rcutree.c 78.9 KB
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/*
 * Read-Copy Update mechanism for mutual exclusion
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *
 * 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>
#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 "rcutree.h"
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#include <trace/events/rcu.h>

#include "rcu.h"
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/* Data structures. */

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static struct lock_class_key rcu_node_class[NUM_RCU_LVLS];
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#define RCU_STATE_INITIALIZER(structname) { \
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	.level = { &structname##_state.node[0] }, \
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	.levelcnt = { \
		NUM_RCU_LVL_0,  /* root of hierarchy. */ \
		NUM_RCU_LVL_1, \
		NUM_RCU_LVL_2, \
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		NUM_RCU_LVL_3, \
		NUM_RCU_LVL_4, /* == MAX_RCU_LVLS */ \
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	}, \
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	.fqs_state = RCU_GP_IDLE, \
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	.gpnum = -300, \
	.completed = -300, \
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	.onofflock = __RAW_SPIN_LOCK_UNLOCKED(&structname##_state.onofflock), \
	.fqslock = __RAW_SPIN_LOCK_UNLOCKED(&structname##_state.fqslock), \
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	.n_force_qs = 0, \
	.n_force_qs_ngp = 0, \
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	.name = #structname, \
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}

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struct rcu_state rcu_sched_state = RCU_STATE_INITIALIZER(rcu_sched);
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DEFINE_PER_CPU(struct rcu_data, rcu_sched_data);
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struct rcu_state rcu_bh_state = RCU_STATE_INITIALIZER(rcu_bh);
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DEFINE_PER_CPU(struct rcu_data, rcu_bh_data);
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static struct rcu_state *rcu_state;

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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)
 * optimized synchronize_sched() to a simple barrier().  When this variable
 * 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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#ifdef CONFIG_RCU_BOOST

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/*
 * Control variables for per-CPU and per-rcu_node kthreads.  These
 * handle all flavors of RCU.
 */
static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task);
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DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
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DEFINE_PER_CPU(int, rcu_cpu_kthread_cpu);
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DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
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DEFINE_PER_CPU(char, rcu_cpu_has_work);
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#endif /* #ifdef CONFIG_RCU_BOOST */

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static void rcu_node_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(int cpu)
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{
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	struct rcu_data *rdp = &per_cpu(rcu_sched_data, cpu);
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	rdp->passed_quiesce_gpnum = rdp->gpnum;
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	barrier();
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	if (rdp->passed_quiesce == 0)
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		trace_rcu_grace_period("rcu_sched", rdp->gpnum, "cpuqs");
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	rdp->passed_quiesce = 1;
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}

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void rcu_bh_qs(int cpu)
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{
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	struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu);
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	rdp->passed_quiesce_gpnum = rdp->gpnum;
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	barrier();
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	if (rdp->passed_quiesce == 0)
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		trace_rcu_grace_period("rcu_bh", rdp->gpnum, "cpuqs");
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	rdp->passed_quiesce = 1;
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}
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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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 */
void rcu_note_context_switch(int cpu)
{
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	trace_rcu_utilization("Start context switch");
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	rcu_sched_qs(cpu);
	rcu_preempt_note_context_switch(cpu);
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	trace_rcu_utilization("End context switch");
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}
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EXPORT_SYMBOL_GPL(rcu_note_context_switch);
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DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
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	.dynticks_nesting = DYNTICK_TASK_NESTING,
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	.dynticks = ATOMIC_INIT(1),
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};
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static int blimit = 10;		/* Maximum callbacks per rcu_do_batch. */
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static int qhimark = 10000;	/* If this many pending, ignore blimit. */
static int qlowmark = 100;	/* Once only this many pending, use blimit. */

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module_param(blimit, int, 0);
module_param(qhimark, int, 0);
module_param(qlowmark, int, 0);

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int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */
int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;

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module_param(rcu_cpu_stall_suppress, int, 0644);
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module_param(rcu_cpu_stall_timeout, int, 0644);
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static void force_quiescent_state(struct rcu_state *rsp, int relaxed);
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static int rcu_pending(int cpu);
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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 for RCU BH.
 */
void rcu_bh_force_quiescent_state(void)
{
	force_quiescent_state(&rcu_bh_state, 0);
}
EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state);

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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);

/*
 * 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)
{
	force_quiescent_state(&rcu_sched_state, 0);
}
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)
{
	return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL];
}

/*
 * Does the current CPU require a yet-as-unscheduled grace period?
 */
static int
cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
{
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	return *rdp->nxttail[RCU_DONE_TAIL] && !rcu_gp_in_progress(rsp);
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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];
}

/*
 * If the specified CPU is offline, tell the caller that it is in
 * a quiescent state.  Otherwise, whack it with a reschedule IPI.
 * Grace periods can end up waiting on an offline CPU when that
 * CPU is in the process of coming online -- it will be added to the
 * rcu_node bitmasks before it actually makes it online.  The same thing
 * can happen while a CPU is in the process of coming online.  Because this
 * race is quite rare, we check for it after detecting that the grace
 * period has been delayed rather than checking each and every CPU
 * each and every time we start a new grace period.
 */
static int rcu_implicit_offline_qs(struct rcu_data *rdp)
{
	/*
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	 * If the CPU is offline for more than a jiffy, it is in a quiescent
	 * state.  We can trust its state not to change because interrupts
	 * are disabled.  The reason for the jiffy's worth of slack is to
	 * handle CPUs initializing on the way up and finding their way
	 * to the idle loop on the way down.
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	 */
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	if (cpu_is_offline(rdp->cpu) &&
	    ULONG_CMP_LT(rdp->rsp->gp_start + 2, jiffies)) {
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		trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, "ofl");
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		rdp->offline_fqs++;
		return 1;
	}
	return 0;
}

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/*
 * rcu_idle_enter_common - inform RCU that current CPU is moving towards idle
 *
 * 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_idle_enter_common(struct rcu_dynticks *rdtp, long long oldval)
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{
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	trace_rcu_dyntick("Start", oldval, 0);
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	if (!is_idle_task(current)) {
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		struct task_struct *idle = idle_task(smp_processor_id());

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		trace_rcu_dyntick("Error on entry: not idle task", oldval, 0);
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		ftrace_dump(DUMP_ALL);
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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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	rcu_prepare_for_idle(smp_processor_id());
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	/* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
	smp_mb__before_atomic_inc();  /* See above. */
	atomic_inc(&rdtp->dynticks);
	smp_mb__after_atomic_inc();  /* Force ordering with next sojourn. */
	WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
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	/*
	 * The idle task is not permitted to enter the idle loop while
	 * 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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/**
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 * rcu_idle_enter - inform RCU that current CPU is entering idle
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 *
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 * Enter idle mode, in other words, -leave- the mode in which RCU
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 * read-side critical sections can occur.  (Though RCU read-side
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 * 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.
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 */
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void rcu_idle_enter(void)
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{
	unsigned long flags;
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	long long oldval;
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	struct rcu_dynticks *rdtp;

	local_irq_save(flags);
	rdtp = &__get_cpu_var(rcu_dynticks);
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	oldval = rdtp->dynticks_nesting;
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	rdtp->dynticks_nesting = 0;
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	rcu_idle_enter_common(rdtp, oldval);
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	local_irq_restore(flags);
}

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/**
 * 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.
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 *
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 * 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.
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 */
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void rcu_irq_exit(void)
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{
	unsigned long flags;
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	long long oldval;
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	struct rcu_dynticks *rdtp;

	local_irq_save(flags);
	rdtp = &__get_cpu_var(rcu_dynticks);
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	oldval = rdtp->dynticks_nesting;
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	rdtp->dynticks_nesting--;
	WARN_ON_ONCE(rdtp->dynticks_nesting < 0);
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	if (rdtp->dynticks_nesting)
		trace_rcu_dyntick("--=", oldval, rdtp->dynticks_nesting);
	else
		rcu_idle_enter_common(rdtp, oldval);
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	local_irq_restore(flags);
}

/*
 * rcu_idle_exit_common - inform RCU that current CPU is moving away from idle
 *
 * 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.
 */
static void rcu_idle_exit_common(struct rcu_dynticks *rdtp, long long oldval)
{
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	smp_mb__before_atomic_inc();  /* Force ordering w/previous sojourn. */
	atomic_inc(&rdtp->dynticks);
	/* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
	smp_mb__after_atomic_inc();  /* See above. */
	WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
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	rcu_cleanup_after_idle(smp_processor_id());
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	trace_rcu_dyntick("End", oldval, rdtp->dynticks_nesting);
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	if (!is_idle_task(current)) {
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		struct task_struct *idle = idle_task(smp_processor_id());

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		trace_rcu_dyntick("Error on exit: not idle task",
				  oldval, rdtp->dynticks_nesting);
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		ftrace_dump(DUMP_ALL);
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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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	}
}

/**
 * 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.
 *
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 * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NESTING to
 * allow for the possibility of usermode upcalls messing up our count
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 * of interrupt nesting level during the busy period that is just
 * now starting.
 */
void rcu_idle_exit(void)
{
	unsigned long flags;
	struct rcu_dynticks *rdtp;
	long long oldval;

	local_irq_save(flags);
	rdtp = &__get_cpu_var(rcu_dynticks);
	oldval = rdtp->dynticks_nesting;
	WARN_ON_ONCE(oldval != 0);
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	rdtp->dynticks_nesting = DYNTICK_TASK_NESTING;
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	rcu_idle_exit_common(rdtp, oldval);
	local_irq_restore(flags);
}

/**
 * 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);
	rdtp = &__get_cpu_var(rcu_dynticks);
	oldval = rdtp->dynticks_nesting;
	rdtp->dynticks_nesting++;
	WARN_ON_ONCE(rdtp->dynticks_nesting == 0);
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	if (oldval)
		trace_rcu_dyntick("++=", oldval, rdtp->dynticks_nesting);
	else
		rcu_idle_exit_common(rdtp, oldval);
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	local_irq_restore(flags);
}

/**
 * rcu_nmi_enter - inform RCU of entry to NMI context
 *
 * If the CPU was idle with dynamic ticks active, and there is no
 * irq handler running, this updates rdtp->dynticks_nmi to let the
 * RCU grace-period handling know that the CPU is active.
 */
void rcu_nmi_enter(void)
{
	struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);

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	if (rdtp->dynticks_nmi_nesting == 0 &&
	    (atomic_read(&rdtp->dynticks) & 0x1))
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		return;
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	rdtp->dynticks_nmi_nesting++;
	smp_mb__before_atomic_inc();  /* Force delay from prior write. */
	atomic_inc(&rdtp->dynticks);
	/* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
	smp_mb__after_atomic_inc();  /* See above. */
	WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
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}

/**
 * rcu_nmi_exit - inform RCU of exit from NMI context
 *
 * If the CPU was idle with dynamic ticks active, and there is no
 * irq handler running, this updates rdtp->dynticks_nmi to let the
 * RCU grace-period handling know that the CPU is no longer active.
 */
void rcu_nmi_exit(void)
{
	struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);

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	if (rdtp->dynticks_nmi_nesting == 0 ||
	    --rdtp->dynticks_nmi_nesting != 0)
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		return;
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	/* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
	smp_mb__before_atomic_inc();  /* See above. */
	atomic_inc(&rdtp->dynticks);
	smp_mb__after_atomic_inc();  /* Force delay to next write. */
	WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
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}

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#ifdef CONFIG_PROVE_RCU

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/**
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 * rcu_is_cpu_idle - see if RCU thinks that the current CPU is idle
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 *
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 * If the current CPU is in its idle loop and is neither in an interrupt
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 * or NMI handler, return true.
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 */
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int rcu_is_cpu_idle(void)
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{
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	int ret;

	preempt_disable();
	ret = (atomic_read(&__get_cpu_var(rcu_dynticks).dynticks) & 0x1) == 0;
	preempt_enable();
	return ret;
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}
587
EXPORT_SYMBOL(rcu_is_cpu_idle);
588

589 590 591 592 593 594 595 596
#ifdef CONFIG_HOTPLUG_CPU

/*
 * 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
597 598 599 600 601 602 603 604 605 606 607
 * 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.
608 609 610 611 612 613
 *
 * Disable checking if in an NMI handler because we cannot safely report
 * errors from NMI handlers anyway.
 */
bool rcu_lockdep_current_cpu_online(void)
{
614 615
	struct rcu_data *rdp;
	struct rcu_node *rnp;
616 617 618 619 620
	bool ret;

	if (in_nmi())
		return 1;
	preempt_disable();
621 622 623
	rdp = &__get_cpu_var(rcu_sched_data);
	rnp = rdp->mynode;
	ret = (rdp->grpmask & rnp->qsmaskinit) ||
624 625 626 627 628 629 630 631
	      !rcu_scheduler_fully_active;
	preempt_enable();
	return ret;
}
EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);

#endif /* #ifdef CONFIG_HOTPLUG_CPU */

632 633
#endif /* #ifdef CONFIG_PROVE_RCU */

634
/**
635
 * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle
636
 *
637 638 639
 * 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.
640
 */
641
int rcu_is_cpu_rrupt_from_idle(void)
642
{
643
	return __get_cpu_var(rcu_dynticks).dynticks_nesting <= 1;
644 645 646 647 648
}

/*
 * Snapshot the specified CPU's dynticks counter so that we can later
 * credit them with an implicit quiescent state.  Return 1 if this CPU
649
 * is in dynticks idle mode, which is an extended quiescent state.
650 651 652
 */
static int dyntick_save_progress_counter(struct rcu_data *rdp)
{
653
	rdp->dynticks_snap = atomic_add_return(0, &rdp->dynticks->dynticks);
654
	return (rdp->dynticks_snap & 0x1) == 0;
655 656 657 658 659 660 661 662 663 664
}

/*
 * 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()
 * for this same CPU.
 */
static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
{
665 666
	unsigned int curr;
	unsigned int snap;
667

668 669
	curr = (unsigned int)atomic_add_return(0, &rdp->dynticks->dynticks);
	snap = (unsigned int)rdp->dynticks_snap;
670 671 672 673 674 675 676 677 678

	/*
	 * 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.
	 */
679
	if ((curr & 0x1) == 0 || UINT_CMP_GE(curr, snap + 2)) {
680
		trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, "dti");
681 682 683 684 685 686 687 688
		rdp->dynticks_fqs++;
		return 1;
	}

	/* Go check for the CPU being offline. */
	return rcu_implicit_offline_qs(rdp);
}

689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706
static int jiffies_till_stall_check(void)
{
	int till_stall_check = ACCESS_ONCE(rcu_cpu_stall_timeout);

	/*
	 * Limit check must be consistent with the Kconfig limits
	 * for CONFIG_RCU_CPU_STALL_TIMEOUT.
	 */
	if (till_stall_check < 3) {
		ACCESS_ONCE(rcu_cpu_stall_timeout) = 3;
		till_stall_check = 3;
	} else if (till_stall_check > 300) {
		ACCESS_ONCE(rcu_cpu_stall_timeout) = 300;
		till_stall_check = 300;
	}
	return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;
}

707 708 709
static void record_gp_stall_check_time(struct rcu_state *rsp)
{
	rsp->gp_start = jiffies;
710
	rsp->jiffies_stall = jiffies + jiffies_till_stall_check();
711 712 713 714 715 716 717
}

static void print_other_cpu_stall(struct rcu_state *rsp)
{
	int cpu;
	long delta;
	unsigned long flags;
718
	int ndetected;
719 720 721 722
	struct rcu_node *rnp = rcu_get_root(rsp);

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

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	raw_spin_lock_irqsave(&rnp->lock, flags);
724
	delta = jiffies - rsp->jiffies_stall;
725
	if (delta < RCU_STALL_RAT_DELAY || !rcu_gp_in_progress(rsp)) {
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726
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
727 728
		return;
	}
729
	rsp->jiffies_stall = jiffies + 3 * jiffies_till_stall_check() + 3;
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730
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
731

732 733 734 735 736
	/*
	 * OK, time to rat on our buddy...
	 * See Documentation/RCU/stallwarn.txt for info on how to debug
	 * RCU CPU stall warnings.
	 */
737
	printk(KERN_ERR "INFO: %s detected stalls on CPUs/tasks:",
738
	       rsp->name);
739
	print_cpu_stall_info_begin();
740
	rcu_for_each_leaf_node(rsp, rnp) {
741
		raw_spin_lock_irqsave(&rnp->lock, flags);
742
		ndetected += rcu_print_task_stall(rnp);
743
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
744
		if (rnp->qsmask == 0)
745
			continue;
746
		for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
747
			if (rnp->qsmask & (1UL << cpu)) {
748
				print_cpu_stall_info(rsp, rnp->grplo + cpu);
749 750
				ndetected++;
			}
751
	}
752 753 754 755 756 757 758 759 760 761 762 763

	/*
	 * 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);
	ndetected = rcu_print_task_stall(rnp);
	raw_spin_unlock_irqrestore(&rnp->lock, flags);

	print_cpu_stall_info_end();
	printk(KERN_CONT "(detected by %d, t=%ld jiffies)\n",
764
	       smp_processor_id(), (long)(jiffies - rsp->gp_start));
765 766 767
	if (ndetected == 0)
		printk(KERN_ERR "INFO: Stall ended before state dump start\n");
	else if (!trigger_all_cpu_backtrace())
768
		dump_stack();
769

770 771 772 773
	/* If so configured, complain about tasks blocking the grace period. */

	rcu_print_detail_task_stall(rsp);

774 775 776 777 778 779 780 781
	force_quiescent_state(rsp, 0);  /* Kick them all. */
}

static void print_cpu_stall(struct rcu_state *rsp)
{
	unsigned long flags;
	struct rcu_node *rnp = rcu_get_root(rsp);

782 783 784 785 786
	/*
	 * OK, time to rat on ourselves...
	 * See Documentation/RCU/stallwarn.txt for info on how to debug
	 * RCU CPU stall warnings.
	 */
787 788 789 790 791
	printk(KERN_ERR "INFO: %s self-detected stall on CPU", rsp->name);
	print_cpu_stall_info_begin();
	print_cpu_stall_info(rsp, smp_processor_id());
	print_cpu_stall_info_end();
	printk(KERN_CONT " (t=%lu jiffies)\n", jiffies - rsp->gp_start);
792 793
	if (!trigger_all_cpu_backtrace())
		dump_stack();
794

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795
	raw_spin_lock_irqsave(&rnp->lock, flags);
796
	if (ULONG_CMP_GE(jiffies, rsp->jiffies_stall))
797 798
		rsp->jiffies_stall = jiffies +
				     3 * jiffies_till_stall_check() + 3;
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	raw_spin_unlock_irqrestore(&rnp->lock, flags);
800

801 802 803 804 805
	set_need_resched();  /* kick ourselves to get things going. */
}

static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
{
806 807
	unsigned long j;
	unsigned long js;
808 809
	struct rcu_node *rnp;

810
	if (rcu_cpu_stall_suppress)
811
		return;
812 813
	j = ACCESS_ONCE(jiffies);
	js = ACCESS_ONCE(rsp->jiffies_stall);
814
	rnp = rdp->mynode;
815
	if ((ACCESS_ONCE(rnp->qsmask) & rdp->grpmask) && ULONG_CMP_GE(j, js)) {
816 817 818 819

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

820 821
	} else if (rcu_gp_in_progress(rsp) &&
		   ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY)) {
822

823
		/* They had a few time units to dump stack, so complain. */
824 825 826 827
		print_other_cpu_stall(rsp);
	}
}

828 829
static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
{
830
	rcu_cpu_stall_suppress = 1;
831 832 833
	return NOTIFY_DONE;
}

834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849
/**
 * 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)
{
	rcu_sched_state.jiffies_stall = jiffies + ULONG_MAX / 2;
	rcu_bh_state.jiffies_stall = jiffies + ULONG_MAX / 2;
	rcu_preempt_stall_reset();
}

850 851 852 853 854 855 856 857 858
static struct notifier_block rcu_panic_block = {
	.notifier_call = rcu_panic,
};

static void __init check_cpu_stall_init(void)
{
	atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
}

859 860 861
/*
 * Update CPU-local rcu_data state to record the newly noticed grace period.
 * This is used both when we started the grace period and when we notice
862 863 864
 * that someone else started the grace period.  The caller must hold the
 * ->lock of the leaf rcu_node structure corresponding to the current CPU,
 *  and must have irqs disabled.
865
 */
866 867 868
static void __note_new_gpnum(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
{
	if (rdp->gpnum != rnp->gpnum) {
869 870 871 872 873
		/*
		 * If the current grace period is waiting for this CPU,
		 * set up to detect a quiescent state, otherwise don't
		 * go looking for one.
		 */
874
		rdp->gpnum = rnp->gpnum;
875
		trace_rcu_grace_period(rsp->name, rdp->gpnum, "cpustart");
876 877
		if (rnp->qsmask & rdp->grpmask) {
			rdp->qs_pending = 1;
878
			rdp->passed_quiesce = 0;
879 880
		} else
			rdp->qs_pending = 0;
881
		zero_cpu_stall_ticks(rdp);
882 883 884
	}
}

885 886
static void note_new_gpnum(struct rcu_state *rsp, struct rcu_data *rdp)
{
887 888 889 890 891 892
	unsigned long flags;
	struct rcu_node *rnp;

	local_irq_save(flags);
	rnp = rdp->mynode;
	if (rdp->gpnum == ACCESS_ONCE(rnp->gpnum) || /* outside lock. */
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	    !raw_spin_trylock(&rnp->lock)) { /* irqs already off, so later. */
894 895 896 897
		local_irq_restore(flags);
		return;
	}
	__note_new_gpnum(rsp, rnp, rdp);
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898
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920
}

/*
 * Did someone else start a new RCU grace period start since we last
 * checked?  Update local state appropriately if so.  Must be called
 * on the CPU corresponding to rdp.
 */
static int
check_for_new_grace_period(struct rcu_state *rsp, struct rcu_data *rdp)
{
	unsigned long flags;
	int ret = 0;

	local_irq_save(flags);
	if (rdp->gpnum != rsp->gpnum) {
		note_new_gpnum(rsp, rdp);
		ret = 1;
	}
	local_irq_restore(flags);
	return ret;
}

921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939
/*
 * Advance this CPU's callbacks, but only if the current grace period
 * has ended.  This may be called only from the CPU to whom the rdp
 * belongs.  In addition, the corresponding leaf rcu_node structure's
 * ->lock must be held by the caller, with irqs disabled.
 */
static void
__rcu_process_gp_end(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
{
	/* Did another grace period end? */
	if (rdp->completed != rnp->completed) {

		/* Advance callbacks.  No harm if list empty. */
		rdp->nxttail[RCU_DONE_TAIL] = rdp->nxttail[RCU_WAIT_TAIL];
		rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_READY_TAIL];
		rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];

		/* Remember that we saw this grace-period completion. */
		rdp->completed = rnp->completed;
940
		trace_rcu_grace_period(rsp->name, rdp->gpnum, "cpuend");
941

942 943
		/*
		 * If we were in an extended quiescent state, we may have
944
		 * missed some grace periods that others CPUs handled on
945
		 * our behalf. Catch up with this state to avoid noting
946 947 948
		 * spurious new grace periods.  If another grace period
		 * has started, then rnp->gpnum will have advanced, so
		 * we will detect this later on.
949
		 */
950
		if (ULONG_CMP_LT(rdp->gpnum, rdp->completed))
951 952
			rdp->gpnum = rdp->completed;

953
		/*
954 955
		 * If RCU does not need a quiescent state from this CPU,
		 * then make sure that this CPU doesn't go looking for one.
956
		 */
957
		if ((rnp->qsmask & rdp->grpmask) == 0)
958
			rdp->qs_pending = 0;
959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975
	}
}

/*
 * Advance this CPU's callbacks, but only if the current grace period
 * has ended.  This may be called only from the CPU to whom the rdp
 * belongs.
 */
static void
rcu_process_gp_end(struct rcu_state *rsp, struct rcu_data *rdp)
{
	unsigned long flags;
	struct rcu_node *rnp;

	local_irq_save(flags);
	rnp = rdp->mynode;
	if (rdp->completed == ACCESS_ONCE(rnp->completed) || /* outside lock. */
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976
	    !raw_spin_trylock(&rnp->lock)) { /* irqs already off, so later. */
977 978 979 980
		local_irq_restore(flags);
		return;
	}
	__rcu_process_gp_end(rsp, rnp, rdp);
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981
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007
}

/*
 * Do per-CPU grace-period initialization for running CPU.  The caller
 * must hold the lock of the leaf rcu_node structure corresponding to
 * this CPU.
 */
static void
rcu_start_gp_per_cpu(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
{
	/* Prior grace period ended, so advance callbacks for current CPU. */
	__rcu_process_gp_end(rsp, rnp, rdp);

	/*
	 * Because this CPU just now started the new grace period, we know
	 * that all of its callbacks will be covered by this upcoming grace
	 * period, even the ones that were registered arbitrarily recently.
	 * Therefore, advance all outstanding callbacks to RCU_WAIT_TAIL.
	 *
	 * Other CPUs cannot be sure exactly when the grace period started.
	 * Therefore, their recently registered callbacks must pass through
	 * an additional RCU_NEXT_READY stage, so that they will be handled
	 * by the next RCU grace period.
	 */
	rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
	rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
1008 1009 1010

	/* Set state so that this CPU will detect the next quiescent state. */
	__note_new_gpnum(rsp, rnp, rdp);
1011 1012
}

1013 1014 1015 1016 1017
/*
 * Start a new RCU grace period if warranted, re-initializing the hierarchy
 * in preparation for detecting the next grace period.  The caller must hold
 * the root node's ->lock, which is released before return.  Hard irqs must
 * be disabled.
1018 1019 1020 1021
 *
 * 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.
1022 1023 1024 1025 1026
 */
static void
rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
	__releases(rcu_get_root(rsp)->lock)
{
1027
	struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
1028 1029
	struct rcu_node *rnp = rcu_get_root(rsp);

1030
	if (!rcu_scheduler_fully_active ||
1031 1032 1033 1034 1035 1036 1037 1038 1039 1040
	    !cpu_needs_another_gp(rsp, rdp)) {
		/*
		 * Either the scheduler hasn't yet spawned the first
		 * non-idle task or this CPU does not need another
		 * grace period.  Either way, don't start a new grace
		 * period.
		 */
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
		return;
	}
1041

1042
	if (rsp->fqs_active) {
1043
		/*
1044 1045
		 * This CPU needs a grace period, but force_quiescent_state()
		 * is running.  Tell it to start one on this CPU's behalf.
1046
		 */
1047 1048
		rsp->fqs_need_gp = 1;
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
1049 1050 1051 1052 1053
		return;
	}

	/* Advance to a new grace period and initialize state. */
	rsp->gpnum++;
1054
	trace_rcu_grace_period(rsp->name, rsp->gpnum, "start");
1055 1056
	WARN_ON_ONCE(rsp->fqs_state == RCU_GP_INIT);
	rsp->fqs_state = RCU_GP_INIT; /* Hold off force_quiescent_state. */
1057 1058
	rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
	record_gp_stall_check_time(rsp);
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	raw_spin_unlock(&rnp->lock);  /* leave irqs disabled. */
1060 1061

	/* Exclude any concurrent CPU-hotplug operations. */
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1062
	raw_spin_lock(&rsp->onofflock);  /* irqs already disabled. */
1063 1064

	/*
1065 1066 1067 1068 1069 1070 1071 1072 1073
	 * 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.  This
	 * operation relies on the layout of the hierarchy within the
	 * rsp->node[] array.  Note that other CPUs will access only
	 * the leaves of the hierarchy, which still indicate 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.
1074 1075 1076 1077
	 *
	 * Note that the grace period cannot complete until we finish
	 * the initialization process, as there will be at least one
	 * qsmask bit set in the root node until that time, namely the
1078 1079
	 * one corresponding to this CPU, due to the fact that we have
	 * irqs disabled.
1080
	 */
1081
	rcu_for_each_node_breadth_first(rsp, rnp) {
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1082
		raw_spin_lock(&rnp->lock);	/* irqs already disabled. */
1083
		rcu_preempt_check_blocked_tasks(rnp);
1084
		rnp->qsmask = rnp->qsmaskinit;
1085
		rnp->gpnum = rsp->gpnum;
1086 1087 1088
		rnp->completed = rsp->completed;
		if (rnp == rdp->mynode)
			rcu_start_gp_per_cpu(rsp, rnp, rdp);
1089
		rcu_preempt_boost_start_gp(rnp);
1090 1091 1092
		trace_rcu_grace_period_init(rsp->name, rnp->gpnum,
					    rnp->level, rnp->grplo,
					    rnp->grphi, rnp->qsmask);
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1093
		raw_spin_unlock(&rnp->lock);	/* irqs remain disabled. */
1094 1095
	}

1096
	rnp = rcu_get_root(rsp);
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1097
	raw_spin_lock(&rnp->lock);		/* irqs already disabled. */
1098
	rsp->fqs_state = RCU_SIGNAL_INIT; /* force_quiescent_state now OK. */
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1099 1100
	raw_spin_unlock(&rnp->lock);		/* irqs remain disabled. */
	raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
1101 1102
}

1103
/*
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1104 1105 1106 1107 1108
 * 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
 * if one is needed.  Note that the caller must hold rnp->lock, as
 * required by rcu_start_gp(), which will release it.
1109
 */
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1110
static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
1111
	__releases(rcu_get_root(rsp)->lock)
1112
{
1113
	unsigned long gp_duration;
1114 1115
	struct rcu_node *rnp = rcu_get_root(rsp);
	struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
1116

1117
	WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
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Paul E. McKenney 已提交
1118 1119 1120 1121 1122 1123

	/*
	 * Ensure that all grace-period and pre-grace-period activity
	 * is seen before the assignment to rsp->completed.
	 */
	smp_mb(); /* See above block comment. */
1124 1125 1126
	gp_duration = jiffies - rsp->gp_start;
	if (gp_duration > rsp->gp_max)
		rsp->gp_max = gp_duration;
1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160

	/*
	 * 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.
	 *
	 * But if this CPU needs another grace period, it will take
	 * care of this while initializing the next grace period.
	 * We use RCU_WAIT_TAIL instead of the usual RCU_DONE_TAIL
	 * because the callbacks have not yet been advanced: Those
	 * callbacks are waiting on the grace period that just now
	 * completed.
	 */
	if (*rdp->nxttail[RCU_WAIT_TAIL] == NULL) {
		raw_spin_unlock(&rnp->lock);	 /* irqs remain disabled. */

		/*
		 * 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.
		 */
		rcu_for_each_node_breadth_first(rsp, rnp) {
			raw_spin_lock(&rnp->lock); /* irqs already disabled. */
			rnp->completed = rsp->gpnum;
			raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
		}
		rnp = rcu_get_root(rsp);
		raw_spin_lock(&rnp->lock); /* irqs already disabled. */
	}

	rsp->completed = rsp->gpnum;  /* Declare the grace period complete. */
1161
	trace_rcu_grace_period(rsp->name, rsp->completed, "end");
1162
	rsp->fqs_state = RCU_GP_IDLE;
1163 1164 1165
	rcu_start_gp(rsp, flags);  /* releases root node's rnp->lock. */
}

1166
/*
P
Paul E. McKenney 已提交
1167 1168 1169 1170 1171 1172
 * 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.
1173 1174
 */
static void
P
Paul E. McKenney 已提交
1175 1176
rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
		  struct rcu_node *rnp, unsigned long flags)
1177 1178
	__releases(rnp->lock)
{
1179 1180
	struct rcu_node *rnp_c;

1181 1182 1183 1184 1185
	/* 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
1186
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
1187 1188 1189
			return;
		}
		rnp->qsmask &= ~mask;
1190 1191 1192 1193
		trace_rcu_quiescent_state_report(rsp->name, rnp->gpnum,
						 mask, rnp->qsmask, rnp->level,
						 rnp->grplo, rnp->grphi,
						 !!rnp->gp_tasks);
1194
		if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
1195 1196

			/* Other bits still set at this level, so done. */
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Paul E. McKenney 已提交
1197
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
1198 1199 1200 1201 1202 1203 1204 1205 1206
			return;
		}
		mask = rnp->grpmask;
		if (rnp->parent == NULL) {

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

			break;
		}
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Paul E. McKenney 已提交
1207
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
1208
		rnp_c = rnp;
1209
		rnp = rnp->parent;
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Paul E. McKenney 已提交
1210
		raw_spin_lock_irqsave(&rnp->lock, flags);
1211
		WARN_ON_ONCE(rnp_c->qsmask);
1212 1213 1214 1215
	}

	/*
	 * Get here if we are the last CPU to pass through a quiescent
P
Paul E. McKenney 已提交
1216
	 * state for this grace period.  Invoke rcu_report_qs_rsp()
1217
	 * to clean up and start the next grace period if one is needed.
1218
	 */
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Paul E. McKenney 已提交
1219
	rcu_report_qs_rsp(rsp, flags); /* releases rnp->lock. */
1220 1221 1222
}

/*
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Paul E. McKenney 已提交
1223 1224 1225 1226 1227 1228 1229
 * 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!
1230 1231
 */
static void
1232
rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp, long lastgp)
1233 1234 1235 1236 1237 1238
{
	unsigned long flags;
	unsigned long mask;
	struct rcu_node *rnp;

	rnp = rdp->mynode;
P
Paul E. McKenney 已提交
1239
	raw_spin_lock_irqsave(&rnp->lock, flags);
1240
	if (lastgp != rnp->gpnum || rnp->completed == rnp->gpnum) {
1241 1242

		/*
1243 1244 1245 1246
		 * 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.
1247
		 */
1248
		rdp->passed_quiesce = 0;	/* need qs for new gp. */
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Paul E. McKenney 已提交
1249
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
1250 1251 1252 1253
		return;
	}
	mask = rdp->grpmask;
	if ((rnp->qsmask & mask) == 0) {
P
Paul E. McKenney 已提交
1254
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
1255 1256 1257 1258 1259 1260 1261 1262 1263
	} 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.
		 */
		rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];

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Paul E. McKenney 已提交
1264
		rcu_report_qs_rnp(mask, rsp, rnp, flags); /* rlses rnp->lock */
1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291
	}
}

/*
 * 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)
{
	/* If there is now a new grace period, record and return. */
	if (check_for_new_grace_period(rsp, rdp))
		return;

	/*
	 * 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.
	 */
1292
	if (!rdp->passed_quiesce)
1293 1294
		return;

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Paul E. McKenney 已提交
1295 1296 1297 1298
	/*
	 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
	 * judge of that).
	 */
1299
	rcu_report_qs_rdp(rdp->cpu, rsp, rdp, rdp->passed_quiesce_gpnum);
1300 1301 1302 1303
}

#ifdef CONFIG_HOTPLUG_CPU

1304
/*
1305
 * Move a dying CPU's RCU callbacks to online CPU's callback list.
1306 1307 1308 1309 1310 1311 1312 1313 1314
 * Also record a quiescent state for this CPU for the current grace period.
 * Synchronization and interrupt disabling are not required because
 * this function executes in stop_machine() context.  Therefore, cleanup
 * operations that might block must be done later from the CPU_DEAD
 * notifier.
 *
 * Note that the outgoing CPU's bit has already been cleared in the
 * cpu_online_mask.  This allows us to randomly pick a callback
 * destination from the bits set in that mask.
1315
 */
1316
static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
1317 1318
{
	int i;
1319
	unsigned long mask;
1320
	int receive_cpu = cpumask_any(cpu_online_mask);
1321
	struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
1322
	struct rcu_data *receive_rdp = per_cpu_ptr(rsp->rda, receive_cpu);
1323
	RCU_TRACE(struct rcu_node *rnp = rdp->mynode); /* For dying CPU. */
1324

1325 1326 1327 1328 1329 1330 1331 1332 1333 1334 1335 1336 1337 1338 1339 1340 1341 1342 1343 1344 1345 1346 1347 1348 1349 1350 1351 1352 1353 1354 1355 1356 1357 1358 1359 1360 1361 1362 1363 1364
	/* First, adjust the counts. */
	if (rdp->nxtlist != NULL) {
		receive_rdp->qlen_lazy += rdp->qlen_lazy;
		receive_rdp->qlen += rdp->qlen;
		rdp->qlen_lazy = 0;
		rdp->qlen = 0;
	}

	/*
	 * Next, move ready-to-invoke callbacks to be invoked on some
	 * other CPU.  These will not be required to pass through another
	 * grace period:  They are done, regardless of CPU.
	 */
	if (rdp->nxtlist != NULL &&
	    rdp->nxttail[RCU_DONE_TAIL] != &rdp->nxtlist) {
		struct rcu_head *oldhead;
		struct rcu_head **oldtail;
		struct rcu_head **newtail;

		oldhead = rdp->nxtlist;
		oldtail = receive_rdp->nxttail[RCU_DONE_TAIL];
		rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
		*rdp->nxttail[RCU_DONE_TAIL] = *oldtail;
		*receive_rdp->nxttail[RCU_DONE_TAIL] = oldhead;
		newtail = rdp->nxttail[RCU_DONE_TAIL];
		for (i = RCU_DONE_TAIL; i < RCU_NEXT_SIZE; i++) {
			if (receive_rdp->nxttail[i] == oldtail)
				receive_rdp->nxttail[i] = newtail;
			if (rdp->nxttail[i] == newtail)
				rdp->nxttail[i] = &rdp->nxtlist;
		}
	}

	/*
	 * Finally, put the rest of the callbacks at the end of the list.
	 * The ones that made it partway through get to start over:  We
	 * cannot assume that grace periods are synchronized across CPUs.
	 * (We could splice RCU_WAIT_TAIL into RCU_NEXT_READY_TAIL, but
	 * this does not seem compelling.  Not yet, anyway.)
	 */
1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375
	if (rdp->nxtlist != NULL) {
		*receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxtlist;
		receive_rdp->nxttail[RCU_NEXT_TAIL] =
				rdp->nxttail[RCU_NEXT_TAIL];
		receive_rdp->n_cbs_adopted += rdp->qlen;
		rdp->n_cbs_orphaned += rdp->qlen;

		rdp->nxtlist = NULL;
		for (i = 0; i < RCU_NEXT_SIZE; i++)
			rdp->nxttail[i] = &rdp->nxtlist;
	}
1376

1377 1378 1379 1380 1381 1382
	/*
	 * Record a quiescent state for the dying CPU.  This is safe
	 * only because we have already cleared out the callbacks.
	 * (Otherwise, the RCU core might try to schedule the invocation
	 * of callbacks on this now-offline CPU, which would be bad.)
	 */
1383
	mask = rdp->grpmask;	/* rnp->grplo is constant. */
1384 1385 1386 1387 1388
	trace_rcu_grace_period(rsp->name,
			       rnp->gpnum + 1 - !!(rnp->qsmask & mask),
			       "cpuofl");
	rcu_report_qs_rdp(smp_processor_id(), rsp, rdp, rsp->gpnum);
	/* Note that rcu_report_qs_rdp() might call trace_rcu_grace_period(). */
1389 1390 1391
}

/*
1392 1393 1394 1395
 * The CPU has been completely removed, and some other CPU is reporting
 * this fact from process context.  Do the remainder of the cleanup.
 * There can only be one CPU hotplug operation at a time, so no other
 * CPU can be attempting to update rcu_cpu_kthread_task.
1396
 */
1397
static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
1398
{
1399 1400 1401
	unsigned long flags;
	unsigned long mask;
	int need_report = 0;
1402
	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
1403
	struct rcu_node *rnp = rdp->mynode;  /* Outgoing CPU's rnp. */
1404

1405
	/* Adjust any no-longer-needed kthreads. */
1406 1407
	rcu_stop_cpu_kthread(cpu);
	rcu_node_kthread_setaffinity(rnp, -1);
1408 1409 1410 1411 1412 1413 1414 1415 1416 1417 1418 1419 1420 1421 1422 1423 1424 1425 1426 1427 1428 1429 1430 1431 1432 1433 1434 1435 1436 1437 1438 1439 1440 1441 1442 1443 1444 1445

	/* Remove the dying CPU from the bitmasks in the rcu_node hierarchy. */

	/* Exclude any attempts to start a new grace period. */
	raw_spin_lock_irqsave(&rsp->onofflock, flags);

	/* 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. */
		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
	 * because invoking rcu_report_unblock_qs_rnp() with ->onofflock
	 * held leads to deadlock.
	 */
	raw_spin_unlock(&rsp->onofflock); /* irqs remain disabled. */
	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);
1446 1447 1448 1449
}

#else /* #ifdef CONFIG_HOTPLUG_CPU */

1450
static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
1451 1452 1453
{
}

1454
static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
1455 1456 1457 1458 1459 1460 1461 1462 1463
{
}

#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.
 */
1464
static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
1465 1466 1467
{
	unsigned long flags;
	struct rcu_head *next, *list, **tail;
1468
	int bl, count, count_lazy;
1469 1470

	/* If no callbacks are ready, just return.*/
1471
	if (!cpu_has_callbacks_ready_to_invoke(rdp)) {
1472
		trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, 0);
1473 1474 1475
		trace_rcu_batch_end(rsp->name, 0, !!ACCESS_ONCE(rdp->nxtlist),
				    need_resched(), is_idle_task(current),
				    rcu_is_callbacks_kthread());
1476
		return;
1477
	}
1478 1479 1480 1481 1482 1483

	/*
	 * Extract the list of ready callbacks, disabling to prevent
	 * races with call_rcu() from interrupt handlers.
	 */
	local_irq_save(flags);
1484
	WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
1485
	bl = rdp->blimit;
1486
	trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, bl);
1487 1488 1489 1490 1491 1492 1493 1494 1495 1496
	list = rdp->nxtlist;
	rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
	*rdp->nxttail[RCU_DONE_TAIL] = NULL;
	tail = rdp->nxttail[RCU_DONE_TAIL];
	for (count = RCU_NEXT_SIZE - 1; count >= 0; count--)
		if (rdp->nxttail[count] == rdp->nxttail[RCU_DONE_TAIL])
			rdp->nxttail[count] = &rdp->nxtlist;
	local_irq_restore(flags);

	/* Invoke callbacks. */
1497
	count = count_lazy = 0;
1498 1499 1500
	while (list) {
		next = list->next;
		prefetch(next);
1501
		debug_rcu_head_unqueue(list);
1502 1503
		if (__rcu_reclaim(rsp->name, list))
			count_lazy++;
1504
		list = next;
1505 1506 1507 1508
		/* Stop only if limit reached and CPU has something to do. */
		if (++count >= bl &&
		    (need_resched() ||
		     (!is_idle_task(current) && !rcu_is_callbacks_kthread())))
1509 1510 1511 1512
			break;
	}

	local_irq_save(flags);
1513 1514 1515
	trace_rcu_batch_end(rsp->name, count, !!list, need_resched(),
			    is_idle_task(current),
			    rcu_is_callbacks_kthread());
1516 1517

	/* Update count, and requeue any remaining callbacks. */
1518
	rdp->qlen_lazy -= count_lazy;
1519
	rdp->qlen -= count;
1520
	rdp->n_cbs_invoked += count;
1521 1522 1523 1524 1525 1526 1527 1528 1529 1530 1531 1532 1533 1534
	if (list != NULL) {
		*tail = rdp->nxtlist;
		rdp->nxtlist = list;
		for (count = 0; count < RCU_NEXT_SIZE; count++)
			if (&rdp->nxtlist == rdp->nxttail[count])
				rdp->nxttail[count] = tail;
			else
				break;
	}

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

1535 1536 1537 1538 1539 1540 1541
	/* 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;

1542 1543
	local_irq_restore(flags);

1544
	/* Re-invoke RCU core processing if there are callbacks remaining. */
1545
	if (cpu_has_callbacks_ready_to_invoke(rdp))
1546
		invoke_rcu_core();
1547 1548 1549 1550 1551
}

/*
 * 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).
1552
 * Also schedule RCU core processing.
1553
 *
1554
 * This function must be called from hardirq context.  It is normally
1555 1556 1557 1558 1559
 * invoked from the scheduling-clock interrupt.  If rcu_pending returns
 * false, there is no point in invoking rcu_check_callbacks().
 */
void rcu_check_callbacks(int cpu, int user)
{
1560
	trace_rcu_utilization("Start scheduler-tick");
1561
	increment_cpu_stall_ticks();
1562
	if (user || rcu_is_cpu_rrupt_from_idle()) {
1563 1564 1565 1566 1567

		/*
		 * 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
1568
		 * a quiescent state, so note it.
1569 1570
		 *
		 * No memory barrier is required here because both
1571 1572 1573
		 * 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.
1574 1575
		 */

1576 1577
		rcu_sched_qs(cpu);
		rcu_bh_qs(cpu);
1578 1579 1580 1581 1582 1583 1584

	} 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
1585
		 * critical section, so note it.
1586 1587
		 */

1588
		rcu_bh_qs(cpu);
1589
	}
1590
	rcu_preempt_check_callbacks(cpu);
1591
	if (rcu_pending(cpu))
1592
		invoke_rcu_core();
1593
	trace_rcu_utilization("End scheduler-tick");
1594 1595 1596 1597 1598
}

/*
 * Scan the leaf rcu_node structures, processing dyntick state for any that
 * have not yet encountered a quiescent state, using the function specified.
1599 1600
 * Also initiate boosting for any threads blocked on the root rcu_node.
 *
1601
 * The caller must have suppressed start of new grace periods.
1602
 */
1603
static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *))
1604 1605 1606 1607 1608
{
	unsigned long bit;
	int cpu;
	unsigned long flags;
	unsigned long mask;
1609
	struct rcu_node *rnp;
1610

1611
	rcu_for_each_leaf_node(rsp, rnp) {
1612
		mask = 0;
P
Paul E. McKenney 已提交
1613
		raw_spin_lock_irqsave(&rnp->lock, flags);
1614
		if (!rcu_gp_in_progress(rsp)) {
P
Paul E. McKenney 已提交
1615
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
1616
			return;
1617
		}
1618
		if (rnp->qsmask == 0) {
1619
			rcu_initiate_boost(rnp, flags); /* releases rnp->lock */
1620 1621
			continue;
		}
1622
		cpu = rnp->grplo;
1623
		bit = 1;
1624
		for (; cpu <= rnp->grphi; cpu++, bit <<= 1) {
1625 1626
			if ((rnp->qsmask & bit) != 0 &&
			    f(per_cpu_ptr(rsp->rda, cpu)))
1627 1628
				mask |= bit;
		}
1629
		if (mask != 0) {
1630

P
Paul E. McKenney 已提交
1631 1632
			/* rcu_report_qs_rnp() releases rnp->lock. */
			rcu_report_qs_rnp(mask, rsp, rnp, flags);
1633 1634
			continue;
		}
P
Paul E. McKenney 已提交
1635
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
1636
	}
1637
	rnp = rcu_get_root(rsp);
1638 1639 1640 1641
	if (rnp->qsmask == 0) {
		raw_spin_lock_irqsave(&rnp->lock, flags);
		rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */
	}
1642 1643 1644 1645 1646 1647 1648 1649 1650 1651 1652
}

/*
 * Force quiescent states on reluctant CPUs, and also detect which
 * CPUs are in dyntick-idle mode.
 */
static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
{
	unsigned long flags;
	struct rcu_node *rnp = rcu_get_root(rsp);

1653 1654 1655
	trace_rcu_utilization("Start fqs");
	if (!rcu_gp_in_progress(rsp)) {
		trace_rcu_utilization("End fqs");
1656
		return;  /* No grace period in progress, nothing to force. */
1657
	}
P
Paul E. McKenney 已提交
1658
	if (!raw_spin_trylock_irqsave(&rsp->fqslock, flags)) {
1659
		rsp->n_force_qs_lh++; /* Inexact, can lose counts.  Tough! */
1660
		trace_rcu_utilization("End fqs");
1661 1662
		return;	/* Someone else is already on the job. */
	}
1663
	if (relaxed && ULONG_CMP_GE(rsp->jiffies_force_qs, jiffies))
1664
		goto unlock_fqs_ret; /* no emergency and done recently. */
1665
	rsp->n_force_qs++;
P
Paul E. McKenney 已提交
1666
	raw_spin_lock(&rnp->lock);  /* irqs already disabled */
1667
	rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
1668
	if(!rcu_gp_in_progress(rsp)) {
1669
		rsp->n_force_qs_ngp++;
P
Paul E. McKenney 已提交
1670
		raw_spin_unlock(&rnp->lock);  /* irqs remain disabled */
1671
		goto unlock_fqs_ret;  /* no GP in progress, time updated. */
1672
	}
1673
	rsp->fqs_active = 1;
1674
	switch (rsp->fqs_state) {
1675
	case RCU_GP_IDLE:
1676 1677
	case RCU_GP_INIT:

1678
		break; /* grace period idle or initializing, ignore. */
1679 1680 1681 1682 1683

	case RCU_SAVE_DYNTICK:
		if (RCU_SIGNAL_INIT != RCU_SAVE_DYNTICK)
			break; /* So gcc recognizes the dead code. */

L
Lai Jiangshan 已提交
1684 1685
		raw_spin_unlock(&rnp->lock);  /* irqs remain disabled */

1686
		/* Record dyntick-idle state. */
1687
		force_qs_rnp(rsp, dyntick_save_progress_counter);
P
Paul E. McKenney 已提交
1688
		raw_spin_lock(&rnp->lock);  /* irqs already disabled */
1689
		if (rcu_gp_in_progress(rsp))
1690
			rsp->fqs_state = RCU_FORCE_QS;
1691
		break;
1692 1693 1694 1695

	case RCU_FORCE_QS:

		/* Check dyntick-idle state, send IPI to laggarts. */
P
Paul E. McKenney 已提交
1696
		raw_spin_unlock(&rnp->lock);  /* irqs remain disabled */
1697
		force_qs_rnp(rsp, rcu_implicit_dynticks_qs);
1698 1699 1700

		/* Leave state in case more forcing is required. */

P
Paul E. McKenney 已提交
1701
		raw_spin_lock(&rnp->lock);  /* irqs already disabled */
1702
		break;
1703
	}
1704
	rsp->fqs_active = 0;
1705
	if (rsp->fqs_need_gp) {
P
Paul E. McKenney 已提交
1706
		raw_spin_unlock(&rsp->fqslock); /* irqs remain disabled */
1707 1708
		rsp->fqs_need_gp = 0;
		rcu_start_gp(rsp, flags); /* releases rnp->lock */
1709
		trace_rcu_utilization("End fqs");
1710 1711
		return;
	}
P
Paul E. McKenney 已提交
1712
	raw_spin_unlock(&rnp->lock);  /* irqs remain disabled */
1713
unlock_fqs_ret:
P
Paul E. McKenney 已提交
1714
	raw_spin_unlock_irqrestore(&rsp->fqslock, flags);
1715
	trace_rcu_utilization("End fqs");
1716 1717 1718
}

/*
1719 1720 1721
 * 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.
1722 1723 1724 1725 1726 1727
 */
static void
__rcu_process_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
{
	unsigned long flags;

1728 1729
	WARN_ON_ONCE(rdp->beenonline == 0);

1730 1731 1732 1733
	/*
	 * If an RCU GP has gone long enough, go check for dyntick
	 * idle CPUs and, if needed, send resched IPIs.
	 */
1734
	if (ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies))
1735 1736 1737 1738 1739 1740 1741 1742 1743 1744 1745 1746 1747
		force_quiescent_state(rsp, 1);

	/*
	 * Advance callbacks in response to end of earlier grace
	 * period that some other CPU ended.
	 */
	rcu_process_gp_end(rsp, rdp);

	/* 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? */
	if (cpu_needs_another_gp(rsp, rdp)) {
P
Paul E. McKenney 已提交
1748
		raw_spin_lock_irqsave(&rcu_get_root(rsp)->lock, flags);
1749 1750 1751 1752
		rcu_start_gp(rsp, flags);  /* releases above lock */
	}

	/* If there are callbacks ready, invoke them. */
1753
	if (cpu_has_callbacks_ready_to_invoke(rdp))
1754
		invoke_rcu_callbacks(rsp, rdp);
1755 1756
}

1757
/*
1758
 * Do RCU core processing for the current CPU.
1759
 */
1760
static void rcu_process_callbacks(struct softirq_action *unused)
1761
{
1762
	trace_rcu_utilization("Start RCU core");
1763 1764
	__rcu_process_callbacks(&rcu_sched_state,
				&__get_cpu_var(rcu_sched_data));
1765
	__rcu_process_callbacks(&rcu_bh_state, &__get_cpu_var(rcu_bh_data));
1766
	rcu_preempt_process_callbacks();
1767
	trace_rcu_utilization("End RCU core");
1768 1769
}

1770
/*
1771 1772 1773 1774 1775
 * 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.
1776
 */
1777
static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
1778
{
1779 1780
	if (unlikely(!ACCESS_ONCE(rcu_scheduler_fully_active)))
		return;
1781 1782
	if (likely(!rsp->boost)) {
		rcu_do_batch(rsp, rdp);
1783 1784
		return;
	}
1785
	invoke_rcu_callbacks_kthread();
1786 1787
}

1788
static void invoke_rcu_core(void)
1789 1790 1791 1792
{
	raise_softirq(RCU_SOFTIRQ);
}

1793 1794
static void
__call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
1795
	   struct rcu_state *rsp, bool lazy)
1796 1797 1798 1799
{
	unsigned long flags;
	struct rcu_data *rdp;

1800
	WARN_ON_ONCE((unsigned long)head & 0x3); /* Misaligned rcu_head! */
1801
	debug_rcu_head_queue(head);
1802 1803 1804 1805 1806 1807 1808 1809 1810 1811 1812 1813
	head->func = func;
	head->next = NULL;

	smp_mb(); /* Ensure RCU update seen before callback registry. */

	/*
	 * 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);
1814
	WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
1815
	rdp = this_cpu_ptr(rsp->rda);
1816 1817 1818 1819

	/* Add the callback to our list. */
	*rdp->nxttail[RCU_NEXT_TAIL] = head;
	rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
1820
	rdp->qlen++;
1821 1822
	if (lazy)
		rdp->qlen_lazy++;
1823

1824 1825
	if (__is_kfree_rcu_offset((unsigned long)func))
		trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func,
1826
					 rdp->qlen_lazy, rdp->qlen);
1827
	else
1828
		trace_rcu_callback(rsp->name, head, rdp->qlen_lazy, rdp->qlen);
1829

1830 1831 1832 1833 1834
	/* If interrupts were disabled, don't dive into RCU core. */
	if (irqs_disabled_flags(flags)) {
		local_irq_restore(flags);
		return;
	}
1835

1836 1837 1838 1839 1840 1841 1842
	/*
	 * 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.
	 */
1843
	if (unlikely(rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) {
1844 1845 1846 1847 1848 1849 1850 1851 1852 1853 1854 1855 1856 1857 1858 1859 1860 1861 1862 1863 1864

		/* Are we ignoring a completed grace period? */
		rcu_process_gp_end(rsp, rdp);
		check_for_new_grace_period(rsp, rdp);

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

			raw_spin_lock_irqsave(&rnp_root->lock, nestflag);
			rcu_start_gp(rsp, nestflag);  /* rlses rnp_root->lock */
		} 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)
				force_quiescent_state(rsp, 0);
			rdp->n_force_qs_snap = rsp->n_force_qs;
			rdp->qlen_last_fqs_check = rdp->qlen;
		}
1865
	} else if (ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies))
1866 1867 1868 1869 1870
		force_quiescent_state(rsp, 1);
	local_irq_restore(flags);
}

/*
1871
 * Queue an RCU-sched callback for invocation after a grace period.
1872
 */
1873
void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
1874
{
1875
	__call_rcu(head, func, &rcu_sched_state, 0);
1876
}
1877
EXPORT_SYMBOL_GPL(call_rcu_sched);
1878 1879

/*
1880
 * Queue an RCU callback for invocation after a quicker grace period.
1881 1882 1883
 */
void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
{
1884
	__call_rcu(head, func, &rcu_bh_state, 0);
1885 1886 1887
}
EXPORT_SYMBOL_GPL(call_rcu_bh);

1888 1889 1890 1891 1892 1893 1894 1895 1896 1897 1898 1899 1900 1901 1902 1903 1904 1905 1906 1907 1908 1909 1910 1911 1912
/**
 * 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
 * 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.
 *
 * 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)
{
1913 1914 1915 1916
	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");
1917 1918
	if (rcu_blocking_is_gp())
		return;
1919
	wait_rcu_gp(call_rcu_sched);
1920 1921 1922 1923 1924 1925 1926 1927 1928 1929 1930 1931 1932 1933
}
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.
 */
void synchronize_rcu_bh(void)
{
1934 1935 1936 1937
	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");
1938 1939
	if (rcu_blocking_is_gp())
		return;
1940
	wait_rcu_gp(call_rcu_bh);
1941 1942 1943
}
EXPORT_SYMBOL_GPL(synchronize_rcu_bh);

1944 1945 1946 1947 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963
static atomic_t sync_sched_expedited_started = ATOMIC_INIT(0);
static atomic_t sync_sched_expedited_done = ATOMIC_INIT(0);

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;
}

1964 1965 1966 1967 1968 1969 1970 1971 1972 1973
/**
 * 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.
1974
 *
1975 1976 1977 1978
 * Note that it is illegal to call this function while holding any lock
 * that is acquired by a CPU-hotplug notifier.  And yes, it is also illegal
 * to call this function from a CPU-hotplug notifier.  Failing to observe
 * these restriction will result in deadlock.
1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034 2035 2036 2037 2038 2039 2040 2041 2042 2043 2044 2045 2046 2047 2048 2049 2050 2051 2052 2053 2054 2055 2056 2057 2058 2059 2060 2061 2062 2063 2064
 *
 * 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)
{
	int firstsnap, s, snap, trycount = 0;

	/* Note that atomic_inc_return() implies full memory barrier. */
	firstsnap = snap = atomic_inc_return(&sync_sched_expedited_started);
	get_online_cpus();
	WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));

	/*
	 * Each pass through the following loop attempts to force a
	 * context switch on each CPU.
	 */
	while (try_stop_cpus(cpu_online_mask,
			     synchronize_sched_expedited_cpu_stop,
			     NULL) == -EAGAIN) {
		put_online_cpus();

		/* No joy, try again later.  Or just synchronize_sched(). */
		if (trycount++ < 10)
			udelay(trycount * num_online_cpus());
		else {
			synchronize_sched();
			return;
		}

		/* Check to see if someone else did our work for us. */
		s = atomic_read(&sync_sched_expedited_done);
		if (UINT_CMP_GE((unsigned)s, (unsigned)firstsnap)) {
			smp_mb(); /* ensure test happens before caller kfree */
			return;
		}

		/*
		 * Refetching sync_sched_expedited_started allows later
		 * callers to piggyback on our grace period.  We subtract
		 * 1 to get the same token that the last incrementer got.
		 * 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.
		 */
		get_online_cpus();
		snap = atomic_read(&sync_sched_expedited_started);
		smp_mb(); /* ensure read is before try_stop_cpus(). */
	}

	/*
	 * 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
	 * than we did beat us to the punch.
	 */
	do {
		s = atomic_read(&sync_sched_expedited_done);
		if (UINT_CMP_GE((unsigned)s, (unsigned)snap)) {
			smp_mb(); /* ensure test happens before caller kfree */
			break;
		}
	} while (atomic_cmpxchg(&sync_sched_expedited_done, s, snap) != s);

	put_online_cpus();
}
EXPORT_SYMBOL_GPL(synchronize_sched_expedited);

2065 2066 2067 2068 2069 2070 2071 2072 2073
/*
 * 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)
{
2074 2075
	struct rcu_node *rnp = rdp->mynode;

2076 2077 2078 2079 2080 2081
	rdp->n_rcu_pending++;

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

	/* Is the RCU core waiting for a quiescent state from this CPU? */
2082 2083
	if (rcu_scheduler_fully_active &&
	    rdp->qs_pending && !rdp->passed_quiesce) {
2084 2085 2086 2087 2088 2089

		/*
		 * If force_quiescent_state() coming soon and this CPU
		 * needs a quiescent state, and this is either RCU-sched
		 * or RCU-bh, force a local reschedule.
		 */
2090
		rdp->n_rp_qs_pending++;
P
Paul E. McKenney 已提交
2091
		if (!rdp->preemptible &&
2092 2093 2094
		    ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs) - 1,
				 jiffies))
			set_need_resched();
2095
	} else if (rdp->qs_pending && rdp->passed_quiesce) {
2096
		rdp->n_rp_report_qs++;
2097
		return 1;
2098
	}
2099 2100

	/* Does this CPU have callbacks ready to invoke? */
2101 2102
	if (cpu_has_callbacks_ready_to_invoke(rdp)) {
		rdp->n_rp_cb_ready++;
2103
		return 1;
2104
	}
2105 2106

	/* Has RCU gone idle with this CPU needing another grace period? */
2107 2108
	if (cpu_needs_another_gp(rsp, rdp)) {
		rdp->n_rp_cpu_needs_gp++;
2109
		return 1;
2110
	}
2111 2112

	/* Has another RCU grace period completed?  */
2113
	if (ACCESS_ONCE(rnp->completed) != rdp->completed) { /* outside lock */
2114
		rdp->n_rp_gp_completed++;
2115
		return 1;
2116
	}
2117 2118

	/* Has a new RCU grace period started? */
2119
	if (ACCESS_ONCE(rnp->gpnum) != rdp->gpnum) { /* outside lock */
2120
		rdp->n_rp_gp_started++;
2121
		return 1;
2122
	}
2123 2124

	/* Has an RCU GP gone long enough to send resched IPIs &c? */
2125
	if (rcu_gp_in_progress(rsp) &&
2126
	    ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies)) {
2127
		rdp->n_rp_need_fqs++;
2128
		return 1;
2129
	}
2130 2131

	/* nothing to do */
2132
	rdp->n_rp_need_nothing++;
2133 2134 2135 2136 2137 2138 2139 2140
	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.
 */
2141
static int rcu_pending(int cpu)
2142
{
2143
	return __rcu_pending(&rcu_sched_state, &per_cpu(rcu_sched_data, cpu)) ||
2144 2145
	       __rcu_pending(&rcu_bh_state, &per_cpu(rcu_bh_data, cpu)) ||
	       rcu_preempt_pending(cpu);
2146 2147 2148 2149 2150
}

/*
 * Check to see if any future RCU-related work will need to be done
 * by the current CPU, even if none need be done immediately, returning
2151
 * 1 if so.
2152
 */
2153
static int rcu_cpu_has_callbacks(int cpu)
2154 2155
{
	/* RCU callbacks either ready or pending? */
2156
	return per_cpu(rcu_sched_data, cpu).nxtlist ||
2157
	       per_cpu(rcu_bh_data, cpu).nxtlist ||
2158
	       rcu_preempt_cpu_has_callbacks(cpu);
2159 2160
}

2161 2162 2163 2164 2165 2166 2167 2168 2169 2170 2171 2172 2173 2174 2175 2176 2177 2178 2179 2180 2181 2182 2183 2184 2185 2186 2187 2188 2189 2190
static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL};
static atomic_t rcu_barrier_cpu_count;
static DEFINE_MUTEX(rcu_barrier_mutex);
static struct completion rcu_barrier_completion;

static void rcu_barrier_callback(struct rcu_head *notused)
{
	if (atomic_dec_and_test(&rcu_barrier_cpu_count))
		complete(&rcu_barrier_completion);
}

/*
 * Called with preemption disabled, and from cross-cpu IRQ context.
 */
static void rcu_barrier_func(void *type)
{
	int cpu = smp_processor_id();
	struct rcu_head *head = &per_cpu(rcu_barrier_head, cpu);
	void (*call_rcu_func)(struct rcu_head *head,
			      void (*func)(struct rcu_head *head));

	atomic_inc(&rcu_barrier_cpu_count);
	call_rcu_func = type;
	call_rcu_func(head, rcu_barrier_callback);
}

/*
 * Orchestrate the specified type of RCU barrier, waiting for all
 * RCU callbacks of the specified type to complete.
 */
2191 2192
static void _rcu_barrier(struct rcu_state *rsp,
			 void (*call_rcu_func)(struct rcu_head *head,
2193 2194 2195
					       void (*func)(struct rcu_head *head)))
{
	BUG_ON(in_interrupt());
2196
	/* Take mutex to serialize concurrent rcu_barrier() requests. */
2197 2198 2199 2200 2201 2202 2203 2204 2205
	mutex_lock(&rcu_barrier_mutex);
	init_completion(&rcu_barrier_completion);
	/*
	 * Initialize rcu_barrier_cpu_count to 1, then invoke
	 * rcu_barrier_func() on each CPU, so that each CPU also has
	 * incremented rcu_barrier_cpu_count.  Only then is it safe to
	 * decrement rcu_barrier_cpu_count -- otherwise the first CPU
	 * might complete its grace period before all of the other CPUs
	 * did their increment, causing this function to return too
2206 2207 2208
	 * early.  Note that on_each_cpu() disables irqs, which prevents
	 * any CPUs from coming online or going offline until each online
	 * CPU has queued its RCU-barrier callback.
2209 2210 2211 2212 2213 2214 2215 2216 2217 2218 2219 2220 2221 2222
	 */
	atomic_set(&rcu_barrier_cpu_count, 1);
	on_each_cpu(rcu_barrier_func, (void *)call_rcu_func, 1);
	if (atomic_dec_and_test(&rcu_barrier_cpu_count))
		complete(&rcu_barrier_completion);
	wait_for_completion(&rcu_barrier_completion);
	mutex_unlock(&rcu_barrier_mutex);
}

/**
 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
 */
void rcu_barrier_bh(void)
{
2223
	_rcu_barrier(&rcu_bh_state, call_rcu_bh);
2224 2225 2226 2227 2228 2229 2230 2231
}
EXPORT_SYMBOL_GPL(rcu_barrier_bh);

/**
 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
 */
void rcu_barrier_sched(void)
{
2232
	_rcu_barrier(&rcu_sched_state, call_rcu_sched);
2233 2234 2235
}
EXPORT_SYMBOL_GPL(rcu_barrier_sched);

2236
/*
2237
 * Do boot-time initialization of a CPU's per-CPU RCU data.
2238
 */
2239 2240
static void __init
rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
2241 2242 2243
{
	unsigned long flags;
	int i;
2244
	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
2245 2246 2247
	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
2248
	raw_spin_lock_irqsave(&rnp->lock, flags);
2249 2250 2251 2252
	rdp->grpmask = 1UL << (cpu - rdp->mynode->grplo);
	rdp->nxtlist = NULL;
	for (i = 0; i < RCU_NEXT_SIZE; i++)
		rdp->nxttail[i] = &rdp->nxtlist;
2253
	rdp->qlen_lazy = 0;
2254 2255
	rdp->qlen = 0;
	rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
2256
	WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_NESTING);
2257
	WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1);
2258
	rdp->cpu = cpu;
2259
	rdp->rsp = rsp;
P
Paul E. McKenney 已提交
2260
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
2261 2262 2263 2264 2265 2266 2267
}

/*
 * 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.
2268
 */
2269
static void __cpuinit
P
Paul E. McKenney 已提交
2270
rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptible)
2271 2272 2273
{
	unsigned long flags;
	unsigned long mask;
2274
	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
2275 2276 2277
	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
2278
	raw_spin_lock_irqsave(&rnp->lock, flags);
2279
	rdp->beenonline = 1;	 /* We have now been online. */
P
Paul E. McKenney 已提交
2280
	rdp->preemptible = preemptible;
2281 2282
	rdp->qlen_last_fqs_check = 0;
	rdp->n_force_qs_snap = rsp->n_force_qs;
2283
	rdp->blimit = blimit;
2284 2285 2286
	rdp->dynticks->dynticks_nesting = DYNTICK_TASK_NESTING;
	atomic_set(&rdp->dynticks->dynticks,
		   (atomic_read(&rdp->dynticks->dynticks) & ~0x1) + 1);
2287
	rcu_prepare_for_idle_init(cpu);
P
Paul E. McKenney 已提交
2288
	raw_spin_unlock(&rnp->lock);		/* irqs remain disabled. */
2289 2290 2291 2292 2293 2294 2295

	/*
	 * A new grace period might start here.  If so, we won't be part
	 * of it, but that is OK, as we are currently in a quiescent state.
	 */

	/* Exclude any attempts to start a new GP on large systems. */
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Paul E. McKenney 已提交
2296
	raw_spin_lock(&rsp->onofflock);		/* irqs already disabled. */
2297 2298 2299 2300 2301 2302

	/* 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
2303
		raw_spin_lock(&rnp->lock);	/* irqs already disabled. */
2304 2305
		rnp->qsmaskinit |= mask;
		mask = rnp->grpmask;
2306
		if (rnp == rdp->mynode) {
2307 2308 2309 2310 2311 2312
			/*
			 * 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;
2313
			rdp->completed = rnp->completed;
2314 2315
			rdp->passed_quiesce = 0;
			rdp->qs_pending = 0;
2316
			rdp->passed_quiesce_gpnum = rnp->gpnum - 1;
2317
			trace_rcu_grace_period(rsp->name, rdp->gpnum, "cpuonl");
2318
		}
P
Paul E. McKenney 已提交
2319
		raw_spin_unlock(&rnp->lock); /* irqs already disabled. */
2320 2321 2322
		rnp = rnp->parent;
	} while (rnp != NULL && !(rnp->qsmaskinit & mask));

P
Paul E. McKenney 已提交
2323
	raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
2324 2325
}

P
Peter Zijlstra 已提交
2326
static void __cpuinit rcu_prepare_cpu(int cpu)
2327
{
2328 2329 2330
	rcu_init_percpu_data(cpu, &rcu_sched_state, 0);
	rcu_init_percpu_data(cpu, &rcu_bh_state, 0);
	rcu_preempt_init_percpu_data(cpu);
2331 2332 2333
}

/*
2334
 * Handle CPU online/offline notification events.
2335
 */
2336 2337
static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
				    unsigned long action, void *hcpu)
2338 2339
{
	long cpu = (long)hcpu;
2340
	struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
2341
	struct rcu_node *rnp = rdp->mynode;
2342

2343
	trace_rcu_utilization("Start CPU hotplug");
2344 2345 2346
	switch (action) {
	case CPU_UP_PREPARE:
	case CPU_UP_PREPARE_FROZEN:
P
Peter Zijlstra 已提交
2347 2348
		rcu_prepare_cpu(cpu);
		rcu_prepare_kthreads(cpu);
2349 2350
		break;
	case CPU_ONLINE:
2351 2352
	case CPU_DOWN_FAILED:
		rcu_node_kthread_setaffinity(rnp, -1);
2353
		rcu_cpu_kthread_setrt(cpu, 1);
2354 2355 2356
		break;
	case CPU_DOWN_PREPARE:
		rcu_node_kthread_setaffinity(rnp, cpu);
2357
		rcu_cpu_kthread_setrt(cpu, 0);
2358
		break;
2359 2360 2361
	case CPU_DYING:
	case CPU_DYING_FROZEN:
		/*
2362 2363 2364
		 * The whole machine is "stopped" except this CPU, so we can
		 * touch any data without introducing corruption. We send the
		 * dying CPU's callbacks to an arbitrarily chosen online CPU.
2365
		 */
2366 2367 2368
		rcu_cleanup_dying_cpu(&rcu_bh_state);
		rcu_cleanup_dying_cpu(&rcu_sched_state);
		rcu_preempt_cleanup_dying_cpu();
2369
		rcu_cleanup_after_idle(cpu);
2370
		break;
2371 2372 2373 2374
	case CPU_DEAD:
	case CPU_DEAD_FROZEN:
	case CPU_UP_CANCELED:
	case CPU_UP_CANCELED_FROZEN:
2375 2376 2377
		rcu_cleanup_dead_cpu(cpu, &rcu_bh_state);
		rcu_cleanup_dead_cpu(cpu, &rcu_sched_state);
		rcu_preempt_cleanup_dead_cpu(cpu);
2378 2379 2380 2381
		break;
	default:
		break;
	}
2382
	trace_rcu_utilization("End CPU hotplug");
2383 2384 2385
	return NOTIFY_OK;
}

2386 2387 2388 2389 2390 2391 2392 2393 2394 2395 2396 2397 2398 2399 2400
/*
 * 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;
}

2401 2402 2403 2404 2405 2406 2407 2408 2409
/*
 * 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;

2410
	for (i = NUM_RCU_LVLS - 1; i > 0; i--)
2411
		rsp->levelspread[i] = CONFIG_RCU_FANOUT;
2412
	rsp->levelspread[0] = RCU_FANOUT_LEAF;
2413 2414 2415 2416 2417 2418 2419 2420 2421 2422 2423 2424 2425 2426 2427 2428 2429 2430 2431 2432
}
#else /* #ifdef CONFIG_RCU_FANOUT_EXACT */
static void __init rcu_init_levelspread(struct rcu_state *rsp)
{
	int ccur;
	int cprv;
	int i;

	cprv = NR_CPUS;
	for (i = NUM_RCU_LVLS - 1; i >= 0; i--) {
		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.
 */
2433 2434
static void __init rcu_init_one(struct rcu_state *rsp,
		struct rcu_data __percpu *rda)
2435
{
2436 2437 2438 2439
	static char *buf[] = { "rcu_node_level_0",
			       "rcu_node_level_1",
			       "rcu_node_level_2",
			       "rcu_node_level_3" };  /* Match MAX_RCU_LVLS */
2440 2441 2442 2443 2444
	int cpustride = 1;
	int i;
	int j;
	struct rcu_node *rnp;

2445 2446
	BUILD_BUG_ON(MAX_RCU_LVLS > ARRAY_SIZE(buf));  /* Fix buf[] init! */

2447 2448 2449 2450 2451 2452 2453 2454 2455 2456 2457 2458
	/* Initialize the level-tracking arrays. */

	for (i = 1; i < NUM_RCU_LVLS; i++)
		rsp->level[i] = rsp->level[i - 1] + rsp->levelcnt[i - 1];
	rcu_init_levelspread(rsp);

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

	for (i = NUM_RCU_LVLS - 1; i >= 0; i--) {
		cpustride *= rsp->levelspread[i];
		rnp = rsp->level[i];
		for (j = 0; j < rsp->levelcnt[i]; j++, rnp++) {
P
Paul E. McKenney 已提交
2459
			raw_spin_lock_init(&rnp->lock);
2460 2461
			lockdep_set_class_and_name(&rnp->lock,
						   &rcu_node_class[i], buf[i]);
2462
			rnp->gpnum = 0;
2463 2464 2465 2466 2467 2468 2469 2470 2471 2472 2473 2474 2475 2476 2477 2478 2479
			rnp->qsmask = 0;
			rnp->qsmaskinit = 0;
			rnp->grplo = j * cpustride;
			rnp->grphi = (j + 1) * cpustride - 1;
			if (rnp->grphi >= NR_CPUS)
				rnp->grphi = NR_CPUS - 1;
			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;
2480
			INIT_LIST_HEAD(&rnp->blkd_tasks);
2481 2482
		}
	}
2483

2484
	rsp->rda = rda;
2485 2486
	rnp = rsp->level[NUM_RCU_LVLS - 1];
	for_each_possible_cpu(i) {
2487
		while (i > rnp->grphi)
2488
			rnp++;
2489
		per_cpu_ptr(rsp->rda, i)->mynode = rnp;
2490 2491
		rcu_boot_init_percpu_data(i, rsp);
	}
2492 2493
}

2494
void __init rcu_init(void)
2495
{
P
Paul E. McKenney 已提交
2496
	int cpu;
2497

2498
	rcu_bootup_announce();
2499 2500
	rcu_init_one(&rcu_sched_state, &rcu_sched_data);
	rcu_init_one(&rcu_bh_state, &rcu_bh_data);
2501
	__rcu_init_preempt();
2502
	 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
2503 2504 2505 2506 2507 2508 2509

	/*
	 * 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);
P
Paul E. McKenney 已提交
2510 2511
	for_each_online_cpu(cpu)
		rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
2512
	check_cpu_stall_init();
2513 2514
}

2515
#include "rcutree_plugin.h"