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/*
 * Read-Copy Update mechanism for mutual exclusion
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
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 * along with this program; if not, you can access it online at
 * http://www.gnu.org/licenses/gpl-2.0.html.
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 *
 * Copyright IBM Corporation, 2008
 *
 * Authors: Dipankar Sarma <dipankar@in.ibm.com>
 *	    Manfred Spraul <manfred@colorfullife.com>
 *	    Paul E. McKenney <paulmck@linux.vnet.ibm.com> Hierarchical version
 *
 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
 *
 * For detailed explanation of Read-Copy Update mechanism see -
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 *	Documentation/RCU
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 */
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/spinlock.h>
#include <linux/smp.h>
#include <linux/rcupdate.h>
#include <linux/interrupt.h>
#include <linux/sched.h>
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#include <linux/nmi.h>
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#include <linux/atomic.h>
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#include <linux/bitops.h>
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#include <linux/export.h>
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#include <linux/completion.h>
#include <linux/moduleparam.h>
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#include <linux/module.h>
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#include <linux/percpu.h>
#include <linux/notifier.h>
#include <linux/cpu.h>
#include <linux/mutex.h>
#include <linux/time.h>
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#include <linux/kernel_stat.h>
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#include <linux/wait.h>
#include <linux/kthread.h>
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#include <linux/prefetch.h>
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#include <linux/delay.h>
#include <linux/stop_machine.h>
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#include <linux/random.h>
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#include <linux/ftrace_event.h>
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#include <linux/suspend.h>
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#include "tree.h"
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#include "rcu.h"
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MODULE_ALIAS("rcutree");
#ifdef MODULE_PARAM_PREFIX
#undef MODULE_PARAM_PREFIX
#endif
#define MODULE_PARAM_PREFIX "rcutree."

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/* Data structures. */

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static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
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static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
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/*
 * In order to export the rcu_state name to the tracing tools, it
 * needs to be added in the __tracepoint_string section.
 * This requires defining a separate variable tp_<sname>_varname
 * that points to the string being used, and this will allow
 * the tracing userspace tools to be able to decipher the string
 * address to the matching string.
 */
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#define RCU_STATE_INITIALIZER(sname, sabbr, cr) \
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static char sname##_varname[] = #sname; \
static const char *tp_##sname##_varname __used __tracepoint_string = sname##_varname; \
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struct rcu_state sname##_state = { \
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	.level = { &sname##_state.node[0] }, \
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	.call = cr, \
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	.fqs_state = RCU_GP_IDLE, \
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	.gpnum = 0UL - 300UL, \
	.completed = 0UL - 300UL, \
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	.orphan_lock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.orphan_lock), \
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	.orphan_nxttail = &sname##_state.orphan_nxtlist, \
	.orphan_donetail = &sname##_state.orphan_donelist, \
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	.barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \
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	.onoff_mutex = __MUTEX_INITIALIZER(sname##_state.onoff_mutex), \
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	.name = sname##_varname, \
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	.abbr = sabbr, \
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}; \
DEFINE_PER_CPU(struct rcu_data, sname##_data)
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RCU_STATE_INITIALIZER(rcu_sched, 's', call_rcu_sched);
RCU_STATE_INITIALIZER(rcu_bh, 'b', call_rcu_bh);
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static struct rcu_state *rcu_state;
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LIST_HEAD(rcu_struct_flavors);
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/* Increase (but not decrease) the CONFIG_RCU_FANOUT_LEAF at boot time. */
static int rcu_fanout_leaf = CONFIG_RCU_FANOUT_LEAF;
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module_param(rcu_fanout_leaf, int, 0444);
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int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;
static int num_rcu_lvl[] = {  /* Number of rcu_nodes at specified level. */
	NUM_RCU_LVL_0,
	NUM_RCU_LVL_1,
	NUM_RCU_LVL_2,
	NUM_RCU_LVL_3,
	NUM_RCU_LVL_4,
};
int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */

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

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

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#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(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_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu);
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static void invoke_rcu_core(void);
static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp);
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/*
 * Track the rcutorture test sequence number and the update version
 * number within a given test.  The rcutorture_testseq is incremented
 * on every rcutorture module load and unload, so has an odd value
 * when a test is running.  The rcutorture_vernum is set to zero
 * when rcutorture starts and is incremented on each rcutorture update.
 * These variables enable correlating rcutorture output with the
 * RCU tracing information.
 */
unsigned long rcutorture_testseq;
unsigned long rcutorture_vernum;

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

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/*
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 * Note a quiescent state.  Because we do not need to know
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 * how many quiescent states passed, just if there was at least
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 * one since the start of the grace period, this just sets a flag.
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 * The caller must have disabled preemption.
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 */
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void rcu_sched_qs(int cpu)
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{
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	struct rcu_data *rdp = &per_cpu(rcu_sched_data, cpu);
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	if (rdp->passed_quiesce == 0)
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		trace_rcu_grace_period(TPS("rcu_sched"), rdp->gpnum, TPS("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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	if (rdp->passed_quiesce == 0)
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		trace_rcu_grace_period(TPS("rcu_bh"), rdp->gpnum, TPS("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(TPS("Start context switch"));
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	rcu_sched_qs(cpu);
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	rcu_preempt_note_context_switch(cpu);
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	trace_rcu_utilization(TPS("End context switch"));
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}
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EXPORT_SYMBOL_GPL(rcu_note_context_switch);
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static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
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	.dynticks_nesting = DYNTICK_TASK_EXIT_IDLE,
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	.dynticks = ATOMIC_INIT(1),
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#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
	.dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE,
	.dynticks_idle = ATOMIC_INIT(1),
#endif /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
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};
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static long blimit = 10;	/* Maximum callbacks per rcu_do_batch. */
static long qhimark = 10000;	/* If this many pending, ignore blimit. */
static long qlowmark = 100;	/* Once only this many pending, use blimit. */
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module_param(blimit, long, 0444);
module_param(qhimark, long, 0444);
module_param(qlowmark, long, 0444);
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static ulong jiffies_till_first_fqs = ULONG_MAX;
static ulong jiffies_till_next_fqs = ULONG_MAX;
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module_param(jiffies_till_first_fqs, ulong, 0644);
module_param(jiffies_till_next_fqs, ulong, 0644);

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static void rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
				  struct rcu_data *rdp);
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static void force_qs_rnp(struct rcu_state *rsp,
			 int (*f)(struct rcu_data *rsp, bool *isidle,
				  unsigned long *maxj),
			 bool *isidle, unsigned long *maxj);
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static void force_quiescent_state(struct rcu_state *rsp);
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static int rcu_pending(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)
{
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	force_quiescent_state(&rcu_bh_state);
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}
EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state);

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/*
 * 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)
{
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	force_quiescent_state(&rcu_sched_state);
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}
EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state);

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

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

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

	return ACCESS_ONCE(*fp);
}

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

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/*
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 * rcu_eqs_enter_common - current CPU is moving towards extended quiescent state
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 *
 * If the new value of the ->dynticks_nesting counter now is zero,
 * we really have entered idle, and must do the appropriate accounting.
 * The caller must have disabled interrupts.
 */
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static void rcu_eqs_enter_common(struct rcu_dynticks *rdtp, long long oldval,
				bool user)
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{
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	struct rcu_state *rsp;
	struct rcu_data *rdp;

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	trace_rcu_dyntick(TPS("Start"), oldval, rdtp->dynticks_nesting);
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	if (!user && !is_idle_task(current)) {
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		struct task_struct *idle __maybe_unused =
			idle_task(smp_processor_id());
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		trace_rcu_dyntick(TPS("Error on entry: not idle task"), oldval, 0);
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		ftrace_dump(DUMP_ORIG);
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		WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
			  current->pid, current->comm,
			  idle->pid, idle->comm); /* must be idle task! */
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	}
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	for_each_rcu_flavor(rsp) {
		rdp = this_cpu_ptr(rsp->rda);
		do_nocb_deferred_wakeup(rdp);
	}
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	rcu_prepare_for_idle(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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	/*
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	 * It is illegal to enter an extended quiescent state while
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	 * in an RCU read-side critical section.
	 */
	rcu_lockdep_assert(!lock_is_held(&rcu_lock_map),
			   "Illegal idle entry in RCU read-side critical section.");
	rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map),
			   "Illegal idle entry in RCU-bh read-side critical section.");
	rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map),
			   "Illegal idle entry in RCU-sched read-side critical section.");
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}
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/*
 * Enter an RCU extended quiescent state, which can be either the
 * idle loop or adaptive-tickless usermode execution.
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 */
425
static void rcu_eqs_enter(bool user)
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{
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	long long oldval;
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	struct rcu_dynticks *rdtp;

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	rdtp = this_cpu_ptr(&rcu_dynticks);
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	oldval = rdtp->dynticks_nesting;
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	WARN_ON_ONCE((oldval & DYNTICK_TASK_NEST_MASK) == 0);
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	if ((oldval & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE) {
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		rdtp->dynticks_nesting = 0;
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		rcu_eqs_enter_common(rdtp, oldval, user);
	} else {
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		rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE;
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	}
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}
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/**
 * rcu_idle_enter - inform RCU that current CPU is entering idle
 *
 * Enter idle mode, in other words, -leave- the mode in which RCU
 * read-side critical sections can occur.  (Though RCU read-side
 * critical sections can occur in irq handlers in idle, a possibility
 * handled by irq_enter() and irq_exit().)
 *
 * We crowbar the ->dynticks_nesting field to zero to allow for
 * the possibility of usermode upcalls having messed up our count
 * of interrupt nesting level during the prior busy period.
 */
void rcu_idle_enter(void)
{
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	unsigned long flags;

	local_irq_save(flags);
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	rcu_eqs_enter(false);
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	rcu_sysidle_enter(this_cpu_ptr(&rcu_dynticks), 0);
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	local_irq_restore(flags);
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}
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EXPORT_SYMBOL_GPL(rcu_idle_enter);
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#ifdef CONFIG_RCU_USER_QS
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/**
 * rcu_user_enter - inform RCU that we are resuming userspace.
 *
 * Enter RCU idle mode right before resuming userspace.  No use of RCU
 * is permitted between this call and rcu_user_exit(). This way the
 * CPU doesn't need to maintain the tick for RCU maintenance purposes
 * when the CPU runs in userspace.
 */
void rcu_user_enter(void)
{
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	rcu_eqs_enter(1);
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}
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#endif /* CONFIG_RCU_USER_QS */
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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);
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	rdtp = this_cpu_ptr(&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)
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		trace_rcu_dyntick(TPS("--="), oldval, rdtp->dynticks_nesting);
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	else
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		rcu_eqs_enter_common(rdtp, oldval, true);
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	rcu_sysidle_enter(rdtp, 1);
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	local_irq_restore(flags);
}

/*
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 * rcu_eqs_exit_common - current CPU moving away from extended quiescent state
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 *
 * 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.
 */
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static void rcu_eqs_exit_common(struct rcu_dynticks *rdtp, long long oldval,
			       int user)
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{
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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(TPS("End"), oldval, rdtp->dynticks_nesting);
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	if (!user && !is_idle_task(current)) {
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		struct task_struct *idle __maybe_unused =
			idle_task(smp_processor_id());
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		trace_rcu_dyntick(TPS("Error on exit: not idle task"),
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				  oldval, rdtp->dynticks_nesting);
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		ftrace_dump(DUMP_ORIG);
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		WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
			  current->pid, current->comm,
			  idle->pid, idle->comm); /* must be idle task! */
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	}
}

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

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	rdtp = this_cpu_ptr(&rcu_dynticks);
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	oldval = rdtp->dynticks_nesting;
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	WARN_ON_ONCE(oldval < 0);
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	if (oldval & DYNTICK_TASK_NEST_MASK) {
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		rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
558
	} else {
559
		rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
560 561
		rcu_eqs_exit_common(rdtp, oldval, user);
	}
562
}
563 564 565 566 567 568 569 570 571 572 573 574 575 576

/**
 * rcu_idle_exit - inform RCU that current CPU is leaving idle
 *
 * Exit idle mode, in other words, -enter- the mode in which RCU
 * read-side critical sections can occur.
 *
 * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST to
 * allow for the possibility of usermode upcalls messing up our count
 * of interrupt nesting level during the busy period that is just
 * now starting.
 */
void rcu_idle_exit(void)
{
577 578 579
	unsigned long flags;

	local_irq_save(flags);
580
	rcu_eqs_exit(false);
581
	rcu_sysidle_exit(this_cpu_ptr(&rcu_dynticks), 0);
582
	local_irq_restore(flags);
583
}
584
EXPORT_SYMBOL_GPL(rcu_idle_exit);
585

586
#ifdef CONFIG_RCU_USER_QS
587 588 589 590 591 592 593 594
/**
 * rcu_user_exit - inform RCU that we are exiting userspace.
 *
 * Exit RCU idle mode while entering the kernel because it can
 * run a RCU read side critical section anytime.
 */
void rcu_user_exit(void)
{
595
	rcu_eqs_exit(1);
596
}
597
#endif /* CONFIG_RCU_USER_QS */
598

599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624
/**
 * 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);
625
	rdtp = this_cpu_ptr(&rcu_dynticks);
626 627 628
	oldval = rdtp->dynticks_nesting;
	rdtp->dynticks_nesting++;
	WARN_ON_ONCE(rdtp->dynticks_nesting == 0);
629
	if (oldval)
630
		trace_rcu_dyntick(TPS("++="), oldval, rdtp->dynticks_nesting);
631
	else
632
		rcu_eqs_exit_common(rdtp, oldval, true);
633
	rcu_sysidle_exit(rdtp, 1);
634 635 636 637 638 639 640 641 642 643 644 645
	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)
{
646
	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
647

648 649
	if (rdtp->dynticks_nmi_nesting == 0 &&
	    (atomic_read(&rdtp->dynticks) & 0x1))
650
		return;
651 652 653 654 655 656
	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));
657 658 659 660 661 662 663 664 665 666 667
}

/**
 * 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)
{
668
	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
669

670 671
	if (rdtp->dynticks_nmi_nesting == 0 ||
	    --rdtp->dynticks_nmi_nesting != 0)
672
		return;
673 674 675 676 677
	/* 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);
678 679 680
}

/**
681 682 683 684 685 686 687
 * __rcu_is_watching - are RCU read-side critical sections safe?
 *
 * Return true if RCU is watching the running CPU, which means that
 * this CPU can safely enter RCU read-side critical sections.  Unlike
 * rcu_is_watching(), the caller of __rcu_is_watching() must have at
 * least disabled preemption.
 */
688
bool notrace __rcu_is_watching(void)
689 690 691 692 693 694
{
	return atomic_read(this_cpu_ptr(&rcu_dynticks.dynticks)) & 0x1;
}

/**
 * rcu_is_watching - see if RCU thinks that the current CPU is idle
695
 *
696
 * If the current CPU is in its idle loop and is neither in an interrupt
697
 * or NMI handler, return true.
698
 */
699
bool notrace rcu_is_watching(void)
700
{
701 702 703
	int ret;

	preempt_disable();
704
	ret = __rcu_is_watching();
705 706
	preempt_enable();
	return ret;
707
}
708
EXPORT_SYMBOL_GPL(rcu_is_watching);
709

710
#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
711 712 713 714 715 716 717

/*
 * 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
718 719 720 721 722 723 724 725 726 727 728
 * 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.
729 730 731 732 733 734
 *
 * Disable checking if in an NMI handler because we cannot safely report
 * errors from NMI handlers anyway.
 */
bool rcu_lockdep_current_cpu_online(void)
{
735 736
	struct rcu_data *rdp;
	struct rcu_node *rnp;
737 738 739
	bool ret;

	if (in_nmi())
F
Fengguang Wu 已提交
740
		return true;
741
	preempt_disable();
742
	rdp = this_cpu_ptr(&rcu_sched_data);
743 744
	rnp = rdp->mynode;
	ret = (rdp->grpmask & rnp->qsmaskinit) ||
745 746 747 748 749 750
	      !rcu_scheduler_fully_active;
	preempt_enable();
	return ret;
}
EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);

751
#endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
752

753
/**
754
 * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle
755
 *
756 757 758
 * 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.
759
 */
760
static int rcu_is_cpu_rrupt_from_idle(void)
761
{
762
	return __this_cpu_read(rcu_dynticks.dynticks_nesting) <= 1;
763 764 765 766 767
}

/*
 * Snapshot the specified CPU's dynticks counter so that we can later
 * credit them with an implicit quiescent state.  Return 1 if this CPU
768
 * is in dynticks idle mode, which is an extended quiescent state.
769
 */
770 771
static int dyntick_save_progress_counter(struct rcu_data *rdp,
					 bool *isidle, unsigned long *maxj)
772
{
773
	rdp->dynticks_snap = atomic_add_return(0, &rdp->dynticks->dynticks);
774
	rcu_sysidle_check_cpu(rdp, isidle, maxj);
775
	return (rdp->dynticks_snap & 0x1) == 0;
776 777
}

778 779 780 781 782 783
/*
 * This function really isn't for public consumption, but RCU is special in
 * that context switches can allow the state machine to make progress.
 */
extern void resched_cpu(int cpu);

784 785 786 787
/*
 * 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()
788
 * for this same CPU, or by virtue of having been offline.
789
 */
790 791
static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
				    bool *isidle, unsigned long *maxj)
792
{
793 794
	unsigned int curr;
	unsigned int snap;
795

796 797
	curr = (unsigned int)atomic_add_return(0, &rdp->dynticks->dynticks);
	snap = (unsigned int)rdp->dynticks_snap;
798 799 800 801 802 803 804 805 806

	/*
	 * 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.
	 */
807
	if ((curr & 0x1) == 0 || UINT_CMP_GE(curr, snap + 2)) {
808
		trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
809 810 811 812
		rdp->dynticks_fqs++;
		return 1;
	}

813 814 815 816 817 818 819 820 821 822 823 824 825 826 827
	/*
	 * Check for the CPU being offline, but only if the grace period
	 * is old enough.  We don't need to worry about the CPU changing
	 * state: If we see it offline even once, it has been through a
	 * quiescent state.
	 *
	 * The reason for insisting that the grace period be at least
	 * one jiffy old is that CPUs that are not quite online and that
	 * have just gone offline can still execute RCU read-side critical
	 * sections.
	 */
	if (ULONG_CMP_GE(rdp->rsp->gp_start + 2, jiffies))
		return 0;  /* Grace period is not old enough. */
	barrier();
	if (cpu_is_offline(rdp->cpu)) {
828
		trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("ofl"));
829 830 831
		rdp->offline_fqs++;
		return 1;
	}
832 833 834 835 836 837 838 839 840 841

	/*
	 * There is a possibility that a CPU in adaptive-ticks state
	 * might run in the kernel with the scheduling-clock tick disabled
	 * for an extended time period.  Invoke rcu_kick_nohz_cpu() to
	 * force the CPU to restart the scheduling-clock tick in this
	 * CPU is in this state.
	 */
	rcu_kick_nohz_cpu(rdp->cpu);

842 843 844 845 846 847 848 849 850 851
	/*
	 * Alternatively, the CPU might be running in the kernel
	 * for an extended period of time without a quiescent state.
	 * Attempt to force the CPU through the scheduler to gain the
	 * needed quiescent state, but only if the grace period has gone
	 * on for an uncommonly long time.  If there are many stuck CPUs,
	 * we will beat on the first one until it gets unstuck, then move
	 * to the next.  Only do this for the primary flavor of RCU.
	 */
	if (rdp->rsp == rcu_state &&
852
	    ULONG_CMP_GE(jiffies, rdp->rsp->jiffies_resched)) {
853 854 855 856
		rdp->rsp->jiffies_resched += 5;
		resched_cpu(rdp->cpu);
	}

857
	return 0;
858 859 860 861
}

static void record_gp_stall_check_time(struct rcu_state *rsp)
{
862
	unsigned long j = jiffies;
863
	unsigned long j1;
864 865 866

	rsp->gp_start = j;
	smp_wmb(); /* Record start time before stall time. */
867
	j1 = rcu_jiffies_till_stall_check();
868
	ACCESS_ONCE(rsp->jiffies_stall) = j + j1;
869
	rsp->jiffies_resched = j + j1 / 2;
870 871
}

872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894
/*
 * Dump stacks of all tasks running on stalled CPUs.  This is a fallback
 * for architectures that do not implement trigger_all_cpu_backtrace().
 * The NMI-triggered stack traces are more accurate because they are
 * printed by the target CPU.
 */
static void rcu_dump_cpu_stacks(struct rcu_state *rsp)
{
	int cpu;
	unsigned long flags;
	struct rcu_node *rnp;

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

895 896 897 898 899
static void print_other_cpu_stall(struct rcu_state *rsp)
{
	int cpu;
	long delta;
	unsigned long flags;
900
	int ndetected = 0;
901
	struct rcu_node *rnp = rcu_get_root(rsp);
902
	long totqlen = 0;
903 904 905

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

P
Paul E. McKenney 已提交
906
	raw_spin_lock_irqsave(&rnp->lock, flags);
907
	delta = jiffies - ACCESS_ONCE(rsp->jiffies_stall);
908
	if (delta < RCU_STALL_RAT_DELAY || !rcu_gp_in_progress(rsp)) {
P
Paul E. McKenney 已提交
909
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
910 911
		return;
	}
912
	ACCESS_ONCE(rsp->jiffies_stall) = jiffies + 3 * rcu_jiffies_till_stall_check() + 3;
P
Paul E. McKenney 已提交
913
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
914

915 916 917 918 919
	/*
	 * OK, time to rat on our buddy...
	 * See Documentation/RCU/stallwarn.txt for info on how to debug
	 * RCU CPU stall warnings.
	 */
920
	pr_err("INFO: %s detected stalls on CPUs/tasks:",
921
	       rsp->name);
922
	print_cpu_stall_info_begin();
923
	rcu_for_each_leaf_node(rsp, rnp) {
924
		raw_spin_lock_irqsave(&rnp->lock, flags);
925
		ndetected += rcu_print_task_stall(rnp);
926 927 928 929 930 931 932 933
		if (rnp->qsmask != 0) {
			for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
				if (rnp->qsmask & (1UL << cpu)) {
					print_cpu_stall_info(rsp,
							     rnp->grplo + cpu);
					ndetected++;
				}
		}
934
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
935
	}
936 937 938 939 940 941 942

	/*
	 * 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);
943
	ndetected += rcu_print_task_stall(rnp);
944 945 946
	raw_spin_unlock_irqrestore(&rnp->lock, flags);

	print_cpu_stall_info_end();
947 948
	for_each_possible_cpu(cpu)
		totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen;
949
	pr_cont("(detected by %d, t=%ld jiffies, g=%ld, c=%ld, q=%lu)\n",
950
	       smp_processor_id(), (long)(jiffies - rsp->gp_start),
951
	       (long)rsp->gpnum, (long)rsp->completed, totqlen);
952
	if (ndetected == 0)
953
		pr_err("INFO: Stall ended before state dump start\n");
954
	else if (!trigger_all_cpu_backtrace())
955
		rcu_dump_cpu_stacks(rsp);
956

957
	/* Complain about tasks blocking the grace period. */
958 959 960

	rcu_print_detail_task_stall(rsp);

961
	force_quiescent_state(rsp);  /* Kick them all. */
962 963
}

964 965 966 967 968 969
/*
 * This function really isn't for public consumption, but RCU is special in
 * that context switches can allow the state machine to make progress.
 */
extern void resched_cpu(int cpu);

970 971
static void print_cpu_stall(struct rcu_state *rsp)
{
972
	int cpu;
973 974
	unsigned long flags;
	struct rcu_node *rnp = rcu_get_root(rsp);
975
	long totqlen = 0;
976

977 978 979 980 981
	/*
	 * OK, time to rat on ourselves...
	 * See Documentation/RCU/stallwarn.txt for info on how to debug
	 * RCU CPU stall warnings.
	 */
982
	pr_err("INFO: %s self-detected stall on CPU", rsp->name);
983 984 985
	print_cpu_stall_info_begin();
	print_cpu_stall_info(rsp, smp_processor_id());
	print_cpu_stall_info_end();
986 987
	for_each_possible_cpu(cpu)
		totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen;
988 989 990
	pr_cont(" (t=%lu jiffies g=%ld c=%ld q=%lu)\n",
		jiffies - rsp->gp_start,
		(long)rsp->gpnum, (long)rsp->completed, totqlen);
991 992
	if (!trigger_all_cpu_backtrace())
		dump_stack();
993

P
Paul E. McKenney 已提交
994
	raw_spin_lock_irqsave(&rnp->lock, flags);
995 996
	if (ULONG_CMP_GE(jiffies, ACCESS_ONCE(rsp->jiffies_stall)))
		ACCESS_ONCE(rsp->jiffies_stall) = jiffies +
997
				     3 * rcu_jiffies_till_stall_check() + 3;
P
Paul E. McKenney 已提交
998
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
999

1000 1001 1002 1003 1004 1005 1006 1007
	/*
	 * Attempt to revive the RCU machinery by forcing a context switch.
	 *
	 * A context switch would normally allow the RCU state machine to make
	 * progress and it could be we're stuck in kernel space without context
	 * switches for an entirely unreasonable amount of time.
	 */
	resched_cpu(smp_processor_id());
1008 1009 1010 1011
}

static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
{
1012 1013 1014
	unsigned long completed;
	unsigned long gpnum;
	unsigned long gps;
1015 1016
	unsigned long j;
	unsigned long js;
1017 1018
	struct rcu_node *rnp;

1019
	if (rcu_cpu_stall_suppress || !rcu_gp_in_progress(rsp))
1020
		return;
1021
	j = jiffies;
1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041

	/*
	 * Lots of memory barriers to reject false positives.
	 *
	 * The idea is to pick up rsp->gpnum, then rsp->jiffies_stall,
	 * then rsp->gp_start, and finally rsp->completed.  These values
	 * are updated in the opposite order with memory barriers (or
	 * equivalent) during grace-period initialization and cleanup.
	 * Now, a false positive can occur if we get an new value of
	 * rsp->gp_start and a old value of rsp->jiffies_stall.  But given
	 * the memory barriers, the only way that this can happen is if one
	 * grace period ends and another starts between these two fetches.
	 * Detect this by comparing rsp->completed with the previous fetch
	 * from rsp->gpnum.
	 *
	 * Given this check, comparisons of jiffies, rsp->jiffies_stall,
	 * and rsp->gp_start suffice to forestall false positives.
	 */
	gpnum = ACCESS_ONCE(rsp->gpnum);
	smp_rmb(); /* Pick up ->gpnum first... */
1042
	js = ACCESS_ONCE(rsp->jiffies_stall);
1043 1044 1045 1046 1047 1048 1049 1050
	smp_rmb(); /* ...then ->jiffies_stall before the rest... */
	gps = ACCESS_ONCE(rsp->gp_start);
	smp_rmb(); /* ...and finally ->gp_start before ->completed. */
	completed = ACCESS_ONCE(rsp->completed);
	if (ULONG_CMP_GE(completed, gpnum) ||
	    ULONG_CMP_LT(j, js) ||
	    ULONG_CMP_GE(gps, js))
		return; /* No stall or GP completed since entering function. */
1051
	rnp = rdp->mynode;
1052
	if (rcu_gp_in_progress(rsp) &&
1053
	    (ACCESS_ONCE(rnp->qsmask) & rdp->grpmask)) {
1054 1055 1056 1057

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

1058 1059
	} else if (rcu_gp_in_progress(rsp) &&
		   ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY)) {
1060

1061
		/* They had a few time units to dump stack, so complain. */
1062 1063 1064 1065
		print_other_cpu_stall(rsp);
	}
}

1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076
/**
 * 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)
{
1077 1078 1079
	struct rcu_state *rsp;

	for_each_rcu_flavor(rsp)
1080
		ACCESS_ONCE(rsp->jiffies_stall) = jiffies + ULONG_MAX / 2;
1081 1082
}

1083 1084 1085 1086 1087 1088 1089
/*
 * Initialize the specified rcu_data structure's callback list to empty.
 */
static void init_callback_list(struct rcu_data *rdp)
{
	int i;

1090 1091
	if (init_nocb_callback_list(rdp))
		return;
1092 1093 1094 1095 1096
	rdp->nxtlist = NULL;
	for (i = 0; i < RCU_NEXT_SIZE; i++)
		rdp->nxttail[i] = &rdp->nxtlist;
}

1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125
/*
 * Determine the value that ->completed will have at the end of the
 * next subsequent grace period.  This is used to tag callbacks so that
 * a CPU can invoke callbacks in a timely fashion even if that CPU has
 * been dyntick-idle for an extended period with callbacks under the
 * influence of RCU_FAST_NO_HZ.
 *
 * The caller must hold rnp->lock with interrupts disabled.
 */
static unsigned long rcu_cbs_completed(struct rcu_state *rsp,
				       struct rcu_node *rnp)
{
	/*
	 * If RCU is idle, we just wait for the next grace period.
	 * But we can only be sure that RCU is idle if we are looking
	 * at the root rcu_node structure -- otherwise, a new grace
	 * period might have started, but just not yet gotten around
	 * to initializing the current non-root rcu_node structure.
	 */
	if (rcu_get_root(rsp) == rnp && rnp->gpnum == rnp->completed)
		return rnp->completed + 1;

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

1126 1127 1128 1129 1130
/*
 * Trace-event helper function for rcu_start_future_gp() and
 * rcu_nocb_wait_gp().
 */
static void trace_rcu_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
1131
				unsigned long c, const char *s)
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
{
	trace_rcu_future_grace_period(rdp->rsp->name, rnp->gpnum,
				      rnp->completed, c, rnp->level,
				      rnp->grplo, rnp->grphi, s);
}

/*
 * Start some future grace period, as needed to handle newly arrived
 * callbacks.  The required future grace periods are recorded in each
 * rcu_node structure's ->need_future_gp field.
 *
 * The caller must hold the specified rcu_node structure's ->lock.
 */
static unsigned long __maybe_unused
rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp)
{
	unsigned long c;
	int i;
	struct rcu_node *rnp_root = rcu_get_root(rdp->rsp);

	/*
	 * Pick up grace-period number for new callbacks.  If this
	 * grace period is already marked as needed, return to the caller.
	 */
	c = rcu_cbs_completed(rdp->rsp, rnp);
1157
	trace_rcu_future_gp(rnp, rdp, c, TPS("Startleaf"));
1158
	if (rnp->need_future_gp[c & 0x1]) {
1159
		trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartleaf"));
1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172
		return c;
	}

	/*
	 * If either this rcu_node structure or the root rcu_node structure
	 * believe that a grace period is in progress, then we must wait
	 * for the one following, which is in "c".  Because our request
	 * will be noticed at the end of the current grace period, we don't
	 * need to explicitly start one.
	 */
	if (rnp->gpnum != rnp->completed ||
	    ACCESS_ONCE(rnp->gpnum) != ACCESS_ONCE(rnp->completed)) {
		rnp->need_future_gp[c & 0x1]++;
1173
		trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleaf"));
1174 1175 1176 1177 1178 1179 1180 1181
		return c;
	}

	/*
	 * There might be no grace period in progress.  If we don't already
	 * hold it, acquire the root rcu_node structure's lock in order to
	 * start one (if needed).
	 */
1182
	if (rnp != rnp_root) {
1183
		raw_spin_lock(&rnp_root->lock);
1184 1185
		smp_mb__after_unlock_lock();
	}
1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202

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

	/*
	 * If the needed for the required grace period is already
	 * recorded, trace and leave.
	 */
	if (rnp_root->need_future_gp[c & 0x1]) {
1203
		trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartedroot"));
1204 1205 1206 1207 1208 1209 1210 1211
		goto unlock_out;
	}

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

	/* If a grace period is not already in progress, start one. */
	if (rnp_root->gpnum != rnp_root->completed) {
1212
		trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleafroot"));
1213
	} else {
1214
		trace_rcu_future_gp(rnp, rdp, c, TPS("Startedroot"));
1215
		rcu_start_gp_advanced(rdp->rsp, rnp_root, rdp);
1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237
	}
unlock_out:
	if (rnp != rnp_root)
		raw_spin_unlock(&rnp_root->lock);
	return c;
}

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

	rcu_nocb_gp_cleanup(rsp, rnp);
	rnp->need_future_gp[c & 0x1] = 0;
	needmore = rnp->need_future_gp[(c + 1) & 0x1];
1238 1239
	trace_rcu_future_gp(rnp, rdp, c,
			    needmore ? TPS("CleanupMore") : TPS("Cleanup"));
1240 1241 1242
	return needmore;
}

1243 1244 1245 1246 1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 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 1292 1293 1294 1295 1296 1297 1298 1299 1300 1301
/*
 * If there is room, assign a ->completed number to any callbacks on
 * this CPU that have not already been assigned.  Also accelerate any
 * callbacks that were previously assigned a ->completed number that has
 * since proven to be too conservative, which can happen if callbacks get
 * assigned a ->completed number while RCU is idle, but with reference to
 * a non-root rcu_node structure.  This function is idempotent, so it does
 * not hurt to call it repeatedly.
 *
 * The caller must hold rnp->lock with interrupts disabled.
 */
static void rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
			       struct rcu_data *rdp)
{
	unsigned long c;
	int i;

	/* If the CPU has no callbacks, nothing to do. */
	if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL])
		return;

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

	/*
	 * If there are no sublist for unassigned callbacks, leave.
	 * At the same time, advance "i" one sublist, so that "i" will
	 * index into the sublist where all the remaining callbacks should
	 * be grouped into.
	 */
	if (++i >= RCU_NEXT_TAIL)
		return;

	/*
	 * Assign all subsequent callbacks' ->completed number to the next
	 * full grace period and group them all in the sublist initially
	 * indexed by "i".
	 */
	for (; i <= RCU_NEXT_TAIL; i++) {
		rdp->nxttail[i] = rdp->nxttail[RCU_NEXT_TAIL];
		rdp->nxtcompleted[i] = c;
	}
1302 1303
	/* Record any needed additional grace periods. */
	rcu_start_future_gp(rnp, rdp);
1304 1305 1306

	/* Trace depending on how much we were able to accelerate. */
	if (!*rdp->nxttail[RCU_WAIT_TAIL])
1307
		trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccWaitCB"));
1308
	else
1309
		trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccReadyCB"));
1310 1311 1312 1313 1314 1315 1316 1317 1318 1319 1320 1321 1322 1323 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
}

/*
 * Move any callbacks whose grace period has completed to the
 * RCU_DONE_TAIL sublist, then compact the remaining sublists and
 * assign ->completed numbers to any callbacks in the RCU_NEXT_TAIL
 * sublist.  This function is idempotent, so it does not hurt to
 * invoke it repeatedly.  As long as it is not invoked -too- often...
 *
 * The caller must hold rnp->lock with interrupts disabled.
 */
static void rcu_advance_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
			    struct rcu_data *rdp)
{
	int i, j;

	/* If the CPU has no callbacks, nothing to do. */
	if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL])
		return;

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

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

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

1355
/*
1356 1357 1358
 * Update CPU-local rcu_data state to record the beginnings and ends of
 * grace periods.  The caller must hold the ->lock of the leaf rcu_node
 * structure corresponding to the current CPU, and must have irqs disabled.
1359
 */
1360
static void __note_gp_changes(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
1361
{
1362
	/* Handle the ends of any preceding grace periods first. */
1363
	if (rdp->completed == rnp->completed) {
1364

1365
		/* No grace period end, so just accelerate recent callbacks. */
1366
		rcu_accelerate_cbs(rsp, rnp, rdp);
1367

1368 1369 1370 1371
	} else {

		/* Advance callbacks. */
		rcu_advance_cbs(rsp, rnp, rdp);
1372 1373 1374

		/* Remember that we saw this grace-period completion. */
		rdp->completed = rnp->completed;
1375
		trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuend"));
1376
	}
1377

1378 1379 1380 1381 1382 1383 1384
	if (rdp->gpnum != rnp->gpnum) {
		/*
		 * If the current grace period is waiting for this CPU,
		 * set up to detect a quiescent state, otherwise don't
		 * go looking for one.
		 */
		rdp->gpnum = rnp->gpnum;
1385
		trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpustart"));
1386 1387 1388 1389 1390 1391
		rdp->passed_quiesce = 0;
		rdp->qs_pending = !!(rnp->qsmask & rdp->grpmask);
		zero_cpu_stall_ticks(rdp);
	}
}

1392
static void note_gp_changes(struct rcu_state *rsp, struct rcu_data *rdp)
1393 1394 1395 1396 1397 1398
{
	unsigned long flags;
	struct rcu_node *rnp;

	local_irq_save(flags);
	rnp = rdp->mynode;
1399 1400
	if ((rdp->gpnum == ACCESS_ONCE(rnp->gpnum) &&
	     rdp->completed == ACCESS_ONCE(rnp->completed)) || /* w/out lock. */
1401 1402 1403 1404
	    !raw_spin_trylock(&rnp->lock)) { /* irqs already off, so later. */
		local_irq_restore(flags);
		return;
	}
1405
	smp_mb__after_unlock_lock();
1406
	__note_gp_changes(rsp, rnp, rdp);
1407 1408 1409
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
}

1410
/*
1411
 * Initialize a new grace period.  Return 0 if no grace period required.
1412
 */
1413
static int rcu_gp_init(struct rcu_state *rsp)
1414 1415
{
	struct rcu_data *rdp;
1416
	struct rcu_node *rnp = rcu_get_root(rsp);
1417

1418
	rcu_bind_gp_kthread();
1419
	raw_spin_lock_irq(&rnp->lock);
1420
	smp_mb__after_unlock_lock();
1421
	if (!ACCESS_ONCE(rsp->gp_flags)) {
1422 1423 1424 1425
		/* Spurious wakeup, tell caller to go back to sleep.  */
		raw_spin_unlock_irq(&rnp->lock);
		return 0;
	}
1426
	ACCESS_ONCE(rsp->gp_flags) = 0; /* Clear all flags: New grace period. */
1427

1428 1429 1430 1431 1432
	if (WARN_ON_ONCE(rcu_gp_in_progress(rsp))) {
		/*
		 * Grace period already in progress, don't start another.
		 * Not supposed to be able to happen.
		 */
1433 1434 1435 1436 1437
		raw_spin_unlock_irq(&rnp->lock);
		return 0;
	}

	/* Advance to a new grace period and initialize state. */
1438
	record_gp_stall_check_time(rsp);
1439 1440
	/* Record GP times before starting GP, hence smp_store_release(). */
	smp_store_release(&rsp->gpnum, rsp->gpnum + 1);
1441
	trace_rcu_grace_period(rsp->name, rsp->gpnum, TPS("start"));
1442 1443 1444
	raw_spin_unlock_irq(&rnp->lock);

	/* Exclude any concurrent CPU-hotplug operations. */
1445
	mutex_lock(&rsp->onoff_mutex);
1446
	smp_mb__after_unlock_lock(); /* ->gpnum increment before GP! */
1447 1448 1449 1450 1451 1452 1453 1454 1455 1456 1457 1458 1459 1460 1461

	/*
	 * Set the quiescent-state-needed bits in all the rcu_node
	 * structures for all currently online CPUs in breadth-first order,
	 * starting from the root rcu_node structure, relying on the layout
	 * of the tree within the rsp->node[] array.  Note that other CPUs
	 * will access only the leaves of the hierarchy, thus seeing that no
	 * grace period is in progress, at least until the corresponding
	 * leaf node has been initialized.  In addition, we have excluded
	 * CPU-hotplug operations.
	 *
	 * The grace period cannot complete until the initialization
	 * process finishes, because this kthread handles both.
	 */
	rcu_for_each_node_breadth_first(rsp, rnp) {
1462
		raw_spin_lock_irq(&rnp->lock);
1463
		smp_mb__after_unlock_lock();
1464
		rdp = this_cpu_ptr(rsp->rda);
1465 1466
		rcu_preempt_check_blocked_tasks(rnp);
		rnp->qsmask = rnp->qsmaskinit;
1467
		ACCESS_ONCE(rnp->gpnum) = rsp->gpnum;
1468
		WARN_ON_ONCE(rnp->completed != rsp->completed);
1469
		ACCESS_ONCE(rnp->completed) = rsp->completed;
1470
		if (rnp == rdp->mynode)
1471
			__note_gp_changes(rsp, rnp, rdp);
1472 1473 1474 1475 1476
		rcu_preempt_boost_start_gp(rnp);
		trace_rcu_grace_period_init(rsp->name, rnp->gpnum,
					    rnp->level, rnp->grplo,
					    rnp->grphi, rnp->qsmask);
		raw_spin_unlock_irq(&rnp->lock);
1477
#ifdef CONFIG_PROVE_RCU_DELAY
1478
		if ((prandom_u32() % (rcu_num_nodes + 1)) == 0 &&
1479
		    system_state == SYSTEM_RUNNING)
1480
			udelay(200);
1481
#endif /* #ifdef CONFIG_PROVE_RCU_DELAY */
1482 1483
		cond_resched();
	}
1484

1485
	mutex_unlock(&rsp->onoff_mutex);
1486 1487
	return 1;
}
1488

1489 1490 1491
/*
 * Do one round of quiescent-state forcing.
 */
1492
static int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in)
1493 1494
{
	int fqs_state = fqs_state_in;
1495 1496
	bool isidle = false;
	unsigned long maxj;
1497 1498 1499 1500 1501
	struct rcu_node *rnp = rcu_get_root(rsp);

	rsp->n_force_qs++;
	if (fqs_state == RCU_SAVE_DYNTICK) {
		/* Collect dyntick-idle snapshots. */
1502 1503 1504 1505
		if (is_sysidle_rcu_state(rsp)) {
			isidle = 1;
			maxj = jiffies - ULONG_MAX / 4;
		}
1506 1507
		force_qs_rnp(rsp, dyntick_save_progress_counter,
			     &isidle, &maxj);
1508
		rcu_sysidle_report_gp(rsp, isidle, maxj);
1509 1510 1511
		fqs_state = RCU_FORCE_QS;
	} else {
		/* Handle dyntick-idle and offline CPUs. */
1512
		isidle = 0;
1513
		force_qs_rnp(rsp, rcu_implicit_dynticks_qs, &isidle, &maxj);
1514 1515 1516 1517
	}
	/* Clear flag to prevent immediate re-entry. */
	if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
		raw_spin_lock_irq(&rnp->lock);
1518
		smp_mb__after_unlock_lock();
1519
		ACCESS_ONCE(rsp->gp_flags) &= ~RCU_GP_FLAG_FQS;
1520 1521 1522 1523 1524
		raw_spin_unlock_irq(&rnp->lock);
	}
	return fqs_state;
}

1525 1526 1527
/*
 * Clean up after the old grace period.
 */
1528
static void rcu_gp_cleanup(struct rcu_state *rsp)
1529 1530
{
	unsigned long gp_duration;
1531
	int nocb = 0;
1532 1533
	struct rcu_data *rdp;
	struct rcu_node *rnp = rcu_get_root(rsp);
1534

1535
	raw_spin_lock_irq(&rnp->lock);
1536
	smp_mb__after_unlock_lock();
1537 1538 1539
	gp_duration = jiffies - rsp->gp_start;
	if (gp_duration > rsp->gp_max)
		rsp->gp_max = gp_duration;
1540

1541 1542 1543 1544 1545 1546 1547 1548
	/*
	 * 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.
	 */
1549
	raw_spin_unlock_irq(&rnp->lock);
1550

1551 1552 1553 1554 1555 1556 1557 1558 1559 1560
	/*
	 * Propagate new ->completed value to rcu_node structures so
	 * that other CPUs don't have to wait until the start of the next
	 * grace period to process their callbacks.  This also avoids
	 * some nasty RCU grace-period initialization races by forcing
	 * the end of the current grace period to be completely recorded in
	 * all of the rcu_node structures before the beginning of the next
	 * grace period is recorded in any of the rcu_node structures.
	 */
	rcu_for_each_node_breadth_first(rsp, rnp) {
1561
		raw_spin_lock_irq(&rnp->lock);
1562
		smp_mb__after_unlock_lock();
1563
		ACCESS_ONCE(rnp->completed) = rsp->gpnum;
1564 1565
		rdp = this_cpu_ptr(rsp->rda);
		if (rnp == rdp->mynode)
1566
			__note_gp_changes(rsp, rnp, rdp);
1567
		/* smp_mb() provided by prior unlock-lock pair. */
1568
		nocb += rcu_future_gp_cleanup(rsp, rnp);
1569 1570
		raw_spin_unlock_irq(&rnp->lock);
		cond_resched();
1571
	}
1572 1573
	rnp = rcu_get_root(rsp);
	raw_spin_lock_irq(&rnp->lock);
1574
	smp_mb__after_unlock_lock(); /* Order GP before ->completed update. */
1575
	rcu_nocb_gp_set(rnp, nocb);
1576

1577 1578
	/* Declare grace period done. */
	ACCESS_ONCE(rsp->completed) = rsp->gpnum;
1579
	trace_rcu_grace_period(rsp->name, rsp->completed, TPS("end"));
1580
	rsp->fqs_state = RCU_GP_IDLE;
1581
	rdp = this_cpu_ptr(rsp->rda);
1582
	rcu_advance_cbs(rsp, rnp, rdp);  /* Reduce false positives below. */
1583
	if (cpu_needs_another_gp(rsp, rdp)) {
1584
		ACCESS_ONCE(rsp->gp_flags) = RCU_GP_FLAG_INIT;
1585 1586 1587 1588
		trace_rcu_grace_period(rsp->name,
				       ACCESS_ONCE(rsp->gpnum),
				       TPS("newreq"));
	}
1589 1590 1591 1592 1593 1594 1595 1596
	raw_spin_unlock_irq(&rnp->lock);
}

/*
 * Body of kthread that handles grace periods.
 */
static int __noreturn rcu_gp_kthread(void *arg)
{
1597
	int fqs_state;
1598
	int gf;
1599
	unsigned long j;
1600
	int ret;
1601 1602 1603 1604 1605 1606 1607
	struct rcu_state *rsp = arg;
	struct rcu_node *rnp = rcu_get_root(rsp);

	for (;;) {

		/* Handle grace-period start. */
		for (;;) {
1608 1609 1610
			trace_rcu_grace_period(rsp->name,
					       ACCESS_ONCE(rsp->gpnum),
					       TPS("reqwait"));
1611
			wait_event_interruptible(rsp->gp_wq,
1612
						 ACCESS_ONCE(rsp->gp_flags) &
1613
						 RCU_GP_FLAG_INIT);
1614
			/* Locking provides needed memory barrier. */
1615
			if (rcu_gp_init(rsp))
1616 1617 1618
				break;
			cond_resched();
			flush_signals(current);
1619 1620 1621
			trace_rcu_grace_period(rsp->name,
					       ACCESS_ONCE(rsp->gpnum),
					       TPS("reqwaitsig"));
1622
		}
1623

1624 1625
		/* Handle quiescent-state forcing. */
		fqs_state = RCU_SAVE_DYNTICK;
1626 1627 1628 1629 1630
		j = jiffies_till_first_fqs;
		if (j > HZ) {
			j = HZ;
			jiffies_till_first_fqs = HZ;
		}
1631
		ret = 0;
1632
		for (;;) {
1633 1634
			if (!ret)
				rsp->jiffies_force_qs = jiffies + j;
1635 1636 1637
			trace_rcu_grace_period(rsp->name,
					       ACCESS_ONCE(rsp->gpnum),
					       TPS("fqswait"));
1638
			ret = wait_event_interruptible_timeout(rsp->gp_wq,
1639 1640
					((gf = ACCESS_ONCE(rsp->gp_flags)) &
					 RCU_GP_FLAG_FQS) ||
1641 1642
					(!ACCESS_ONCE(rnp->qsmask) &&
					 !rcu_preempt_blocked_readers_cgp(rnp)),
1643
					j);
1644
			/* Locking provides needed memory barriers. */
1645
			/* If grace period done, leave loop. */
1646
			if (!ACCESS_ONCE(rnp->qsmask) &&
1647
			    !rcu_preempt_blocked_readers_cgp(rnp))
1648
				break;
1649
			/* If time for quiescent-state forcing, do it. */
1650 1651
			if (ULONG_CMP_GE(jiffies, rsp->jiffies_force_qs) ||
			    (gf & RCU_GP_FLAG_FQS)) {
1652 1653 1654
				trace_rcu_grace_period(rsp->name,
						       ACCESS_ONCE(rsp->gpnum),
						       TPS("fqsstart"));
1655
				fqs_state = rcu_gp_fqs(rsp, fqs_state);
1656 1657 1658
				trace_rcu_grace_period(rsp->name,
						       ACCESS_ONCE(rsp->gpnum),
						       TPS("fqsend"));
1659 1660 1661 1662 1663
				cond_resched();
			} else {
				/* Deal with stray signal. */
				cond_resched();
				flush_signals(current);
1664 1665 1666
				trace_rcu_grace_period(rsp->name,
						       ACCESS_ONCE(rsp->gpnum),
						       TPS("fqswaitsig"));
1667
			}
1668 1669 1670 1671 1672 1673 1674 1675
			j = jiffies_till_next_fqs;
			if (j > HZ) {
				j = HZ;
				jiffies_till_next_fqs = HZ;
			} else if (j < 1) {
				j = 1;
				jiffies_till_next_fqs = 1;
			}
1676
		}
1677 1678 1679

		/* Handle grace-period end. */
		rcu_gp_cleanup(rsp);
1680 1681 1682
	}
}

1683 1684 1685 1686 1687 1688
static void rsp_wakeup(struct irq_work *work)
{
	struct rcu_state *rsp = container_of(work, struct rcu_state, wakeup_work);

	/* Wake up rcu_gp_kthread() to start the grace period. */
	wake_up(&rsp->gp_wq);
1689 1690
	trace_rcu_grace_period(rsp->name, ACCESS_ONCE(rsp->gpnum),
			       "Workqueuewoken");
1691 1692
}

1693 1694 1695
/*
 * Start a new RCU grace period if warranted, re-initializing the hierarchy
 * in preparation for detecting the next grace period.  The caller must hold
1696
 * the root node's ->lock and hard irqs must be disabled.
1697 1698 1699 1700
 *
 * 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.
1701 1702
 */
static void
1703 1704
rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
		      struct rcu_data *rdp)
1705
{
1706
	if (!rsp->gp_kthread || !cpu_needs_another_gp(rsp, rdp)) {
1707
		/*
1708
		 * Either we have not yet spawned the grace-period
1709 1710
		 * task, this CPU does not need another grace period,
		 * or a grace period is already in progress.
1711
		 * Either way, don't start a new grace period.
1712 1713 1714
		 */
		return;
	}
1715
	ACCESS_ONCE(rsp->gp_flags) = RCU_GP_FLAG_INIT;
1716 1717
	trace_rcu_grace_period(rsp->name, ACCESS_ONCE(rsp->gpnum),
			       TPS("newreq"));
1718

1719 1720
	/*
	 * We can't do wakeups while holding the rnp->lock, as that
1721 1722 1723
	 * could cause possible deadlocks with the rq->lock. Defer
	 * the wakeup to interrupt context.  And don't bother waking
	 * up the running kthread.
1724
	 */
1725 1726 1727
	if (current != rsp->gp_kthread) {
		trace_rcu_grace_period(rsp->name, ACCESS_ONCE(rsp->gpnum),
				       "Workqueuewake");
1728
		irq_work_queue(&rsp->wakeup_work);
1729
	}
1730 1731
}

1732 1733 1734 1735 1736 1737 1738 1739 1740 1741 1742 1743 1744 1745 1746 1747 1748 1749 1750 1751 1752 1753 1754 1755 1756
/*
 * Similar to rcu_start_gp_advanced(), but also advance the calling CPU's
 * callbacks.  Note that rcu_start_gp_advanced() cannot do this because it
 * is invoked indirectly from rcu_advance_cbs(), which would result in
 * endless recursion -- or would do so if it wasn't for the self-deadlock
 * that is encountered beforehand.
 */
static void
rcu_start_gp(struct rcu_state *rsp)
{
	struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
	struct rcu_node *rnp = rcu_get_root(rsp);

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

1757
/*
P
Paul E. McKenney 已提交
1758 1759 1760
 * 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
1761 1762
 * if one is needed.  Note that the caller must hold rnp->lock, which
 * is released before return.
1763
 */
P
Paul E. McKenney 已提交
1764
static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
1765
	__releases(rcu_get_root(rsp)->lock)
1766
{
1767
	WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
1768 1769
	raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags);
	wake_up(&rsp->gp_wq);  /* Memory barrier implied by wake_up() path. */
1770 1771
}

1772
/*
P
Paul E. McKenney 已提交
1773 1774 1775 1776 1777 1778
 * 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.
1779 1780
 */
static void
P
Paul E. McKenney 已提交
1781 1782
rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
		  struct rcu_node *rnp, unsigned long flags)
1783 1784
	__releases(rnp->lock)
{
1785 1786
	struct rcu_node *rnp_c;

1787 1788 1789 1790 1791
	/* 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
1792
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
1793 1794 1795
			return;
		}
		rnp->qsmask &= ~mask;
1796 1797 1798 1799
		trace_rcu_quiescent_state_report(rsp->name, rnp->gpnum,
						 mask, rnp->qsmask, rnp->level,
						 rnp->grplo, rnp->grphi,
						 !!rnp->gp_tasks);
1800
		if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
1801 1802

			/* Other bits still set at this level, so done. */
P
Paul E. McKenney 已提交
1803
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
1804 1805 1806 1807 1808 1809 1810 1811 1812
			return;
		}
		mask = rnp->grpmask;
		if (rnp->parent == NULL) {

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

			break;
		}
P
Paul E. McKenney 已提交
1813
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
1814
		rnp_c = rnp;
1815
		rnp = rnp->parent;
P
Paul E. McKenney 已提交
1816
		raw_spin_lock_irqsave(&rnp->lock, flags);
1817
		smp_mb__after_unlock_lock();
1818
		WARN_ON_ONCE(rnp_c->qsmask);
1819 1820 1821 1822
	}

	/*
	 * Get here if we are the last CPU to pass through a quiescent
P
Paul E. McKenney 已提交
1823
	 * state for this grace period.  Invoke rcu_report_qs_rsp()
1824
	 * to clean up and start the next grace period if one is needed.
1825
	 */
P
Paul E. McKenney 已提交
1826
	rcu_report_qs_rsp(rsp, flags); /* releases rnp->lock. */
1827 1828 1829
}

/*
P
Paul E. McKenney 已提交
1830 1831 1832 1833 1834 1835 1836
 * 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!
1837 1838
 */
static void
1839
rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp)
1840 1841 1842 1843 1844 1845
{
	unsigned long flags;
	unsigned long mask;
	struct rcu_node *rnp;

	rnp = rdp->mynode;
P
Paul E. McKenney 已提交
1846
	raw_spin_lock_irqsave(&rnp->lock, flags);
1847
	smp_mb__after_unlock_lock();
1848 1849
	if (rdp->passed_quiesce == 0 || rdp->gpnum != rnp->gpnum ||
	    rnp->completed == rnp->gpnum) {
1850 1851

		/*
1852 1853 1854 1855
		 * 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.
1856
		 */
1857
		rdp->passed_quiesce = 0;	/* need qs for new gp. */
P
Paul E. McKenney 已提交
1858
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
1859 1860 1861 1862
		return;
	}
	mask = rdp->grpmask;
	if ((rnp->qsmask & mask) == 0) {
P
Paul E. McKenney 已提交
1863
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
1864 1865 1866 1867 1868 1869 1870
	} 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.
		 */
1871
		rcu_accelerate_cbs(rsp, rnp, rdp);
1872

P
Paul E. McKenney 已提交
1873
		rcu_report_qs_rnp(mask, rsp, rnp, flags); /* rlses rnp->lock */
1874 1875 1876 1877 1878 1879 1880 1881 1882 1883 1884 1885
	}
}

/*
 * 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)
{
1886 1887
	/* Check for grace-period ends and beginnings. */
	note_gp_changes(rsp, rdp);
1888 1889 1890 1891 1892 1893 1894 1895 1896 1897 1898 1899

	/*
	 * 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.
	 */
1900
	if (!rdp->passed_quiesce)
1901 1902
		return;

P
Paul E. McKenney 已提交
1903 1904 1905 1906
	/*
	 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
	 * judge of that).
	 */
1907
	rcu_report_qs_rdp(rdp->cpu, rsp, rdp);
1908 1909 1910 1911
}

#ifdef CONFIG_HOTPLUG_CPU

1912
/*
1913 1914
 * Send the specified CPU's RCU callbacks to the orphanage.  The
 * specified CPU must be offline, and the caller must hold the
1915
 * ->orphan_lock.
1916
 */
1917 1918 1919
static void
rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
			  struct rcu_node *rnp, struct rcu_data *rdp)
1920
{
P
Paul E. McKenney 已提交
1921
	/* No-CBs CPUs do not have orphanable callbacks. */
1922
	if (rcu_is_nocb_cpu(rdp->cpu))
P
Paul E. McKenney 已提交
1923 1924
		return;

1925 1926
	/*
	 * Orphan the callbacks.  First adjust the counts.  This is safe
1927 1928
	 * because _rcu_barrier() excludes CPU-hotplug operations, so it
	 * cannot be running now.  Thus no memory barrier is required.
1929
	 */
1930
	if (rdp->nxtlist != NULL) {
1931 1932 1933
		rsp->qlen_lazy += rdp->qlen_lazy;
		rsp->qlen += rdp->qlen;
		rdp->n_cbs_orphaned += rdp->qlen;
1934
		rdp->qlen_lazy = 0;
1935
		ACCESS_ONCE(rdp->qlen) = 0;
1936 1937 1938
	}

	/*
1939 1940 1941 1942 1943 1944 1945
	 * Next, move those callbacks still needing a grace period to
	 * the orphanage, where some other CPU will pick them up.
	 * Some of the callbacks might have gone partway through a grace
	 * period, but that is too bad.  They get to start over because we
	 * cannot assume that grace periods are synchronized across CPUs.
	 * We don't bother updating the ->nxttail[] array yet, instead
	 * we just reset the whole thing later on.
1946
	 */
1947 1948 1949 1950
	if (*rdp->nxttail[RCU_DONE_TAIL] != NULL) {
		*rsp->orphan_nxttail = *rdp->nxttail[RCU_DONE_TAIL];
		rsp->orphan_nxttail = rdp->nxttail[RCU_NEXT_TAIL];
		*rdp->nxttail[RCU_DONE_TAIL] = NULL;
1951 1952 1953
	}

	/*
1954 1955 1956
	 * Then move the ready-to-invoke callbacks to the orphanage,
	 * where some other CPU will pick them up.  These will not be
	 * required to pass though another grace period: They are done.
1957
	 */
1958
	if (rdp->nxtlist != NULL) {
1959 1960
		*rsp->orphan_donetail = rdp->nxtlist;
		rsp->orphan_donetail = rdp->nxttail[RCU_DONE_TAIL];
1961
	}
1962

1963
	/* Finally, initialize the rcu_data structure's list to empty.  */
1964
	init_callback_list(rdp);
1965 1966 1967 1968
}

/*
 * Adopt the RCU callbacks from the specified rcu_state structure's
1969
 * orphanage.  The caller must hold the ->orphan_lock.
1970
 */
1971
static void rcu_adopt_orphan_cbs(struct rcu_state *rsp, unsigned long flags)
1972 1973 1974 1975
{
	int i;
	struct rcu_data *rdp = __this_cpu_ptr(rsp->rda);

P
Paul E. McKenney 已提交
1976
	/* No-CBs CPUs are handled specially. */
1977
	if (rcu_nocb_adopt_orphan_cbs(rsp, rdp, flags))
P
Paul E. McKenney 已提交
1978 1979
		return;

1980 1981 1982 1983
	/* Do the accounting first. */
	rdp->qlen_lazy += rsp->qlen_lazy;
	rdp->qlen += rsp->qlen;
	rdp->n_cbs_adopted += rsp->qlen;
1984 1985
	if (rsp->qlen_lazy != rsp->qlen)
		rcu_idle_count_callbacks_posted();
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
	rsp->qlen_lazy = 0;
	rsp->qlen = 0;

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

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

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

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

	RCU_TRACE(mask = rdp->grpmask);
2025 2026
	trace_rcu_grace_period(rsp->name,
			       rnp->gpnum + 1 - !!(rnp->qsmask & mask),
2027
			       TPS("cpuofl"));
2028 2029 2030
}

/*
2031
 * The CPU has been completely removed, and some other CPU is reporting
2032 2033
 * this fact from process context.  Do the remainder of the cleanup,
 * including orphaning the outgoing CPU's RCU callbacks, and also
2034 2035
 * adopting them.  There can only be one CPU hotplug operation at a time,
 * so no other CPU can be attempting to update rcu_cpu_kthread_task.
2036
 */
2037
static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
2038
{
2039 2040 2041
	unsigned long flags;
	unsigned long mask;
	int need_report = 0;
2042
	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
2043
	struct rcu_node *rnp = rdp->mynode;  /* Outgoing CPU's rdp & rnp. */
2044

2045
	/* Adjust any no-longer-needed kthreads. */
T
Thomas Gleixner 已提交
2046
	rcu_boost_kthread_setaffinity(rnp, -1);
2047

2048
	/* Remove the dead CPU from the bitmasks in the rcu_node hierarchy. */
2049 2050

	/* Exclude any attempts to start a new grace period. */
2051
	mutex_lock(&rsp->onoff_mutex);
2052
	raw_spin_lock_irqsave(&rsp->orphan_lock, flags);
2053

2054 2055
	/* Orphan the dead CPU's callbacks, and adopt them if appropriate. */
	rcu_send_cbs_to_orphanage(cpu, rsp, rnp, rdp);
2056
	rcu_adopt_orphan_cbs(rsp, flags);
2057

2058 2059 2060 2061
	/* 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. */
2062
		smp_mb__after_unlock_lock();
2063 2064 2065 2066 2067 2068 2069 2070 2071 2072 2073 2074 2075 2076 2077 2078 2079
		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
2080
	 * because invoking rcu_report_unblock_qs_rnp() with ->orphan_lock
2081 2082
	 * held leads to deadlock.
	 */
2083
	raw_spin_unlock(&rsp->orphan_lock); /* irqs remain disabled. */
2084 2085 2086 2087 2088 2089 2090
	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);
2091 2092 2093
	WARN_ONCE(rdp->qlen != 0 || rdp->nxtlist != NULL,
		  "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, nxtlist=%p\n",
		  cpu, rdp->qlen, rdp->nxtlist);
2094 2095 2096
	init_callback_list(rdp);
	/* Disallow further callbacks on this CPU. */
	rdp->nxttail[RCU_NEXT_TAIL] = NULL;
2097
	mutex_unlock(&rsp->onoff_mutex);
2098 2099 2100 2101
}

#else /* #ifdef CONFIG_HOTPLUG_CPU */

2102
static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
2103 2104 2105
{
}

2106
static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
2107 2108 2109 2110 2111 2112 2113 2114 2115
{
}

#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.
 */
2116
static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
2117 2118 2119
{
	unsigned long flags;
	struct rcu_head *next, *list, **tail;
E
Eric Dumazet 已提交
2120 2121
	long bl, count, count_lazy;
	int i;
2122

2123
	/* If no callbacks are ready, just return. */
2124
	if (!cpu_has_callbacks_ready_to_invoke(rdp)) {
2125
		trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, 0);
2126 2127 2128
		trace_rcu_batch_end(rsp->name, 0, !!ACCESS_ONCE(rdp->nxtlist),
				    need_resched(), is_idle_task(current),
				    rcu_is_callbacks_kthread());
2129
		return;
2130
	}
2131 2132 2133 2134 2135 2136

	/*
	 * Extract the list of ready callbacks, disabling to prevent
	 * races with call_rcu() from interrupt handlers.
	 */
	local_irq_save(flags);
2137
	WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
2138
	bl = rdp->blimit;
2139
	trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, bl);
2140 2141 2142 2143
	list = rdp->nxtlist;
	rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
	*rdp->nxttail[RCU_DONE_TAIL] = NULL;
	tail = rdp->nxttail[RCU_DONE_TAIL];
2144 2145 2146
	for (i = RCU_NEXT_SIZE - 1; i >= 0; i--)
		if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
			rdp->nxttail[i] = &rdp->nxtlist;
2147 2148 2149
	local_irq_restore(flags);

	/* Invoke callbacks. */
2150
	count = count_lazy = 0;
2151 2152 2153
	while (list) {
		next = list->next;
		prefetch(next);
2154
		debug_rcu_head_unqueue(list);
2155 2156
		if (__rcu_reclaim(rsp->name, list))
			count_lazy++;
2157
		list = next;
2158 2159 2160 2161
		/* Stop only if limit reached and CPU has something to do. */
		if (++count >= bl &&
		    (need_resched() ||
		     (!is_idle_task(current) && !rcu_is_callbacks_kthread())))
2162 2163 2164 2165
			break;
	}

	local_irq_save(flags);
2166 2167 2168
	trace_rcu_batch_end(rsp->name, count, !!list, need_resched(),
			    is_idle_task(current),
			    rcu_is_callbacks_kthread());
2169 2170 2171 2172 2173

	/* Update count, and requeue any remaining callbacks. */
	if (list != NULL) {
		*tail = rdp->nxtlist;
		rdp->nxtlist = list;
2174 2175 2176
		for (i = 0; i < RCU_NEXT_SIZE; i++)
			if (&rdp->nxtlist == rdp->nxttail[i])
				rdp->nxttail[i] = tail;
2177 2178 2179
			else
				break;
	}
2180 2181
	smp_mb(); /* List handling before counting for rcu_barrier(). */
	rdp->qlen_lazy -= count_lazy;
2182
	ACCESS_ONCE(rdp->qlen) -= count;
2183
	rdp->n_cbs_invoked += count;
2184 2185 2186 2187 2188

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

2189 2190 2191 2192 2193 2194
	/* 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;
2195
	WARN_ON_ONCE((rdp->nxtlist == NULL) != (rdp->qlen == 0));
2196

2197 2198
	local_irq_restore(flags);

2199
	/* Re-invoke RCU core processing if there are callbacks remaining. */
2200
	if (cpu_has_callbacks_ready_to_invoke(rdp))
2201
		invoke_rcu_core();
2202 2203 2204 2205 2206
}

/*
 * 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).
2207
 * Also schedule RCU core processing.
2208
 *
2209
 * This function must be called from hardirq context.  It is normally
2210 2211 2212 2213 2214
 * 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)
{
2215
	trace_rcu_utilization(TPS("Start scheduler-tick"));
2216
	increment_cpu_stall_ticks();
2217
	if (user || rcu_is_cpu_rrupt_from_idle()) {
2218 2219 2220 2221 2222

		/*
		 * 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
2223
		 * a quiescent state, so note it.
2224 2225
		 *
		 * No memory barrier is required here because both
2226 2227 2228
		 * 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.
2229 2230
		 */

2231 2232
		rcu_sched_qs(cpu);
		rcu_bh_qs(cpu);
2233 2234 2235 2236 2237 2238 2239

	} 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
2240
		 * critical section, so note it.
2241 2242
		 */

2243
		rcu_bh_qs(cpu);
2244
	}
2245
	rcu_preempt_check_callbacks(cpu);
2246
	if (rcu_pending(cpu))
2247
		invoke_rcu_core();
2248
	trace_rcu_utilization(TPS("End scheduler-tick"));
2249 2250 2251 2252 2253
}

/*
 * Scan the leaf rcu_node structures, processing dyntick state for any that
 * have not yet encountered a quiescent state, using the function specified.
2254 2255
 * Also initiate boosting for any threads blocked on the root rcu_node.
 *
2256
 * The caller must have suppressed start of new grace periods.
2257
 */
2258 2259 2260 2261
static void force_qs_rnp(struct rcu_state *rsp,
			 int (*f)(struct rcu_data *rsp, bool *isidle,
				  unsigned long *maxj),
			 bool *isidle, unsigned long *maxj)
2262 2263 2264 2265 2266
{
	unsigned long bit;
	int cpu;
	unsigned long flags;
	unsigned long mask;
2267
	struct rcu_node *rnp;
2268

2269
	rcu_for_each_leaf_node(rsp, rnp) {
2270
		cond_resched();
2271
		mask = 0;
P
Paul E. McKenney 已提交
2272
		raw_spin_lock_irqsave(&rnp->lock, flags);
2273
		smp_mb__after_unlock_lock();
2274
		if (!rcu_gp_in_progress(rsp)) {
P
Paul E. McKenney 已提交
2275
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
2276
			return;
2277
		}
2278
		if (rnp->qsmask == 0) {
2279
			rcu_initiate_boost(rnp, flags); /* releases rnp->lock */
2280 2281
			continue;
		}
2282
		cpu = rnp->grplo;
2283
		bit = 1;
2284
		for (; cpu <= rnp->grphi; cpu++, bit <<= 1) {
2285 2286 2287 2288 2289 2290
			if ((rnp->qsmask & bit) != 0) {
				if ((rnp->qsmaskinit & bit) != 0)
					*isidle = 0;
				if (f(per_cpu_ptr(rsp->rda, cpu), isidle, maxj))
					mask |= bit;
			}
2291
		}
2292
		if (mask != 0) {
2293

P
Paul E. McKenney 已提交
2294 2295
			/* rcu_report_qs_rnp() releases rnp->lock. */
			rcu_report_qs_rnp(mask, rsp, rnp, flags);
2296 2297
			continue;
		}
P
Paul E. McKenney 已提交
2298
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
2299
	}
2300
	rnp = rcu_get_root(rsp);
2301 2302
	if (rnp->qsmask == 0) {
		raw_spin_lock_irqsave(&rnp->lock, flags);
2303
		smp_mb__after_unlock_lock();
2304 2305
		rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */
	}
2306 2307 2308 2309 2310 2311
}

/*
 * Force quiescent states on reluctant CPUs, and also detect which
 * CPUs are in dyntick-idle mode.
 */
2312
static void force_quiescent_state(struct rcu_state *rsp)
2313 2314
{
	unsigned long flags;
2315 2316 2317 2318 2319 2320 2321 2322 2323 2324 2325 2326
	bool ret;
	struct rcu_node *rnp;
	struct rcu_node *rnp_old = NULL;

	/* Funnel through hierarchy to reduce memory contention. */
	rnp = per_cpu_ptr(rsp->rda, raw_smp_processor_id())->mynode;
	for (; rnp != NULL; rnp = rnp->parent) {
		ret = (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) ||
		      !raw_spin_trylock(&rnp->fqslock);
		if (rnp_old != NULL)
			raw_spin_unlock(&rnp_old->fqslock);
		if (ret) {
2327
			ACCESS_ONCE(rsp->n_force_qs_lh)++;
2328 2329 2330 2331 2332
			return;
		}
		rnp_old = rnp;
	}
	/* rnp_old == rcu_get_root(rsp), rnp == NULL. */
2333

2334 2335
	/* Reached the root of the rcu_node tree, acquire lock. */
	raw_spin_lock_irqsave(&rnp_old->lock, flags);
2336
	smp_mb__after_unlock_lock();
2337 2338
	raw_spin_unlock(&rnp_old->fqslock);
	if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
2339
		ACCESS_ONCE(rsp->n_force_qs_lh)++;
2340
		raw_spin_unlock_irqrestore(&rnp_old->lock, flags);
2341
		return;  /* Someone beat us to it. */
2342
	}
2343
	ACCESS_ONCE(rsp->gp_flags) |= RCU_GP_FLAG_FQS;
2344
	raw_spin_unlock_irqrestore(&rnp_old->lock, flags);
2345
	wake_up(&rsp->gp_wq);  /* Memory barrier implied by wake_up() path. */
2346 2347 2348
}

/*
2349 2350 2351
 * 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.
2352 2353
 */
static void
2354
__rcu_process_callbacks(struct rcu_state *rsp)
2355 2356
{
	unsigned long flags;
2357
	struct rcu_data *rdp = __this_cpu_ptr(rsp->rda);
2358

2359 2360
	WARN_ON_ONCE(rdp->beenonline == 0);

2361 2362 2363 2364
	/* 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? */
2365
	local_irq_save(flags);
2366
	if (cpu_needs_another_gp(rsp, rdp)) {
2367
		raw_spin_lock(&rcu_get_root(rsp)->lock); /* irqs disabled. */
2368 2369
		rcu_start_gp(rsp);
		raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags);
2370 2371
	} else {
		local_irq_restore(flags);
2372 2373 2374
	}

	/* If there are callbacks ready, invoke them. */
2375
	if (cpu_has_callbacks_ready_to_invoke(rdp))
2376
		invoke_rcu_callbacks(rsp, rdp);
2377 2378 2379

	/* Do any needed deferred wakeups of rcuo kthreads. */
	do_nocb_deferred_wakeup(rdp);
2380 2381
}

2382
/*
2383
 * Do RCU core processing for the current CPU.
2384
 */
2385
static void rcu_process_callbacks(struct softirq_action *unused)
2386
{
2387 2388
	struct rcu_state *rsp;

2389 2390
	if (cpu_is_offline(smp_processor_id()))
		return;
2391
	trace_rcu_utilization(TPS("Start RCU core"));
2392 2393
	for_each_rcu_flavor(rsp)
		__rcu_process_callbacks(rsp);
2394
	trace_rcu_utilization(TPS("End RCU core"));
2395 2396
}

2397
/*
2398 2399 2400 2401 2402
 * 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.
2403
 */
2404
static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
2405
{
2406 2407
	if (unlikely(!ACCESS_ONCE(rcu_scheduler_fully_active)))
		return;
2408 2409
	if (likely(!rsp->boost)) {
		rcu_do_batch(rsp, rdp);
2410 2411
		return;
	}
2412
	invoke_rcu_callbacks_kthread();
2413 2414
}

2415
static void invoke_rcu_core(void)
2416
{
2417 2418
	if (cpu_online(smp_processor_id()))
		raise_softirq(RCU_SOFTIRQ);
2419 2420
}

2421 2422 2423 2424 2425
/*
 * Handle any core-RCU processing required by a call_rcu() invocation.
 */
static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
			    struct rcu_head *head, unsigned long flags)
2426
{
2427 2428 2429 2430
	/*
	 * If called from an extended quiescent state, invoke the RCU
	 * core in order to force a re-evaluation of RCU's idleness.
	 */
2431
	if (!rcu_is_watching() && cpu_online(smp_processor_id()))
2432 2433
		invoke_rcu_core();

2434
	/* If interrupts were disabled or CPU offline, don't invoke RCU core. */
2435
	if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
2436
		return;
2437

2438 2439 2440 2441 2442 2443 2444
	/*
	 * 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.
	 */
2445
	if (unlikely(rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) {
2446 2447

		/* Are we ignoring a completed grace period? */
2448
		note_gp_changes(rsp, rdp);
2449 2450 2451 2452 2453

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

2454
			raw_spin_lock(&rnp_root->lock);
2455
			smp_mb__after_unlock_lock();
2456 2457
			rcu_start_gp(rsp);
			raw_spin_unlock(&rnp_root->lock);
2458 2459 2460 2461 2462
		} 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)
2463
				force_quiescent_state(rsp);
2464 2465 2466
			rdp->n_force_qs_snap = rsp->n_force_qs;
			rdp->qlen_last_fqs_check = rdp->qlen;
		}
2467
	}
2468 2469
}

2470 2471 2472 2473 2474 2475 2476
/*
 * RCU callback function to leak a callback.
 */
static void rcu_leak_callback(struct rcu_head *rhp)
{
}

P
Paul E. McKenney 已提交
2477 2478 2479 2480 2481 2482
/*
 * Helper function for call_rcu() and friends.  The cpu argument will
 * normally be -1, indicating "currently running CPU".  It may specify
 * a CPU only if that CPU is a no-CBs CPU.  Currently, only _rcu_barrier()
 * is expected to specify a CPU.
 */
2483 2484
static void
__call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
P
Paul E. McKenney 已提交
2485
	   struct rcu_state *rsp, int cpu, bool lazy)
2486 2487 2488 2489
{
	unsigned long flags;
	struct rcu_data *rdp;

2490
	WARN_ON_ONCE((unsigned long)head & 0x3); /* Misaligned rcu_head! */
2491 2492 2493 2494 2495 2496
	if (debug_rcu_head_queue(head)) {
		/* Probable double call_rcu(), so leak the callback. */
		ACCESS_ONCE(head->func) = rcu_leak_callback;
		WARN_ONCE(1, "__call_rcu(): Leaked duplicate callback\n");
		return;
	}
2497 2498 2499 2500 2501 2502 2503 2504 2505 2506
	head->func = func;
	head->next = NULL;

	/*
	 * Opportunistically note grace-period endings and beginnings.
	 * Note that we might see a beginning right after we see an
	 * end, but never vice versa, since this CPU has to pass through
	 * a quiescent state betweentimes.
	 */
	local_irq_save(flags);
2507
	rdp = this_cpu_ptr(rsp->rda);
2508 2509

	/* Add the callback to our list. */
P
Paul E. McKenney 已提交
2510 2511 2512 2513 2514
	if (unlikely(rdp->nxttail[RCU_NEXT_TAIL] == NULL) || cpu != -1) {
		int offline;

		if (cpu != -1)
			rdp = per_cpu_ptr(rsp->rda, cpu);
2515
		offline = !__call_rcu_nocb(rdp, head, lazy, flags);
P
Paul E. McKenney 已提交
2516
		WARN_ON_ONCE(offline);
2517 2518 2519 2520
		/* _call_rcu() is illegal on offline CPU; leak the callback. */
		local_irq_restore(flags);
		return;
	}
2521
	ACCESS_ONCE(rdp->qlen)++;
2522 2523
	if (lazy)
		rdp->qlen_lazy++;
2524 2525
	else
		rcu_idle_count_callbacks_posted();
2526 2527 2528
	smp_mb();  /* Count before adding callback for rcu_barrier(). */
	*rdp->nxttail[RCU_NEXT_TAIL] = head;
	rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
2529

2530 2531
	if (__is_kfree_rcu_offset((unsigned long)func))
		trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func,
2532
					 rdp->qlen_lazy, rdp->qlen);
2533
	else
2534
		trace_rcu_callback(rsp->name, head, rdp->qlen_lazy, rdp->qlen);
2535

2536 2537
	/* Go handle any RCU core processing required. */
	__call_rcu_core(rsp, rdp, head, flags);
2538 2539 2540 2541
	local_irq_restore(flags);
}

/*
2542
 * Queue an RCU-sched callback for invocation after a grace period.
2543
 */
2544
void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
2545
{
P
Paul E. McKenney 已提交
2546
	__call_rcu(head, func, &rcu_sched_state, -1, 0);
2547
}
2548
EXPORT_SYMBOL_GPL(call_rcu_sched);
2549 2550

/*
2551
 * Queue an RCU callback for invocation after a quicker grace period.
2552 2553 2554
 */
void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
{
P
Paul E. McKenney 已提交
2555
	__call_rcu(head, func, &rcu_bh_state, -1, 0);
2556 2557 2558
}
EXPORT_SYMBOL_GPL(call_rcu_bh);

2559 2560 2561 2562 2563 2564 2565 2566 2567 2568 2569
/*
 * Because a context switch is a grace period for RCU-sched and RCU-bh,
 * any blocking grace-period wait automatically implies a grace period
 * if there is only one CPU online at any point time during execution
 * of either synchronize_sched() or synchronize_rcu_bh().  It is OK to
 * occasionally incorrectly indicate that there are multiple CPUs online
 * when there was in fact only one the whole time, as this just adds
 * some overhead: RCU still operates correctly.
 */
static inline int rcu_blocking_is_gp(void)
{
2570 2571
	int ret;

2572
	might_sleep();  /* Check for RCU read-side critical section. */
2573 2574 2575 2576
	preempt_disable();
	ret = num_online_cpus() <= 1;
	preempt_enable();
	return ret;
2577 2578
}

2579 2580 2581 2582 2583 2584 2585 2586 2587 2588 2589 2590
/**
 * 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
2591 2592 2593 2594 2595 2596 2597 2598 2599 2600 2601 2602 2603 2604 2605 2606 2607 2608 2609 2610 2611 2612
 * non-threaded hardware-interrupt handlers, in progress on entry will
 * have completed before this primitive returns.  However, this does not
 * guarantee that softirq handlers will have completed, since in some
 * kernels, these handlers can run in process context, and can block.
 *
 * Note that this guarantee implies further memory-ordering guarantees.
 * On systems with more than one CPU, when synchronize_sched() returns,
 * each CPU is guaranteed to have executed a full memory barrier since the
 * end of its last RCU-sched read-side critical section whose beginning
 * preceded the call to synchronize_sched().  In addition, each CPU having
 * an RCU read-side critical section that extends beyond the return from
 * synchronize_sched() is guaranteed to have executed a full memory barrier
 * after the beginning of synchronize_sched() and before the beginning of
 * that RCU read-side critical section.  Note that these guarantees include
 * CPUs that are offline, idle, or executing in user mode, as well as CPUs
 * that are executing in the kernel.
 *
 * Furthermore, if CPU A invoked synchronize_sched(), which returned
 * to its caller on CPU B, then both CPU A and CPU B are guaranteed
 * to have executed a full memory barrier during the execution of
 * synchronize_sched() -- even if CPU A and CPU B are the same CPU (but
 * again only if the system has more than one CPU).
2613 2614 2615 2616 2617 2618 2619 2620 2621
 *
 * 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)
{
2622 2623 2624 2625
	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");
2626 2627
	if (rcu_blocking_is_gp())
		return;
2628 2629 2630 2631
	if (rcu_expedited)
		synchronize_sched_expedited();
	else
		wait_rcu_gp(call_rcu_sched);
2632 2633 2634 2635 2636 2637 2638 2639 2640 2641 2642
}
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.
2643 2644 2645
 *
 * See the description of synchronize_sched() for more detailed information
 * on memory ordering guarantees.
2646 2647 2648
 */
void synchronize_rcu_bh(void)
{
2649 2650 2651 2652
	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");
2653 2654
	if (rcu_blocking_is_gp())
		return;
2655 2656 2657 2658
	if (rcu_expedited)
		synchronize_rcu_bh_expedited();
	else
		wait_rcu_gp(call_rcu_bh);
2659 2660 2661
}
EXPORT_SYMBOL_GPL(synchronize_rcu_bh);

2662 2663 2664 2665 2666 2667 2668 2669 2670 2671 2672 2673 2674 2675 2676 2677 2678 2679 2680 2681 2682 2683 2684 2685 2686 2687 2688 2689 2690 2691 2692 2693 2694 2695 2696 2697 2698 2699 2700 2701 2702 2703 2704 2705 2706 2707 2708 2709 2710 2711 2712 2713
/**
 * get_state_synchronize_rcu - Snapshot current RCU state
 *
 * Returns a cookie that is used by a later call to cond_synchronize_rcu()
 * to determine whether or not a full grace period has elapsed in the
 * meantime.
 */
unsigned long get_state_synchronize_rcu(void)
{
	/*
	 * Any prior manipulation of RCU-protected data must happen
	 * before the load from ->gpnum.
	 */
	smp_mb();  /* ^^^ */

	/*
	 * Make sure this load happens before the purportedly
	 * time-consuming work between get_state_synchronize_rcu()
	 * and cond_synchronize_rcu().
	 */
	return smp_load_acquire(&rcu_state->gpnum);
}
EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);

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

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

2714 2715 2716 2717 2718 2719 2720 2721 2722 2723 2724 2725 2726 2727 2728 2729 2730
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;
}

2731 2732 2733 2734 2735 2736 2737 2738 2739 2740
/**
 * 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.
2741
 *
2742 2743 2744 2745
 * 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.
2746 2747 2748 2749 2750 2751 2752 2753 2754 2755 2756 2757 2758 2759 2760 2761 2762 2763 2764 2765 2766 2767 2768 2769
 *
 * 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)
{
2770 2771
	long firstsnap, s, snap;
	int trycount = 0;
2772
	struct rcu_state *rsp = &rcu_sched_state;
2773

2774 2775 2776 2777 2778 2779 2780 2781
	/*
	 * If we are in danger of counter wrap, just do synchronize_sched().
	 * By allowing sync_sched_expedited_started to advance no more than
	 * ULONG_MAX/8 ahead of sync_sched_expedited_done, we are ensuring
	 * that more than 3.5 billion CPUs would be required to force a
	 * counter wrap on a 32-bit system.  Quite a few more CPUs would of
	 * course be required on a 64-bit system.
	 */
2782 2783
	if (ULONG_CMP_GE((ulong)atomic_long_read(&rsp->expedited_start),
			 (ulong)atomic_long_read(&rsp->expedited_done) +
2784 2785
			 ULONG_MAX / 8)) {
		synchronize_sched();
2786
		atomic_long_inc(&rsp->expedited_wrap);
2787 2788
		return;
	}
2789

2790 2791 2792 2793
	/*
	 * Take a ticket.  Note that atomic_inc_return() implies a
	 * full memory barrier.
	 */
2794
	snap = atomic_long_inc_return(&rsp->expedited_start);
2795
	firstsnap = snap;
2796
	get_online_cpus();
2797
	WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id()));
2798 2799 2800 2801 2802 2803 2804 2805 2806

	/*
	 * 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();
2807
		atomic_long_inc(&rsp->expedited_tryfail);
2808

2809
		/* Check to see if someone else did our work for us. */
2810
		s = atomic_long_read(&rsp->expedited_done);
2811
		if (ULONG_CMP_GE((ulong)s, (ulong)firstsnap)) {
2812 2813 2814
			/* ensure test happens before caller kfree */
			smp_mb__before_atomic_inc(); /* ^^^ */
			atomic_long_inc(&rsp->expedited_workdone1);
2815 2816
			return;
		}
2817 2818

		/* No joy, try again later.  Or just synchronize_sched(). */
2819
		if (trycount++ < 10) {
2820
			udelay(trycount * num_online_cpus());
2821
		} else {
2822
			wait_rcu_gp(call_rcu_sched);
2823
			atomic_long_inc(&rsp->expedited_normal);
2824 2825 2826
			return;
		}

2827
		/* Recheck to see if someone else did our work for us. */
2828
		s = atomic_long_read(&rsp->expedited_done);
2829
		if (ULONG_CMP_GE((ulong)s, (ulong)firstsnap)) {
2830 2831 2832
			/* ensure test happens before caller kfree */
			smp_mb__before_atomic_inc(); /* ^^^ */
			atomic_long_inc(&rsp->expedited_workdone2);
2833 2834 2835 2836 2837
			return;
		}

		/*
		 * Refetching sync_sched_expedited_started allows later
2838 2839 2840 2841
		 * callers to piggyback on our grace period.  We retry
		 * after they started, so our grace period works for them,
		 * and they started after our first try, so their grace
		 * period works for us.
2842 2843
		 */
		get_online_cpus();
2844
		snap = atomic_long_read(&rsp->expedited_start);
2845 2846
		smp_mb(); /* ensure read is before try_stop_cpus(). */
	}
2847
	atomic_long_inc(&rsp->expedited_stoppedcpus);
2848 2849 2850 2851 2852

	/*
	 * 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
2853
	 * than we did already did their update.
2854 2855
	 */
	do {
2856
		atomic_long_inc(&rsp->expedited_done_tries);
2857
		s = atomic_long_read(&rsp->expedited_done);
2858
		if (ULONG_CMP_GE((ulong)s, (ulong)snap)) {
2859 2860 2861
			/* ensure test happens before caller kfree */
			smp_mb__before_atomic_inc(); /* ^^^ */
			atomic_long_inc(&rsp->expedited_done_lost);
2862 2863
			break;
		}
2864
	} while (atomic_long_cmpxchg(&rsp->expedited_done, s, snap) != s);
2865
	atomic_long_inc(&rsp->expedited_done_exit);
2866 2867 2868 2869 2870

	put_online_cpus();
}
EXPORT_SYMBOL_GPL(synchronize_sched_expedited);

2871 2872 2873 2874 2875 2876 2877 2878 2879
/*
 * 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)
{
2880 2881
	struct rcu_node *rnp = rdp->mynode;

2882 2883 2884 2885 2886
	rdp->n_rcu_pending++;

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

2887 2888 2889 2890
	/* Is this CPU a NO_HZ_FULL CPU that should ignore RCU? */
	if (rcu_nohz_full_cpu(rsp))
		return 0;

2891
	/* Is the RCU core waiting for a quiescent state from this CPU? */
2892 2893
	if (rcu_scheduler_fully_active &&
	    rdp->qs_pending && !rdp->passed_quiesce) {
2894
		rdp->n_rp_qs_pending++;
2895
	} else if (rdp->qs_pending && rdp->passed_quiesce) {
2896
		rdp->n_rp_report_qs++;
2897
		return 1;
2898
	}
2899 2900

	/* Does this CPU have callbacks ready to invoke? */
2901 2902
	if (cpu_has_callbacks_ready_to_invoke(rdp)) {
		rdp->n_rp_cb_ready++;
2903
		return 1;
2904
	}
2905 2906

	/* Has RCU gone idle with this CPU needing another grace period? */
2907 2908
	if (cpu_needs_another_gp(rsp, rdp)) {
		rdp->n_rp_cpu_needs_gp++;
2909
		return 1;
2910
	}
2911 2912

	/* Has another RCU grace period completed?  */
2913
	if (ACCESS_ONCE(rnp->completed) != rdp->completed) { /* outside lock */
2914
		rdp->n_rp_gp_completed++;
2915
		return 1;
2916
	}
2917 2918

	/* Has a new RCU grace period started? */
2919
	if (ACCESS_ONCE(rnp->gpnum) != rdp->gpnum) { /* outside lock */
2920
		rdp->n_rp_gp_started++;
2921
		return 1;
2922
	}
2923

2924 2925 2926 2927 2928 2929
	/* Does this CPU need a deferred NOCB wakeup? */
	if (rcu_nocb_need_deferred_wakeup(rdp)) {
		rdp->n_rp_nocb_defer_wakeup++;
		return 1;
	}

2930
	/* nothing to do */
2931
	rdp->n_rp_need_nothing++;
2932 2933 2934 2935 2936 2937 2938 2939
	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.
 */
2940
static int rcu_pending(int cpu)
2941
{
2942 2943 2944 2945 2946 2947
	struct rcu_state *rsp;

	for_each_rcu_flavor(rsp)
		if (__rcu_pending(rsp, per_cpu_ptr(rsp->rda, cpu)))
			return 1;
	return 0;
2948 2949 2950
}

/*
2951 2952 2953
 * Return true if the specified CPU has any callback.  If all_lazy is
 * non-NULL, store an indication of whether all callbacks are lazy.
 * (If there are no callbacks, all of them are deemed to be lazy.)
2954
 */
2955
static int __maybe_unused rcu_cpu_has_callbacks(int cpu, bool *all_lazy)
2956
{
2957 2958 2959
	bool al = true;
	bool hc = false;
	struct rcu_data *rdp;
2960 2961
	struct rcu_state *rsp;

2962 2963
	for_each_rcu_flavor(rsp) {
		rdp = per_cpu_ptr(rsp->rda, cpu);
2964 2965 2966 2967
		if (!rdp->nxtlist)
			continue;
		hc = true;
		if (rdp->qlen != rdp->qlen_lazy || !all_lazy) {
2968
			al = false;
2969 2970
			break;
		}
2971 2972 2973 2974
	}
	if (all_lazy)
		*all_lazy = al;
	return hc;
2975 2976
}

2977 2978 2979 2980
/*
 * Helper function for _rcu_barrier() tracing.  If tracing is disabled,
 * the compiler is expected to optimize this away.
 */
2981
static void _rcu_barrier_trace(struct rcu_state *rsp, const char *s,
2982 2983 2984 2985 2986 2987
			       int cpu, unsigned long done)
{
	trace_rcu_barrier(rsp->name, s, cpu,
			  atomic_read(&rsp->barrier_cpu_count), done);
}

2988 2989 2990 2991
/*
 * RCU callback function for _rcu_barrier().  If we are last, wake
 * up the task executing _rcu_barrier().
 */
2992
static void rcu_barrier_callback(struct rcu_head *rhp)
2993
{
2994 2995 2996
	struct rcu_data *rdp = container_of(rhp, struct rcu_data, barrier_head);
	struct rcu_state *rsp = rdp->rsp;

2997 2998
	if (atomic_dec_and_test(&rsp->barrier_cpu_count)) {
		_rcu_barrier_trace(rsp, "LastCB", -1, rsp->n_barrier_done);
2999
		complete(&rsp->barrier_completion);
3000 3001 3002
	} else {
		_rcu_barrier_trace(rsp, "CB", -1, rsp->n_barrier_done);
	}
3003 3004 3005 3006 3007 3008 3009
}

/*
 * Called with preemption disabled, and from cross-cpu IRQ context.
 */
static void rcu_barrier_func(void *type)
{
3010
	struct rcu_state *rsp = type;
3011
	struct rcu_data *rdp = __this_cpu_ptr(rsp->rda);
3012

3013
	_rcu_barrier_trace(rsp, "IRQ", -1, rsp->n_barrier_done);
3014
	atomic_inc(&rsp->barrier_cpu_count);
3015
	rsp->call(&rdp->barrier_head, rcu_barrier_callback);
3016 3017 3018 3019 3020 3021
}

/*
 * Orchestrate the specified type of RCU barrier, waiting for all
 * RCU callbacks of the specified type to complete.
 */
3022
static void _rcu_barrier(struct rcu_state *rsp)
3023
{
3024 3025
	int cpu;
	struct rcu_data *rdp;
3026 3027
	unsigned long snap = ACCESS_ONCE(rsp->n_barrier_done);
	unsigned long snap_done;
3028

3029
	_rcu_barrier_trace(rsp, "Begin", -1, snap);
3030

3031
	/* Take mutex to serialize concurrent rcu_barrier() requests. */
3032
	mutex_lock(&rsp->barrier_mutex);
3033

3034 3035 3036 3037 3038 3039 3040 3041 3042 3043 3044 3045
	/*
	 * Ensure that all prior references, including to ->n_barrier_done,
	 * are ordered before the _rcu_barrier() machinery.
	 */
	smp_mb();  /* See above block comment. */

	/*
	 * Recheck ->n_barrier_done to see if others did our work for us.
	 * This means checking ->n_barrier_done for an even-to-odd-to-even
	 * transition.  The "if" expression below therefore rounds the old
	 * value up to the next even number and adds two before comparing.
	 */
3046
	snap_done = rsp->n_barrier_done;
3047
	_rcu_barrier_trace(rsp, "Check", -1, snap_done);
3048 3049 3050 3051 3052 3053 3054 3055 3056 3057 3058 3059

	/*
	 * If the value in snap is odd, we needed to wait for the current
	 * rcu_barrier() to complete, then wait for the next one, in other
	 * words, we need the value of snap_done to be three larger than
	 * the value of snap.  On the other hand, if the value in snap is
	 * even, we only had to wait for the next rcu_barrier() to complete,
	 * in other words, we need the value of snap_done to be only two
	 * greater than the value of snap.  The "(snap + 3) & ~0x1" computes
	 * this for us (thank you, Linus!).
	 */
	if (ULONG_CMP_GE(snap_done, (snap + 3) & ~0x1)) {
3060
		_rcu_barrier_trace(rsp, "EarlyExit", -1, snap_done);
3061 3062 3063 3064 3065 3066 3067 3068 3069 3070 3071 3072
		smp_mb(); /* caller's subsequent code after above check. */
		mutex_unlock(&rsp->barrier_mutex);
		return;
	}

	/*
	 * Increment ->n_barrier_done to avoid duplicate work.  Use
	 * ACCESS_ONCE() to prevent the compiler from speculating
	 * the increment to precede the early-exit check.
	 */
	ACCESS_ONCE(rsp->n_barrier_done)++;
	WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 1);
3073
	_rcu_barrier_trace(rsp, "Inc1", -1, rsp->n_barrier_done);
3074
	smp_mb(); /* Order ->n_barrier_done increment with below mechanism. */
3075

3076
	/*
3077 3078
	 * Initialize the count to one rather than to zero in order to
	 * avoid a too-soon return to zero in case of a short grace period
3079 3080
	 * (or preemption of this task).  Exclude CPU-hotplug operations
	 * to ensure that no offline CPU has callbacks queued.
3081
	 */
3082
	init_completion(&rsp->barrier_completion);
3083
	atomic_set(&rsp->barrier_cpu_count, 1);
3084
	get_online_cpus();
3085 3086

	/*
3087 3088 3089
	 * Force each CPU with callbacks to register a new callback.
	 * When that callback is invoked, we will know that all of the
	 * corresponding CPU's preceding callbacks have been invoked.
3090
	 */
P
Paul E. McKenney 已提交
3091
	for_each_possible_cpu(cpu) {
3092
		if (!cpu_online(cpu) && !rcu_is_nocb_cpu(cpu))
P
Paul E. McKenney 已提交
3093
			continue;
3094
		rdp = per_cpu_ptr(rsp->rda, cpu);
3095
		if (rcu_is_nocb_cpu(cpu)) {
P
Paul E. McKenney 已提交
3096 3097 3098 3099 3100 3101
			_rcu_barrier_trace(rsp, "OnlineNoCB", cpu,
					   rsp->n_barrier_done);
			atomic_inc(&rsp->barrier_cpu_count);
			__call_rcu(&rdp->barrier_head, rcu_barrier_callback,
				   rsp, cpu, 0);
		} else if (ACCESS_ONCE(rdp->qlen)) {
3102 3103
			_rcu_barrier_trace(rsp, "OnlineQ", cpu,
					   rsp->n_barrier_done);
3104
			smp_call_function_single(cpu, rcu_barrier_func, rsp, 1);
3105
		} else {
3106 3107
			_rcu_barrier_trace(rsp, "OnlineNQ", cpu,
					   rsp->n_barrier_done);
3108 3109
		}
	}
3110
	put_online_cpus();
3111 3112 3113 3114 3115

	/*
	 * Now that we have an rcu_barrier_callback() callback on each
	 * CPU, and thus each counted, remove the initial count.
	 */
3116
	if (atomic_dec_and_test(&rsp->barrier_cpu_count))
3117
		complete(&rsp->barrier_completion);
3118

3119 3120 3121 3122
	/* Increment ->n_barrier_done to prevent duplicate work. */
	smp_mb(); /* Keep increment after above mechanism. */
	ACCESS_ONCE(rsp->n_barrier_done)++;
	WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 0);
3123
	_rcu_barrier_trace(rsp, "Inc2", -1, rsp->n_barrier_done);
3124 3125
	smp_mb(); /* Keep increment before caller's subsequent code. */

3126
	/* Wait for all rcu_barrier_callback() callbacks to be invoked. */
3127
	wait_for_completion(&rsp->barrier_completion);
3128 3129

	/* Other rcu_barrier() invocations can now safely proceed. */
3130
	mutex_unlock(&rsp->barrier_mutex);
3131 3132 3133 3134 3135 3136 3137
}

/**
 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
 */
void rcu_barrier_bh(void)
{
3138
	_rcu_barrier(&rcu_bh_state);
3139 3140 3141 3142 3143 3144 3145 3146
}
EXPORT_SYMBOL_GPL(rcu_barrier_bh);

/**
 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
 */
void rcu_barrier_sched(void)
{
3147
	_rcu_barrier(&rcu_sched_state);
3148 3149 3150
}
EXPORT_SYMBOL_GPL(rcu_barrier_sched);

3151
/*
3152
 * Do boot-time initialization of a CPU's per-CPU RCU data.
3153
 */
3154 3155
static void __init
rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
3156 3157
{
	unsigned long flags;
3158
	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
3159 3160 3161
	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
3162
	raw_spin_lock_irqsave(&rnp->lock, flags);
3163
	rdp->grpmask = 1UL << (cpu - rdp->mynode->grplo);
3164
	init_callback_list(rdp);
3165
	rdp->qlen_lazy = 0;
3166
	ACCESS_ONCE(rdp->qlen) = 0;
3167
	rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
3168
	WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE);
3169
	WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1);
3170
	rdp->cpu = cpu;
3171
	rdp->rsp = rsp;
P
Paul E. McKenney 已提交
3172
	rcu_boot_init_nocb_percpu_data(rdp);
P
Paul E. McKenney 已提交
3173
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
3174 3175 3176 3177 3178 3179 3180
}

/*
 * 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.
3181
 */
3182
static void
3183
rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
3184 3185 3186
{
	unsigned long flags;
	unsigned long mask;
3187
	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
3188 3189
	struct rcu_node *rnp = rcu_get_root(rsp);

3190 3191 3192
	/* Exclude new grace periods. */
	mutex_lock(&rsp->onoff_mutex);

3193
	/* Set up local state, ensuring consistent view of global state. */
P
Paul E. McKenney 已提交
3194
	raw_spin_lock_irqsave(&rnp->lock, flags);
3195
	rdp->beenonline = 1;	 /* We have now been online. */
3196 3197
	rdp->qlen_last_fqs_check = 0;
	rdp->n_force_qs_snap = rsp->n_force_qs;
3198
	rdp->blimit = blimit;
3199
	init_callback_list(rdp);  /* Re-enable callbacks on this CPU. */
3200
	rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
3201
	rcu_sysidle_init_percpu_data(rdp->dynticks);
3202 3203
	atomic_set(&rdp->dynticks->dynticks,
		   (atomic_read(&rdp->dynticks->dynticks) & ~0x1) + 1);
P
Paul E. McKenney 已提交
3204
	raw_spin_unlock(&rnp->lock);		/* irqs remain disabled. */
3205 3206 3207 3208 3209 3210

	/* 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
3211
		raw_spin_lock(&rnp->lock);	/* irqs already disabled. */
3212 3213
		rnp->qsmaskinit |= mask;
		mask = rnp->grpmask;
3214
		if (rnp == rdp->mynode) {
3215 3216 3217 3218 3219 3220
			/*
			 * 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;
3221
			rdp->completed = rnp->completed;
3222 3223
			rdp->passed_quiesce = 0;
			rdp->qs_pending = 0;
3224
			trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuonl"));
3225
		}
P
Paul E. McKenney 已提交
3226
		raw_spin_unlock(&rnp->lock); /* irqs already disabled. */
3227 3228
		rnp = rnp->parent;
	} while (rnp != NULL && !(rnp->qsmaskinit & mask));
3229
	local_irq_restore(flags);
3230

3231
	mutex_unlock(&rsp->onoff_mutex);
3232 3233
}

3234
static void rcu_prepare_cpu(int cpu)
3235
{
3236 3237 3238
	struct rcu_state *rsp;

	for_each_rcu_flavor(rsp)
3239
		rcu_init_percpu_data(cpu, rsp);
3240 3241 3242
}

/*
3243
 * Handle CPU online/offline notification events.
3244
 */
3245
static int rcu_cpu_notify(struct notifier_block *self,
3246
				    unsigned long action, void *hcpu)
3247 3248
{
	long cpu = (long)hcpu;
3249
	struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
3250
	struct rcu_node *rnp = rdp->mynode;
3251
	struct rcu_state *rsp;
3252

3253
	trace_rcu_utilization(TPS("Start CPU hotplug"));
3254 3255 3256
	switch (action) {
	case CPU_UP_PREPARE:
	case CPU_UP_PREPARE_FROZEN:
P
Peter Zijlstra 已提交
3257 3258
		rcu_prepare_cpu(cpu);
		rcu_prepare_kthreads(cpu);
3259 3260
		break;
	case CPU_ONLINE:
3261
	case CPU_DOWN_FAILED:
T
Thomas Gleixner 已提交
3262
		rcu_boost_kthread_setaffinity(rnp, -1);
3263 3264
		break;
	case CPU_DOWN_PREPARE:
3265
		rcu_boost_kthread_setaffinity(rnp, cpu);
3266
		break;
3267 3268
	case CPU_DYING:
	case CPU_DYING_FROZEN:
3269 3270
		for_each_rcu_flavor(rsp)
			rcu_cleanup_dying_cpu(rsp);
3271
		break;
3272 3273 3274 3275
	case CPU_DEAD:
	case CPU_DEAD_FROZEN:
	case CPU_UP_CANCELED:
	case CPU_UP_CANCELED_FROZEN:
3276 3277
		for_each_rcu_flavor(rsp)
			rcu_cleanup_dead_cpu(cpu, rsp);
3278 3279 3280 3281
		break;
	default:
		break;
	}
3282
	trace_rcu_utilization(TPS("End CPU hotplug"));
3283
	return NOTIFY_OK;
3284 3285
}

3286 3287 3288 3289 3290 3291 3292 3293 3294 3295 3296 3297 3298 3299 3300 3301 3302 3303 3304
static int rcu_pm_notify(struct notifier_block *self,
			 unsigned long action, void *hcpu)
{
	switch (action) {
	case PM_HIBERNATION_PREPARE:
	case PM_SUSPEND_PREPARE:
		if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */
			rcu_expedited = 1;
		break;
	case PM_POST_HIBERNATION:
	case PM_POST_SUSPEND:
		rcu_expedited = 0;
		break;
	default:
		break;
	}
	return NOTIFY_OK;
}

3305 3306 3307 3308 3309 3310 3311 3312 3313 3314 3315
/*
 * Spawn the kthread that handles this RCU flavor's grace periods.
 */
static int __init rcu_spawn_gp_kthread(void)
{
	unsigned long flags;
	struct rcu_node *rnp;
	struct rcu_state *rsp;
	struct task_struct *t;

	for_each_rcu_flavor(rsp) {
3316
		t = kthread_run(rcu_gp_kthread, rsp, "%s", rsp->name);
3317 3318 3319 3320 3321
		BUG_ON(IS_ERR(t));
		rnp = rcu_get_root(rsp);
		raw_spin_lock_irqsave(&rnp->lock, flags);
		rsp->gp_kthread = t;
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
P
Paul E. McKenney 已提交
3322
		rcu_spawn_nocb_kthreads(rsp);
3323 3324 3325 3326 3327
	}
	return 0;
}
early_initcall(rcu_spawn_gp_kthread);

3328 3329 3330 3331 3332 3333 3334 3335 3336 3337 3338 3339 3340 3341 3342
/*
 * 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;
}

3343 3344 3345 3346 3347 3348 3349 3350 3351
/*
 * 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;

3352 3353
	rsp->levelspread[rcu_num_lvls - 1] = rcu_fanout_leaf;
	for (i = rcu_num_lvls - 2; i >= 0; i--)
3354 3355 3356 3357 3358 3359 3360 3361 3362
		rsp->levelspread[i] = CONFIG_RCU_FANOUT;
}
#else /* #ifdef CONFIG_RCU_FANOUT_EXACT */
static void __init rcu_init_levelspread(struct rcu_state *rsp)
{
	int ccur;
	int cprv;
	int i;

3363
	cprv = nr_cpu_ids;
3364
	for (i = rcu_num_lvls - 1; i >= 0; i--) {
3365 3366 3367 3368 3369 3370 3371 3372 3373 3374
		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.
 */
3375 3376
static void __init rcu_init_one(struct rcu_state *rsp,
		struct rcu_data __percpu *rda)
3377
{
3378 3379 3380 3381 3382 3383 3384 3385
	static char *buf[] = { "rcu_node_0",
			       "rcu_node_1",
			       "rcu_node_2",
			       "rcu_node_3" };  /* Match MAX_RCU_LVLS */
	static char *fqs[] = { "rcu_node_fqs_0",
			       "rcu_node_fqs_1",
			       "rcu_node_fqs_2",
			       "rcu_node_fqs_3" };  /* Match MAX_RCU_LVLS */
3386 3387 3388 3389 3390
	int cpustride = 1;
	int i;
	int j;
	struct rcu_node *rnp;

3391 3392
	BUILD_BUG_ON(MAX_RCU_LVLS > ARRAY_SIZE(buf));  /* Fix buf[] init! */

3393 3394 3395 3396
	/* Silence gcc 4.8 warning about array index out of range. */
	if (rcu_num_lvls > RCU_NUM_LVLS)
		panic("rcu_init_one: rcu_num_lvls overflow");

3397 3398
	/* Initialize the level-tracking arrays. */

3399 3400 3401
	for (i = 0; i < rcu_num_lvls; i++)
		rsp->levelcnt[i] = num_rcu_lvl[i];
	for (i = 1; i < rcu_num_lvls; i++)
3402 3403 3404 3405 3406
		rsp->level[i] = rsp->level[i - 1] + rsp->levelcnt[i - 1];
	rcu_init_levelspread(rsp);

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

3407
	for (i = rcu_num_lvls - 1; i >= 0; i--) {
3408 3409 3410
		cpustride *= rsp->levelspread[i];
		rnp = rsp->level[i];
		for (j = 0; j < rsp->levelcnt[i]; j++, rnp++) {
P
Paul E. McKenney 已提交
3411
			raw_spin_lock_init(&rnp->lock);
3412 3413
			lockdep_set_class_and_name(&rnp->lock,
						   &rcu_node_class[i], buf[i]);
3414 3415 3416
			raw_spin_lock_init(&rnp->fqslock);
			lockdep_set_class_and_name(&rnp->fqslock,
						   &rcu_fqs_class[i], fqs[i]);
3417 3418
			rnp->gpnum = rsp->gpnum;
			rnp->completed = rsp->completed;
3419 3420 3421 3422 3423 3424 3425 3426 3427 3428 3429 3430 3431 3432 3433 3434 3435
			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;
3436
			INIT_LIST_HEAD(&rnp->blkd_tasks);
3437
			rcu_init_one_nocb(rnp);
3438 3439
		}
	}
3440

3441
	rsp->rda = rda;
3442
	init_waitqueue_head(&rsp->gp_wq);
3443
	init_irq_work(&rsp->wakeup_work, rsp_wakeup);
3444
	rnp = rsp->level[rcu_num_lvls - 1];
3445
	for_each_possible_cpu(i) {
3446
		while (i > rnp->grphi)
3447
			rnp++;
3448
		per_cpu_ptr(rsp->rda, i)->mynode = rnp;
3449 3450
		rcu_boot_init_percpu_data(i, rsp);
	}
3451
	list_add(&rsp->flavors, &rcu_struct_flavors);
3452 3453
}

3454 3455
/*
 * Compute the rcu_node tree geometry from kernel parameters.  This cannot
3456
 * replace the definitions in tree.h because those are needed to size
3457 3458 3459 3460
 * the ->node array in the rcu_state structure.
 */
static void __init rcu_init_geometry(void)
{
3461
	ulong d;
3462 3463
	int i;
	int j;
3464
	int n = nr_cpu_ids;
3465 3466
	int rcu_capacity[MAX_RCU_LVLS + 1];

3467 3468 3469 3470 3471 3472 3473 3474 3475 3476 3477 3478 3479
	/*
	 * Initialize any unspecified boot parameters.
	 * The default values of jiffies_till_first_fqs and
	 * jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS
	 * value, which is a function of HZ, then adding one for each
	 * RCU_JIFFIES_FQS_DIV CPUs that might be on the system.
	 */
	d = RCU_JIFFIES_TILL_FORCE_QS + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
	if (jiffies_till_first_fqs == ULONG_MAX)
		jiffies_till_first_fqs = d;
	if (jiffies_till_next_fqs == ULONG_MAX)
		jiffies_till_next_fqs = d;

3480
	/* If the compile-time values are accurate, just leave. */
3481 3482
	if (rcu_fanout_leaf == CONFIG_RCU_FANOUT_LEAF &&
	    nr_cpu_ids == NR_CPUS)
3483
		return;
3484 3485
	pr_info("RCU: Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%d\n",
		rcu_fanout_leaf, nr_cpu_ids);
3486 3487 3488 3489 3490 3491 3492 3493 3494 3495 3496 3497 3498 3499 3500 3501 3502 3503 3504 3505 3506 3507 3508 3509 3510 3511 3512 3513 3514 3515 3516 3517 3518 3519 3520 3521 3522 3523 3524 3525 3526 3527 3528 3529 3530

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

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

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

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

3531
void __init rcu_init(void)
3532
{
P
Paul E. McKenney 已提交
3533
	int cpu;
3534

3535
	rcu_bootup_announce();
3536
	rcu_init_geometry();
3537
	rcu_init_one(&rcu_bh_state, &rcu_bh_data);
3538
	rcu_init_one(&rcu_sched_state, &rcu_sched_data);
3539
	__rcu_init_preempt();
J
Jiang Fang 已提交
3540
	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
3541 3542 3543 3544 3545 3546 3547

	/*
	 * 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);
3548
	pm_notifier(rcu_pm_notify, 0);
P
Paul E. McKenney 已提交
3549 3550
	for_each_online_cpu(cpu)
		rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
3551 3552
}

3553
#include "tree_plugin.h"