srcutree.c 39.4 KB
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/*
 * Sleepable Read-Copy Update mechanism for mutual exclusion.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, you can access it online at
 * http://www.gnu.org/licenses/gpl-2.0.html.
 *
 * Copyright (C) IBM Corporation, 2006
 * Copyright (C) Fujitsu, 2012
 *
 * Author: Paul McKenney <paulmck@us.ibm.com>
 *	   Lai Jiangshan <laijs@cn.fujitsu.com>
 *
 * For detailed explanation of Read-Copy Update mechanism see -
 *		Documentation/RCU/ *.txt
 *
 */

#include <linux/export.h>
#include <linux/mutex.h>
#include <linux/percpu.h>
#include <linux/preempt.h>
#include <linux/rcupdate_wait.h>
#include <linux/sched.h>
#include <linux/smp.h>
#include <linux/delay.h>
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#include <linux/module.h>
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#include <linux/srcu.h>

#include "rcu.h"
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#include "rcu_segcblist.h"
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/* Holdoff in nanoseconds for auto-expediting. */
#define DEFAULT_SRCU_EXP_HOLDOFF (25 * 1000)
static ulong exp_holdoff = DEFAULT_SRCU_EXP_HOLDOFF;
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module_param(exp_holdoff, ulong, 0444);

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static void srcu_invoke_callbacks(struct work_struct *work);
static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay);

/*
 * Initialize SRCU combining tree.  Note that statically allocated
 * srcu_struct structures might already have srcu_read_lock() and
 * srcu_read_unlock() running against them.  So if the is_static parameter
 * is set, don't initialize ->srcu_lock_count[] and ->srcu_unlock_count[].
 */
static void init_srcu_struct_nodes(struct srcu_struct *sp, bool is_static)
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{
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	int cpu;
	int i;
	int level = 0;
	int levelspread[RCU_NUM_LVLS];
	struct srcu_data *sdp;
	struct srcu_node *snp;
	struct srcu_node *snp_first;

	/* Work out the overall tree geometry. */
	sp->level[0] = &sp->node[0];
	for (i = 1; i < rcu_num_lvls; i++)
		sp->level[i] = sp->level[i - 1] + num_rcu_lvl[i - 1];
	rcu_init_levelspread(levelspread, num_rcu_lvl);

	/* Each pass through this loop initializes one srcu_node structure. */
	rcu_for_each_node_breadth_first(sp, snp) {
		spin_lock_init(&snp->lock);
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		WARN_ON_ONCE(ARRAY_SIZE(snp->srcu_have_cbs) !=
			     ARRAY_SIZE(snp->srcu_data_have_cbs));
		for (i = 0; i < ARRAY_SIZE(snp->srcu_have_cbs); i++) {
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			snp->srcu_have_cbs[i] = 0;
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			snp->srcu_data_have_cbs[i] = 0;
		}
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		snp->srcu_gp_seq_needed_exp = 0;
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		snp->grplo = -1;
		snp->grphi = -1;
		if (snp == &sp->node[0]) {
			/* Root node, special case. */
			snp->srcu_parent = NULL;
			continue;
		}

		/* Non-root node. */
		if (snp == sp->level[level + 1])
			level++;
		snp->srcu_parent = sp->level[level - 1] +
				   (snp - sp->level[level]) /
				   levelspread[level - 1];
	}

	/*
	 * Initialize the per-CPU srcu_data array, which feeds into the
	 * leaves of the srcu_node tree.
	 */
	WARN_ON_ONCE(ARRAY_SIZE(sdp->srcu_lock_count) !=
		     ARRAY_SIZE(sdp->srcu_unlock_count));
	level = rcu_num_lvls - 1;
	snp_first = sp->level[level];
	for_each_possible_cpu(cpu) {
		sdp = per_cpu_ptr(sp->sda, cpu);
		spin_lock_init(&sdp->lock);
		rcu_segcblist_init(&sdp->srcu_cblist);
		sdp->srcu_cblist_invoking = false;
		sdp->srcu_gp_seq_needed = sp->srcu_gp_seq;
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		sdp->srcu_gp_seq_needed_exp = sp->srcu_gp_seq;
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		sdp->mynode = &snp_first[cpu / levelspread[level]];
		for (snp = sdp->mynode; snp != NULL; snp = snp->srcu_parent) {
			if (snp->grplo < 0)
				snp->grplo = cpu;
			snp->grphi = cpu;
		}
		sdp->cpu = cpu;
		INIT_DELAYED_WORK(&sdp->work, srcu_invoke_callbacks);
		sdp->sp = sp;
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		sdp->grpmask = 1 << (cpu - sdp->mynode->grplo);
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		if (is_static)
			continue;

		/* Dynamically allocated, better be no srcu_read_locks()! */
		for (i = 0; i < ARRAY_SIZE(sdp->srcu_lock_count); i++) {
			sdp->srcu_lock_count[i] = 0;
			sdp->srcu_unlock_count[i] = 0;
		}
	}
}

/*
 * Initialize non-compile-time initialized fields, including the
 * associated srcu_node and srcu_data structures.  The is_static
 * parameter is passed through to init_srcu_struct_nodes(), and
 * also tells us that ->sda has already been wired up to srcu_data.
 */
static int init_srcu_struct_fields(struct srcu_struct *sp, bool is_static)
{
	mutex_init(&sp->srcu_cb_mutex);
	mutex_init(&sp->srcu_gp_mutex);
	sp->srcu_idx = 0;
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	sp->srcu_gp_seq = 0;
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	sp->srcu_barrier_seq = 0;
	mutex_init(&sp->srcu_barrier_mutex);
	atomic_set(&sp->srcu_barrier_cpu_cnt, 0);
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	INIT_DELAYED_WORK(&sp->work, process_srcu);
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	if (!is_static)
		sp->sda = alloc_percpu(struct srcu_data);
	init_srcu_struct_nodes(sp, is_static);
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	sp->srcu_gp_seq_needed_exp = 0;
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	sp->srcu_last_gp_end = ktime_get_mono_fast_ns();
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	smp_store_release(&sp->srcu_gp_seq_needed, 0); /* Init done. */
	return sp->sda ? 0 : -ENOMEM;
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}

#ifdef CONFIG_DEBUG_LOCK_ALLOC

int __init_srcu_struct(struct srcu_struct *sp, const char *name,
		       struct lock_class_key *key)
{
	/* Don't re-initialize a lock while it is held. */
	debug_check_no_locks_freed((void *)sp, sizeof(*sp));
	lockdep_init_map(&sp->dep_map, name, key, 0);
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	spin_lock_init(&sp->gp_lock);
	return init_srcu_struct_fields(sp, false);
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}
EXPORT_SYMBOL_GPL(__init_srcu_struct);

#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */

/**
 * init_srcu_struct - initialize a sleep-RCU structure
 * @sp: structure to initialize.
 *
 * Must invoke this on a given srcu_struct before passing that srcu_struct
 * to any other function.  Each srcu_struct represents a separate domain
 * of SRCU protection.
 */
int init_srcu_struct(struct srcu_struct *sp)
{
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	spin_lock_init(&sp->gp_lock);
	return init_srcu_struct_fields(sp, false);
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}
EXPORT_SYMBOL_GPL(init_srcu_struct);

#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */

/*
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 * First-use initialization of statically allocated srcu_struct
 * structure.  Wiring up the combining tree is more than can be
 * done with compile-time initialization, so this check is added
 * to each update-side SRCU primitive.  Use ->gp_lock, which -is-
 * compile-time initialized, to resolve races involving multiple
 * CPUs trying to garner first-use privileges.
 */
static void check_init_srcu_struct(struct srcu_struct *sp)
{
	unsigned long flags;

	WARN_ON_ONCE(rcu_scheduler_active == RCU_SCHEDULER_INIT);
	/* The smp_load_acquire() pairs with the smp_store_release(). */
	if (!rcu_seq_state(smp_load_acquire(&sp->srcu_gp_seq_needed))) /*^^^*/
		return; /* Already initialized. */
	spin_lock_irqsave(&sp->gp_lock, flags);
	if (!rcu_seq_state(sp->srcu_gp_seq_needed)) {
		spin_unlock_irqrestore(&sp->gp_lock, flags);
		return;
	}
	init_srcu_struct_fields(sp, true);
	spin_unlock_irqrestore(&sp->gp_lock, flags);
}

/*
 * Returns approximate total of the readers' ->srcu_lock_count[] values
 * for the rank of per-CPU counters specified by idx.
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 */
static unsigned long srcu_readers_lock_idx(struct srcu_struct *sp, int idx)
{
	int cpu;
	unsigned long sum = 0;

	for_each_possible_cpu(cpu) {
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		struct srcu_data *cpuc = per_cpu_ptr(sp->sda, cpu);
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		sum += READ_ONCE(cpuc->srcu_lock_count[idx]);
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	}
	return sum;
}

/*
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 * Returns approximate total of the readers' ->srcu_unlock_count[] values
 * for the rank of per-CPU counters specified by idx.
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 */
static unsigned long srcu_readers_unlock_idx(struct srcu_struct *sp, int idx)
{
	int cpu;
	unsigned long sum = 0;

	for_each_possible_cpu(cpu) {
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		struct srcu_data *cpuc = per_cpu_ptr(sp->sda, cpu);
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		sum += READ_ONCE(cpuc->srcu_unlock_count[idx]);
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	}
	return sum;
}

/*
 * Return true if the number of pre-existing readers is determined to
 * be zero.
 */
static bool srcu_readers_active_idx_check(struct srcu_struct *sp, int idx)
{
	unsigned long unlocks;

	unlocks = srcu_readers_unlock_idx(sp, idx);

	/*
	 * Make sure that a lock is always counted if the corresponding
	 * unlock is counted. Needs to be a smp_mb() as the read side may
	 * contain a read from a variable that is written to before the
	 * synchronize_srcu() in the write side. In this case smp_mb()s
	 * A and B act like the store buffering pattern.
	 *
	 * This smp_mb() also pairs with smp_mb() C to prevent accesses
	 * after the synchronize_srcu() from being executed before the
	 * grace period ends.
	 */
	smp_mb(); /* A */

	/*
	 * If the locks are the same as the unlocks, then there must have
	 * been no readers on this index at some time in between. This does
	 * not mean that there are no more readers, as one could have read
	 * the current index but not have incremented the lock counter yet.
	 *
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	 * So suppose that the updater is preempted here for so long
	 * that more than ULONG_MAX non-nested readers come and go in
	 * the meantime.  It turns out that this cannot result in overflow
	 * because if a reader modifies its unlock count after we read it
	 * above, then that reader's next load of ->srcu_idx is guaranteed
	 * to get the new value, which will cause it to operate on the
	 * other bank of counters, where it cannot contribute to the
	 * overflow of these counters.  This means that there is a maximum
	 * of 2*NR_CPUS increments, which cannot overflow given current
	 * systems, especially not on 64-bit systems.
	 *
	 * OK, how about nesting?  This does impose a limit on nesting
	 * of floor(ULONG_MAX/NR_CPUS/2), which should be sufficient,
	 * especially on 64-bit systems.
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	 */
	return srcu_readers_lock_idx(sp, idx) == unlocks;
}

/**
 * srcu_readers_active - returns true if there are readers. and false
 *                       otherwise
 * @sp: which srcu_struct to count active readers (holding srcu_read_lock).
 *
 * Note that this is not an atomic primitive, and can therefore suffer
 * severe errors when invoked on an active srcu_struct.  That said, it
 * can be useful as an error check at cleanup time.
 */
static bool srcu_readers_active(struct srcu_struct *sp)
{
	int cpu;
	unsigned long sum = 0;

	for_each_possible_cpu(cpu) {
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		struct srcu_data *cpuc = per_cpu_ptr(sp->sda, cpu);
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		sum += READ_ONCE(cpuc->srcu_lock_count[0]);
		sum += READ_ONCE(cpuc->srcu_lock_count[1]);
		sum -= READ_ONCE(cpuc->srcu_unlock_count[0]);
		sum -= READ_ONCE(cpuc->srcu_unlock_count[1]);
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	}
	return sum;
}

#define SRCU_INTERVAL		1

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/*
 * Return grace-period delay, zero if there are expedited grace
 * periods pending, SRCU_INTERVAL otherwise.
 */
static unsigned long srcu_get_delay(struct srcu_struct *sp)
{
	if (ULONG_CMP_LT(READ_ONCE(sp->srcu_gp_seq),
			 READ_ONCE(sp->srcu_gp_seq_needed_exp)))
		return 0;
	return SRCU_INTERVAL;
}

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/**
 * cleanup_srcu_struct - deconstruct a sleep-RCU structure
 * @sp: structure to clean up.
 *
 * Must invoke this after you are finished using a given srcu_struct that
 * was initialized via init_srcu_struct(), else you leak memory.
 */
void cleanup_srcu_struct(struct srcu_struct *sp)
{
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	int cpu;

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	if (WARN_ON(!srcu_get_delay(sp)))
		return; /* Leakage unless caller handles error. */
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	if (WARN_ON(srcu_readers_active(sp)))
		return; /* Leakage unless caller handles error. */
	flush_delayed_work(&sp->work);
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	for_each_possible_cpu(cpu)
		flush_delayed_work(&per_cpu_ptr(sp->sda, cpu)->work);
	if (WARN_ON(rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) != SRCU_STATE_IDLE) ||
	    WARN_ON(srcu_readers_active(sp))) {
		pr_info("cleanup_srcu_struct: Active srcu_struct %p state: %d\n", sp, rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)));
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		return; /* Caller forgot to stop doing call_srcu()? */
	}
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	free_percpu(sp->sda);
	sp->sda = NULL;
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}
EXPORT_SYMBOL_GPL(cleanup_srcu_struct);

/*
 * Counts the new reader in the appropriate per-CPU element of the
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 * srcu_struct.
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 * Returns an index that must be passed to the matching srcu_read_unlock().
 */
int __srcu_read_lock(struct srcu_struct *sp)
{
	int idx;

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	idx = READ_ONCE(sp->srcu_idx) & 0x1;
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	this_cpu_inc(sp->sda->srcu_lock_count[idx]);
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	smp_mb(); /* B */  /* Avoid leaking the critical section. */
	return idx;
}
EXPORT_SYMBOL_GPL(__srcu_read_lock);

/*
 * Removes the count for the old reader from the appropriate per-CPU
 * element of the srcu_struct.  Note that this may well be a different
 * CPU than that which was incremented by the corresponding srcu_read_lock().
 */
void __srcu_read_unlock(struct srcu_struct *sp, int idx)
{
	smp_mb(); /* C */  /* Avoid leaking the critical section. */
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	this_cpu_inc(sp->sda->srcu_unlock_count[idx]);
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}
EXPORT_SYMBOL_GPL(__srcu_read_unlock);

/*
 * We use an adaptive strategy for synchronize_srcu() and especially for
 * synchronize_srcu_expedited().  We spin for a fixed time period
 * (defined below) to allow SRCU readers to exit their read-side critical
 * sections.  If there are still some readers after a few microseconds,
 * we repeatedly block for 1-millisecond time periods.
 */
#define SRCU_RETRY_CHECK_DELAY		5

/*
 * Start an SRCU grace period.
 */
static void srcu_gp_start(struct srcu_struct *sp)
{
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	struct srcu_data *sdp = this_cpu_ptr(sp->sda);
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	int state;

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	RCU_LOCKDEP_WARN(!lockdep_is_held(&sp->gp_lock),
			 "Invoked srcu_gp_start() without ->gp_lock!");
	WARN_ON_ONCE(ULONG_CMP_GE(sp->srcu_gp_seq, sp->srcu_gp_seq_needed));
	rcu_segcblist_advance(&sdp->srcu_cblist,
			      rcu_seq_current(&sp->srcu_gp_seq));
	(void)rcu_segcblist_accelerate(&sdp->srcu_cblist,
				       rcu_seq_snap(&sp->srcu_gp_seq));
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	smp_mb(); /* Order prior store to ->srcu_gp_seq_needed vs. GP start. */
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	rcu_seq_start(&sp->srcu_gp_seq);
	state = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
	WARN_ON_ONCE(state != SRCU_STATE_SCAN1);
}

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/*
 * Track online CPUs to guide callback workqueue placement.
 */
DEFINE_PER_CPU(bool, srcu_online);

void srcu_online_cpu(unsigned int cpu)
{
	WRITE_ONCE(per_cpu(srcu_online, cpu), true);
}

void srcu_offline_cpu(unsigned int cpu)
{
	WRITE_ONCE(per_cpu(srcu_online, cpu), false);
}

/*
 * Place the workqueue handler on the specified CPU if online, otherwise
 * just run it whereever.  This is useful for placing workqueue handlers
 * that are to invoke the specified CPU's callbacks.
 */
static bool srcu_queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
				       struct delayed_work *dwork,
				       unsigned long delay)
{
	bool ret;

	preempt_disable();
	if (READ_ONCE(per_cpu(srcu_online, cpu)))
		ret = queue_delayed_work_on(cpu, wq, dwork, delay);
	else
		ret = queue_delayed_work(wq, dwork, delay);
	preempt_enable();
	return ret;
}

/*
 * Schedule callback invocation for the specified srcu_data structure,
 * if possible, on the corresponding CPU.
 */
static void srcu_schedule_cbs_sdp(struct srcu_data *sdp, unsigned long delay)
{
	srcu_queue_delayed_work_on(sdp->cpu, system_power_efficient_wq,
				   &sdp->work, delay);
}

/*
 * Schedule callback invocation for all srcu_data structures associated
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 * with the specified srcu_node structure that have callbacks for the
 * just-completed grace period, the one corresponding to idx.  If possible,
 * schedule this invocation on the corresponding CPUs.
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 */
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static void srcu_schedule_cbs_snp(struct srcu_struct *sp, struct srcu_node *snp,
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				  unsigned long mask, unsigned long delay)
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{
	int cpu;

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	for (cpu = snp->grplo; cpu <= snp->grphi; cpu++) {
		if (!(mask & (1 << (cpu - snp->grplo))))
			continue;
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		srcu_schedule_cbs_sdp(per_cpu_ptr(sp->sda, cpu), delay);
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	}
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}

/*
 * Note the end of an SRCU grace period.  Initiates callback invocation
 * and starts a new grace period if needed.
 *
 * The ->srcu_cb_mutex acquisition does not protect any data, but
 * instead prevents more than one grace period from starting while we
 * are initiating callback invocation.  This allows the ->srcu_have_cbs[]
 * array to have a finite number of elements.
 */
static void srcu_gp_end(struct srcu_struct *sp)
{
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	unsigned long cbdelay;
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	bool cbs;
	unsigned long gpseq;
	int idx;
	int idxnext;
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	unsigned long mask;
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	struct srcu_node *snp;

	/* Prevent more than one additional grace period. */
	mutex_lock(&sp->srcu_cb_mutex);

	/* End the current grace period. */
	spin_lock_irq(&sp->gp_lock);
	idx = rcu_seq_state(sp->srcu_gp_seq);
	WARN_ON_ONCE(idx != SRCU_STATE_SCAN2);
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	cbdelay = srcu_get_delay(sp);
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	sp->srcu_last_gp_end = ktime_get_mono_fast_ns();
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	rcu_seq_end(&sp->srcu_gp_seq);
	gpseq = rcu_seq_current(&sp->srcu_gp_seq);
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	if (ULONG_CMP_LT(sp->srcu_gp_seq_needed_exp, gpseq))
		sp->srcu_gp_seq_needed_exp = gpseq;
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	spin_unlock_irq(&sp->gp_lock);
	mutex_unlock(&sp->srcu_gp_mutex);
	/* A new grace period can start at this point.  But only one. */

	/* Initiate callback invocation as needed. */
	idx = rcu_seq_ctr(gpseq) % ARRAY_SIZE(snp->srcu_have_cbs);
	idxnext = (idx + 1) % ARRAY_SIZE(snp->srcu_have_cbs);
	rcu_for_each_node_breadth_first(sp, snp) {
		spin_lock_irq(&snp->lock);
		cbs = false;
		if (snp >= sp->level[rcu_num_lvls - 1])
			cbs = snp->srcu_have_cbs[idx] == gpseq;
		snp->srcu_have_cbs[idx] = gpseq;
		rcu_seq_set_state(&snp->srcu_have_cbs[idx], 1);
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		if (ULONG_CMP_LT(snp->srcu_gp_seq_needed_exp, gpseq))
			snp->srcu_gp_seq_needed_exp = gpseq;
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		mask = snp->srcu_data_have_cbs[idx];
		snp->srcu_data_have_cbs[idx] = 0;
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		spin_unlock_irq(&snp->lock);
		if (cbs) {
			smp_mb(); /* GP end before CB invocation. */
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			srcu_schedule_cbs_snp(sp, snp, mask, cbdelay);
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		}
	}

	/* Callback initiation done, allow grace periods after next. */
	mutex_unlock(&sp->srcu_cb_mutex);

	/* Start a new grace period if needed. */
	spin_lock_irq(&sp->gp_lock);
	gpseq = rcu_seq_current(&sp->srcu_gp_seq);
	if (!rcu_seq_state(gpseq) &&
	    ULONG_CMP_LT(gpseq, sp->srcu_gp_seq_needed)) {
		srcu_gp_start(sp);
		spin_unlock_irq(&sp->gp_lock);
		/* Throttle expedited grace periods: Should be rare! */
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		srcu_reschedule(sp, rcu_seq_ctr(gpseq) & 0x3ff
				    ? 0 : SRCU_INTERVAL);
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	} else {
		spin_unlock_irq(&sp->gp_lock);
	}
}

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/*
 * Funnel-locking scheme to scalably mediate many concurrent expedited
 * grace-period requests.  This function is invoked for the first known
 * expedited request for a grace period that has already been requested,
 * but without expediting.  To start a completely new grace period,
 * whether expedited or not, use srcu_funnel_gp_start() instead.
 */
static void srcu_funnel_exp_start(struct srcu_struct *sp, struct srcu_node *snp,
				  unsigned long s)
{
	unsigned long flags;

	for (; snp != NULL; snp = snp->srcu_parent) {
		if (rcu_seq_done(&sp->srcu_gp_seq, s) ||
		    ULONG_CMP_GE(READ_ONCE(snp->srcu_gp_seq_needed_exp), s))
			return;
		spin_lock_irqsave(&snp->lock, flags);
		if (ULONG_CMP_GE(snp->srcu_gp_seq_needed_exp, s)) {
			spin_unlock_irqrestore(&snp->lock, flags);
			return;
		}
		WRITE_ONCE(snp->srcu_gp_seq_needed_exp, s);
		spin_unlock_irqrestore(&snp->lock, flags);
	}
	spin_lock_irqsave(&sp->gp_lock, flags);
	if (!ULONG_CMP_LT(sp->srcu_gp_seq_needed_exp, s))
		sp->srcu_gp_seq_needed_exp = s;
	spin_unlock_irqrestore(&sp->gp_lock, flags);
}

591 592 593 594 595 596 597
/*
 * Funnel-locking scheme to scalably mediate many concurrent grace-period
 * requests.  The winner has to do the work of actually starting grace
 * period s.  Losers must either ensure that their desired grace-period
 * number is recorded on at least their leaf srcu_node structure, or they
 * must take steps to invoke their own callbacks.
 */
598 599
static void srcu_funnel_gp_start(struct srcu_struct *sp, struct srcu_data *sdp,
				 unsigned long s, bool do_norm)
600 601 602 603 604 605 606 607 608 609 610 611 612
{
	unsigned long flags;
	int idx = rcu_seq_ctr(s) % ARRAY_SIZE(sdp->mynode->srcu_have_cbs);
	struct srcu_node *snp = sdp->mynode;
	unsigned long snp_seq;

	/* Each pass through the loop does one level of the srcu_node tree. */
	for (; snp != NULL; snp = snp->srcu_parent) {
		if (rcu_seq_done(&sp->srcu_gp_seq, s) && snp != sdp->mynode)
			return; /* GP already done and CBs recorded. */
		spin_lock_irqsave(&snp->lock, flags);
		if (ULONG_CMP_GE(snp->srcu_have_cbs[idx], s)) {
			snp_seq = snp->srcu_have_cbs[idx];
613 614
			if (snp == sdp->mynode && snp_seq == s)
				snp->srcu_data_have_cbs[idx] |= sdp->grpmask;
615 616 617
			spin_unlock_irqrestore(&snp->lock, flags);
			if (snp == sdp->mynode && snp_seq != s) {
				smp_mb(); /* CBs after GP! */
618 619 620 621
				srcu_schedule_cbs_sdp(sdp, do_norm
							   ? SRCU_INTERVAL
							   : 0);
				return;
622
			}
623 624
			if (!do_norm)
				srcu_funnel_exp_start(sp, snp, s);
625 626 627
			return;
		}
		snp->srcu_have_cbs[idx] = s;
628 629
		if (snp == sdp->mynode)
			snp->srcu_data_have_cbs[idx] |= sdp->grpmask;
630 631
		if (!do_norm && ULONG_CMP_LT(snp->srcu_gp_seq_needed_exp, s))
			snp->srcu_gp_seq_needed_exp = s;
632 633 634 635 636 637 638 639 640 641 642 643
		spin_unlock_irqrestore(&snp->lock, flags);
	}

	/* Top of tree, must ensure the grace period will be started. */
	spin_lock_irqsave(&sp->gp_lock, flags);
	if (ULONG_CMP_LT(sp->srcu_gp_seq_needed, s)) {
		/*
		 * Record need for grace period s.  Pair with load
		 * acquire setting up for initialization.
		 */
		smp_store_release(&sp->srcu_gp_seq_needed, s); /*^^^*/
	}
644 645
	if (!do_norm && ULONG_CMP_LT(sp->srcu_gp_seq_needed_exp, s))
		sp->srcu_gp_seq_needed_exp = s;
646 647 648 649 650 651 652

	/* If grace period not already done and none in progress, start it. */
	if (!rcu_seq_done(&sp->srcu_gp_seq, s) &&
	    rcu_seq_state(sp->srcu_gp_seq) == SRCU_STATE_IDLE) {
		WARN_ON_ONCE(ULONG_CMP_GE(sp->srcu_gp_seq, sp->srcu_gp_seq_needed));
		srcu_gp_start(sp);
		queue_delayed_work(system_power_efficient_wq, &sp->work,
653
				   srcu_get_delay(sp));
654 655 656 657
	}
	spin_unlock_irqrestore(&sp->gp_lock, flags);
}

658 659 660
/*
 * Wait until all readers counted by array index idx complete, but
 * loop an additional time if there is an expedited grace period pending.
661
 * The caller must ensure that ->srcu_idx is not changed while checking.
662 663 664 665 666 667
 */
static bool try_check_zero(struct srcu_struct *sp, int idx, int trycount)
{
	for (;;) {
		if (srcu_readers_active_idx_check(sp, idx))
			return true;
668
		if (--trycount + !srcu_get_delay(sp) <= 0)
669 670 671 672 673 674
			return false;
		udelay(SRCU_RETRY_CHECK_DELAY);
	}
}

/*
675 676
 * Increment the ->srcu_idx counter so that future SRCU readers will
 * use the other rank of the ->srcu_(un)lock_count[] arrays.  This allows
677 678 679 680
 * us to wait for pre-existing readers in a starvation-free manner.
 */
static void srcu_flip(struct srcu_struct *sp)
{
681 682 683 684 685 686 687 688 689 690
	/*
	 * Ensure that if this updater saw a given reader's increment
	 * from __srcu_read_lock(), that reader was using an old value
	 * of ->srcu_idx.  Also ensure that if a given reader sees the
	 * new value of ->srcu_idx, this updater's earlier scans cannot
	 * have seen that reader's increments (which is OK, because this
	 * grace period need not wait on that reader).
	 */
	smp_mb(); /* E */  /* Pairs with B and C. */

691
	WRITE_ONCE(sp->srcu_idx, sp->srcu_idx + 1);
692 693 694 695 696 697 698 699 700 701 702

	/*
	 * Ensure that if the updater misses an __srcu_read_unlock()
	 * increment, that task's next __srcu_read_lock() will see the
	 * above counter update.  Note that both this memory barrier
	 * and the one in srcu_readers_active_idx_check() provide the
	 * guarantee for __srcu_read_lock().
	 */
	smp_mb(); /* D */  /* Pairs with C. */
}

703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725
/*
 * If SRCU is likely idle, return true, otherwise return false.
 *
 * Note that it is OK for several current from-idle requests for a new
 * grace period from idle to specify expediting because they will all end
 * up requesting the same grace period anyhow.  So no loss.
 *
 * Note also that if any CPU (including the current one) is still invoking
 * callbacks, this function will nevertheless say "idle".  This is not
 * ideal, but the overhead of checking all CPUs' callback lists is even
 * less ideal, especially on large systems.  Furthermore, the wakeup
 * can happen before the callback is fully removed, so we have no choice
 * but to accept this type of error.
 *
 * This function is also subject to counter-wrap errors, but let's face
 * it, if this function was preempted for enough time for the counters
 * to wrap, it really doesn't matter whether or not we expedite the grace
 * period.  The extra overhead of a needlessly expedited grace period is
 * negligible when amoritized over that time period, and the extra latency
 * of a needlessly non-expedited grace period is similarly negligible.
 */
static bool srcu_might_be_idle(struct srcu_struct *sp)
{
726
	unsigned long curseq;
727 728
	unsigned long flags;
	struct srcu_data *sdp;
729
	unsigned long t;
730 731 732 733 734 735 736 737 738 739 740 741 742 743 744

	/* If the local srcu_data structure has callbacks, not idle.  */
	local_irq_save(flags);
	sdp = this_cpu_ptr(sp->sda);
	if (rcu_segcblist_pend_cbs(&sdp->srcu_cblist)) {
		local_irq_restore(flags);
		return false; /* Callbacks already present, so not idle. */
	}
	local_irq_restore(flags);

	/*
	 * No local callbacks, so probabalistically probe global state.
	 * Exact information would require acquiring locks, which would
	 * kill scalability, hence the probabalistic nature of the probe.
	 */
745 746 747 748 749 750 751 752 753

	/* First, see if enough time has passed since the last GP. */
	t = ktime_get_mono_fast_ns();
	if (exp_holdoff == 0 ||
	    time_in_range_open(t, sp->srcu_last_gp_end,
			       sp->srcu_last_gp_end + exp_holdoff))
		return false; /* Too soon after last GP. */

	/* Next, check for probable idleness. */
754 755 756 757 758 759 760 761 762 763
	curseq = rcu_seq_current(&sp->srcu_gp_seq);
	smp_mb(); /* Order ->srcu_gp_seq with ->srcu_gp_seq_needed. */
	if (ULONG_CMP_LT(curseq, READ_ONCE(sp->srcu_gp_seq_needed)))
		return false; /* Grace period in progress, so not idle. */
	smp_mb(); /* Order ->srcu_gp_seq with prior access. */
	if (curseq != rcu_seq_current(&sp->srcu_gp_seq))
		return false; /* GP # changed, so not idle. */
	return true; /* With reasonable probability, idle! */
}

764 765 766 767 768 769 770
/*
 * SRCU callback function to leak a callback.
 */
static void srcu_leak_callback(struct rcu_head *rhp)
{
}

771
/*
772 773 774
 * Enqueue an SRCU callback on the srcu_data structure associated with
 * the current CPU and the specified srcu_struct structure, initiating
 * grace-period processing if it is not already running.
775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798
 *
 * Note that all CPUs must agree that the grace period extended beyond
 * all pre-existing SRCU read-side critical section.  On systems with
 * more than one CPU, this means that when "func()" is invoked, each CPU
 * is guaranteed to have executed a full memory barrier since the end of
 * its last corresponding SRCU read-side critical section whose beginning
 * preceded the call to call_rcu().  It also means that each CPU executing
 * an SRCU read-side critical section that continues beyond the start of
 * "func()" must have executed a memory barrier after the call_rcu()
 * but before the beginning of that SRCU 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 call_rcu() and CPU B invoked the
 * resulting SRCU callback function "func()", then both CPU A and CPU
 * B are guaranteed to execute a full memory barrier during the time
 * interval between the call to call_rcu() and the invocation of "func()".
 * This guarantee applies even if CPU A and CPU B are the same CPU (but
 * again only if the system has more than one CPU).
 *
 * Of course, these guarantees apply only for invocations of call_srcu(),
 * srcu_read_lock(), and srcu_read_unlock() that are all passed the same
 * srcu_struct structure.
 */
799 800
void __call_srcu(struct srcu_struct *sp, struct rcu_head *rhp,
		 rcu_callback_t func, bool do_norm)
801 802
{
	unsigned long flags;
803
	bool needexp = false;
804 805 806 807 808
	bool needgp = false;
	unsigned long s;
	struct srcu_data *sdp;

	check_init_srcu_struct(sp);
809 810 811 812 813 814
	if (debug_rcu_head_queue(rhp)) {
		/* Probable double call_srcu(), so leak the callback. */
		WRITE_ONCE(rhp->func, srcu_leak_callback);
		WARN_ONCE(1, "call_srcu(): Leaked duplicate callback\n");
		return;
	}
815 816 817 818 819 820 821 822 823 824 825 826
	rhp->func = func;
	local_irq_save(flags);
	sdp = this_cpu_ptr(sp->sda);
	spin_lock(&sdp->lock);
	rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp, false);
	rcu_segcblist_advance(&sdp->srcu_cblist,
			      rcu_seq_current(&sp->srcu_gp_seq));
	s = rcu_seq_snap(&sp->srcu_gp_seq);
	(void)rcu_segcblist_accelerate(&sdp->srcu_cblist, s);
	if (ULONG_CMP_LT(sdp->srcu_gp_seq_needed, s)) {
		sdp->srcu_gp_seq_needed = s;
		needgp = true;
827
	}
828 829 830 831
	if (!do_norm && ULONG_CMP_LT(sdp->srcu_gp_seq_needed_exp, s)) {
		sdp->srcu_gp_seq_needed_exp = s;
		needexp = true;
	}
832 833
	spin_unlock_irqrestore(&sdp->lock, flags);
	if (needgp)
834 835 836 837 838 839 840 841 842
		srcu_funnel_gp_start(sp, sdp, s, do_norm);
	else if (needexp)
		srcu_funnel_exp_start(sp, sdp->mynode, s);
}

void call_srcu(struct srcu_struct *sp, struct rcu_head *rhp,
	       rcu_callback_t func)
{
	__call_srcu(sp, rhp, func, true);
843 844 845 846 847 848
}
EXPORT_SYMBOL_GPL(call_srcu);

/*
 * Helper function for synchronize_srcu() and synchronize_srcu_expedited().
 */
849
static void __synchronize_srcu(struct srcu_struct *sp, bool do_norm)
850 851 852 853 854 855 856 857 858 859 860 861
{
	struct rcu_synchronize rcu;

	RCU_LOCKDEP_WARN(lock_is_held(&sp->dep_map) ||
			 lock_is_held(&rcu_bh_lock_map) ||
			 lock_is_held(&rcu_lock_map) ||
			 lock_is_held(&rcu_sched_lock_map),
			 "Illegal synchronize_srcu() in same-type SRCU (or in RCU) read-side critical section");

	if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
		return;
	might_sleep();
862
	check_init_srcu_struct(sp);
863
	init_completion(&rcu.completion);
864
	init_rcu_head_on_stack(&rcu.head);
865
	__call_srcu(sp, &rcu.head, wakeme_after_rcu, do_norm);
866
	wait_for_completion(&rcu.completion);
867
	destroy_rcu_head_on_stack(&rcu.head);
868 869 870 871 872 873 874 875 876 877 878 879 880 881
}

/**
 * synchronize_srcu_expedited - Brute-force SRCU grace period
 * @sp: srcu_struct with which to synchronize.
 *
 * Wait for an SRCU grace period to elapse, but be more aggressive about
 * spinning rather than blocking when waiting.
 *
 * Note that synchronize_srcu_expedited() has the same deadlock and
 * memory-ordering properties as does synchronize_srcu().
 */
void synchronize_srcu_expedited(struct srcu_struct *sp)
{
882
	__synchronize_srcu(sp, rcu_gp_is_normal());
883 884 885 886 887 888 889 890 891
}
EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);

/**
 * synchronize_srcu - wait for prior SRCU read-side critical-section completion
 * @sp: srcu_struct with which to synchronize.
 *
 * Wait for the count to drain to zero of both indexes. To avoid the
 * possible starvation of synchronize_srcu(), it waits for the count of
892 893
 * the index=((->srcu_idx & 1) ^ 1) to drain to zero at first,
 * and then flip the srcu_idx and wait for the count of the other index.
894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923
 *
 * Can block; must be called from process context.
 *
 * Note that it is illegal to call synchronize_srcu() from the corresponding
 * SRCU read-side critical section; doing so will result in deadlock.
 * However, it is perfectly legal to call synchronize_srcu() on one
 * srcu_struct from some other srcu_struct's read-side critical section,
 * as long as the resulting graph of srcu_structs is acyclic.
 *
 * There are memory-ordering constraints implied by synchronize_srcu().
 * On systems with more than one CPU, when synchronize_srcu() returns,
 * each CPU is guaranteed to have executed a full memory barrier since
 * the end of its last corresponding SRCU-sched read-side critical section
 * whose beginning preceded the call to synchronize_srcu().  In addition,
 * each CPU having an SRCU read-side critical section that extends beyond
 * the return from synchronize_srcu() is guaranteed to have executed a
 * full memory barrier after the beginning of synchronize_srcu() and before
 * the beginning of that SRCU 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_srcu(), 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_srcu().  This guarantee applies even if CPU A and CPU B
 * are the same CPU, but again only if the system has more than one CPU.
 *
 * Of course, these memory-ordering guarantees apply only when
 * synchronize_srcu(), srcu_read_lock(), and srcu_read_unlock() are
 * passed the same srcu_struct structure.
924 925 926 927 928
 *
 * If SRCU is likely idle, expedite the first request.  This semantic
 * was provided by Classic SRCU, and is relied upon by its users, so TREE
 * SRCU must also provide it.  Note that detecting idleness is heuristic
 * and subject to both false positives and negatives.
929 930 931
 */
void synchronize_srcu(struct srcu_struct *sp)
{
932
	if (srcu_might_be_idle(sp) || rcu_gp_is_expedited())
933 934
		synchronize_srcu_expedited(sp);
	else
935
		__synchronize_srcu(sp, true);
936 937 938
}
EXPORT_SYMBOL_GPL(synchronize_srcu);

939 940 941 942 943 944 945 946 947 948 949 950 951 952
/*
 * Callback function for srcu_barrier() use.
 */
static void srcu_barrier_cb(struct rcu_head *rhp)
{
	struct srcu_data *sdp;
	struct srcu_struct *sp;

	sdp = container_of(rhp, struct srcu_data, srcu_barrier_head);
	sp = sdp->sp;
	if (atomic_dec_and_test(&sp->srcu_barrier_cpu_cnt))
		complete(&sp->srcu_barrier_completion);
}

953 954 955 956 957 958
/**
 * srcu_barrier - Wait until all in-flight call_srcu() callbacks complete.
 * @sp: srcu_struct on which to wait for in-flight callbacks.
 */
void srcu_barrier(struct srcu_struct *sp)
{
959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988
	int cpu;
	struct srcu_data *sdp;
	unsigned long s = rcu_seq_snap(&sp->srcu_barrier_seq);

	check_init_srcu_struct(sp);
	mutex_lock(&sp->srcu_barrier_mutex);
	if (rcu_seq_done(&sp->srcu_barrier_seq, s)) {
		smp_mb(); /* Force ordering following return. */
		mutex_unlock(&sp->srcu_barrier_mutex);
		return; /* Someone else did our work for us. */
	}
	rcu_seq_start(&sp->srcu_barrier_seq);
	init_completion(&sp->srcu_barrier_completion);

	/* Initial count prevents reaching zero until all CBs are posted. */
	atomic_set(&sp->srcu_barrier_cpu_cnt, 1);

	/*
	 * Each pass through this loop enqueues a callback, but only
	 * on CPUs already having callbacks enqueued.  Note that if
	 * a CPU already has callbacks enqueue, it must have already
	 * registered the need for a future grace period, so all we
	 * need do is enqueue a callback that will use the same
	 * grace period as the last callback already in the queue.
	 */
	for_each_possible_cpu(cpu) {
		sdp = per_cpu_ptr(sp->sda, cpu);
		spin_lock_irq(&sdp->lock);
		atomic_inc(&sp->srcu_barrier_cpu_cnt);
		sdp->srcu_barrier_head.func = srcu_barrier_cb;
989
		debug_rcu_head_queue(&sdp->srcu_barrier_head);
990
		if (!rcu_segcblist_entrain(&sdp->srcu_cblist,
991 992
					   &sdp->srcu_barrier_head, 0)) {
			debug_rcu_head_unqueue(&sdp->srcu_barrier_head);
993
			atomic_dec(&sp->srcu_barrier_cpu_cnt);
994
		}
995 996 997 998 999 1000 1001 1002 1003 1004
		spin_unlock_irq(&sdp->lock);
	}

	/* Remove the initial count, at which point reaching zero can happen. */
	if (atomic_dec_and_test(&sp->srcu_barrier_cpu_cnt))
		complete(&sp->srcu_barrier_completion);
	wait_for_completion(&sp->srcu_barrier_completion);

	rcu_seq_end(&sp->srcu_barrier_seq);
	mutex_unlock(&sp->srcu_barrier_mutex);
1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016
}
EXPORT_SYMBOL_GPL(srcu_barrier);

/**
 * srcu_batches_completed - return batches completed.
 * @sp: srcu_struct on which to report batch completion.
 *
 * Report the number of batches, correlated with, but not necessarily
 * precisely the same as, the number of grace periods that have elapsed.
 */
unsigned long srcu_batches_completed(struct srcu_struct *sp)
{
1017
	return sp->srcu_idx;
1018 1019 1020 1021
}
EXPORT_SYMBOL_GPL(srcu_batches_completed);

/*
1022 1023 1024
 * Core SRCU state machine.  Push state bits of ->srcu_gp_seq
 * to SRCU_STATE_SCAN2, and invoke srcu_gp_end() when scan has
 * completed in that state.
1025
 */
1026
static void srcu_advance_state(struct srcu_struct *sp)
1027 1028 1029
{
	int idx;

1030 1031
	mutex_lock(&sp->srcu_gp_mutex);

1032 1033
	/*
	 * Because readers might be delayed for an extended period after
1034
	 * fetching ->srcu_idx for their index, at any point in time there
1035 1036 1037 1038 1039 1040 1041 1042 1043
	 * might well be readers using both idx=0 and idx=1.  We therefore
	 * need to wait for readers to clear from both index values before
	 * invoking a callback.
	 *
	 * The load-acquire ensures that we see the accesses performed
	 * by the prior grace period.
	 */
	idx = rcu_seq_state(smp_load_acquire(&sp->srcu_gp_seq)); /* ^^^ */
	if (idx == SRCU_STATE_IDLE) {
1044 1045 1046 1047 1048
		spin_lock_irq(&sp->gp_lock);
		if (ULONG_CMP_GE(sp->srcu_gp_seq, sp->srcu_gp_seq_needed)) {
			WARN_ON_ONCE(rcu_seq_state(sp->srcu_gp_seq));
			spin_unlock_irq(&sp->gp_lock);
			mutex_unlock(&sp->srcu_gp_mutex);
1049 1050 1051 1052 1053
			return;
		}
		idx = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
		if (idx == SRCU_STATE_IDLE)
			srcu_gp_start(sp);
1054 1055 1056
		spin_unlock_irq(&sp->gp_lock);
		if (idx != SRCU_STATE_IDLE) {
			mutex_unlock(&sp->srcu_gp_mutex);
1057
			return; /* Someone else started the grace period. */
1058
		}
1059 1060 1061
	}

	if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_SCAN1) {
1062 1063 1064
		idx = 1 ^ (sp->srcu_idx & 1);
		if (!try_check_zero(sp, idx, 1)) {
			mutex_unlock(&sp->srcu_gp_mutex);
1065
			return; /* readers present, retry later. */
1066
		}
1067 1068 1069 1070 1071 1072 1073 1074 1075 1076
		srcu_flip(sp);
		rcu_seq_set_state(&sp->srcu_gp_seq, SRCU_STATE_SCAN2);
	}

	if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_SCAN2) {

		/*
		 * SRCU read-side critical sections are normally short,
		 * so check at least twice in quick succession after a flip.
		 */
1077 1078 1079 1080 1081 1082
		idx = 1 ^ (sp->srcu_idx & 1);
		if (!try_check_zero(sp, idx, 2)) {
			mutex_unlock(&sp->srcu_gp_mutex);
			return; /* readers present, retry later. */
		}
		srcu_gp_end(sp);  /* Releases ->srcu_gp_mutex. */
1083 1084 1085 1086 1087 1088 1089 1090 1091
	}
}

/*
 * Invoke a limited number of SRCU callbacks that have passed through
 * their grace period.  If there are more to do, SRCU will reschedule
 * the workqueue.  Note that needed memory barriers have been executed
 * in this task's context by srcu_readers_active_idx_check().
 */
1092
static void srcu_invoke_callbacks(struct work_struct *work)
1093
{
1094
	bool more;
1095 1096
	struct rcu_cblist ready_cbs;
	struct rcu_head *rhp;
1097 1098
	struct srcu_data *sdp;
	struct srcu_struct *sp;
1099

1100 1101
	sdp = container_of(work, struct srcu_data, work.work);
	sp = sdp->sp;
1102
	rcu_cblist_init(&ready_cbs);
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	spin_lock_irq(&sdp->lock);
	smp_mb(); /* Old grace periods before callback invocation! */
	rcu_segcblist_advance(&sdp->srcu_cblist,
			      rcu_seq_current(&sp->srcu_gp_seq));
	if (sdp->srcu_cblist_invoking ||
	    !rcu_segcblist_ready_cbs(&sdp->srcu_cblist)) {
		spin_unlock_irq(&sdp->lock);
		return;  /* Someone else on the job or nothing to do. */
	}

	/* We are on the job!  Extract and invoke ready callbacks. */
	sdp->srcu_cblist_invoking = true;
	rcu_segcblist_extract_done_cbs(&sdp->srcu_cblist, &ready_cbs);
	spin_unlock_irq(&sdp->lock);
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	rhp = rcu_cblist_dequeue(&ready_cbs);
	for (; rhp != NULL; rhp = rcu_cblist_dequeue(&ready_cbs)) {
1119
		debug_rcu_head_unqueue(rhp);
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		local_bh_disable();
		rhp->func(rhp);
		local_bh_enable();
	}
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	/*
	 * Update counts, accelerate new callbacks, and if needed,
	 * schedule another round of callback invocation.
	 */
	spin_lock_irq(&sdp->lock);
	rcu_segcblist_insert_count(&sdp->srcu_cblist, &ready_cbs);
	(void)rcu_segcblist_accelerate(&sdp->srcu_cblist,
				       rcu_seq_snap(&sp->srcu_gp_seq));
	sdp->srcu_cblist_invoking = false;
	more = rcu_segcblist_ready_cbs(&sdp->srcu_cblist);
	spin_unlock_irq(&sdp->lock);
	if (more)
		srcu_schedule_cbs_sdp(sdp, 0);
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}

/*
 * Finished one round of SRCU grace period.  Start another if there are
 * more SRCU callbacks queued, otherwise put SRCU into not-running state.
 */
static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay)
{
1146
	bool pushgp = true;
1147

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	spin_lock_irq(&sp->gp_lock);
	if (ULONG_CMP_GE(sp->srcu_gp_seq, sp->srcu_gp_seq_needed)) {
		if (!WARN_ON_ONCE(rcu_seq_state(sp->srcu_gp_seq))) {
			/* All requests fulfilled, time to go idle. */
			pushgp = false;
		}
	} else if (!rcu_seq_state(sp->srcu_gp_seq)) {
		/* Outstanding request and no GP.  Start one. */
		srcu_gp_start(sp);
1157
	}
1158
	spin_unlock_irq(&sp->gp_lock);
1159

1160
	if (pushgp)
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		queue_delayed_work(system_power_efficient_wq, &sp->work, delay);
}

/*
 * This is the work-queue function that handles SRCU grace periods.
 */
void process_srcu(struct work_struct *work)
{
	struct srcu_struct *sp;

	sp = container_of(work, struct srcu_struct, work.work);

1173
	srcu_advance_state(sp);
1174
	srcu_reschedule(sp, srcu_get_delay(sp));
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}
EXPORT_SYMBOL_GPL(process_srcu);
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void srcutorture_get_gp_data(enum rcutorture_type test_type,
1179 1180
			     struct srcu_struct *sp, int *flags,
			     unsigned long *gpnum, unsigned long *completed)
1181 1182 1183 1184 1185 1186 1187 1188
{
	if (test_type != SRCU_FLAVOR)
		return;
	*flags = 0;
	*completed = rcu_seq_ctr(sp->srcu_gp_seq);
	*gpnum = rcu_seq_ctr(sp->srcu_gp_seq_needed);
}
EXPORT_SYMBOL_GPL(srcutorture_get_gp_data);
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static int __init srcu_bootup_announce(void)
{
	pr_info("Hierarchical SRCU implementation.\n");
1193 1194
	if (exp_holdoff != DEFAULT_SRCU_EXP_HOLDOFF)
		pr_info("\tNon-default auto-expedite holdoff of %lu ns.\n", exp_holdoff);
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	return 0;
}
early_initcall(srcu_bootup_announce);