716 3717 3718 3719 3720 3721 3722 3723 3724
			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;
3725
			INIT_LIST_HEAD(&rnp->blkd_tasks);
3726
			rcu_init_one_nocb(rnp);
3727 3728
		}
	}
3729

3730
	rsp->rda = rda;
3731
	init_waitqueue_head(&rsp->gp_wq);
3732
	rnp = rsp->level[rcu_num_lvls - 1];
3733
	for_each_possible_cpu(i) {
3734
		while (i > rnp->grphi)
3735
			rnp++;
3736
		per_cpu_ptr(rsp->rda, i)->mynode = rnp;
3737 3738
		rcu_boot_init_percpu_data(i, rsp);
	}
3739
	list_add(&rsp->flavors, &rcu_struct_flavors);
3740 3741
}

3742 3743
/*
 * Compute the rcu_node tree geometry from kernel parameters.  This cannot
3744
 * replace the definitions in tree.h because those are needed to size
3745 3746 3747 3748
 * the ->node array in the rcu_state structure.
 */
static void __init rcu_init_geometry(void)
{
3749
	ulong d;
3750 3751
	int i;
	int j;
3752
	int n = nr_cpu_ids;
3753 3754
	int rcu_capacity[MAX_RCU_LVLS + 1];

3755 3756 3757 3758 3759 3760 3761 3762 3763 3764 3765 3766 3767
	/*
	 * 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;

3768
	/* If the compile-time values are accurate, just leave. */
3769 3770
	if (rcu_fanout_leaf == CONFIG_RCU_FANOUT_LEAF &&
	    nr_cpu_ids == NR_CPUS)
3771
		return;
3772 3773
	pr_info("RCU: Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%d\n",
		rcu_fanout_leaf, nr_cpu_ids);
3774 3775 3776 3777 3778 3779 3780 3781 3782 3783 3784 3785 3786 3787 3788 3789 3790 3791 3792 3793 3794 3795 3796 3797 3798 3799 3800 3801 3802 3803 3804 3805 3806 3807 3808 3809 3810 3811 3812 3813 3814 3815 3816 3817 3818

	/*
	 * 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;
}

3819
void __init rcu_init(void)
3820
{
P
Paul E. McKenney 已提交
3821
	int cpu;
3822

3823
	rcu_bootup_announce();
3824
	rcu_init_geometry();
3825
	rcu_init_one(&rcu_bh_state, &rcu_bh_data);
3826
	rcu_init_one(&rcu_sched_state, &rcu_sched_data);
3827
	__rcu_init_preempt();
J
Jiang Fang 已提交
3828
	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
3829 3830 3831 3832 3833 3834 3835

	/*
	 * 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);
3836
	pm_notifier(rcu_pm_notify, 0);
P
Paul E. McKenney 已提交
3837 3838
	for_each_online_cpu(cpu)
		rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
3839 3840

	rcu_early_boot_tests();
3841 3842
}

3843
#include "tree_plugin.h"