tree_plugin.h 89.6 KB
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/*
 * Read-Copy Update mechanism for mutual exclusion (tree-based version)
 * Internal non-public definitions that provide either classic
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 * or preemptible semantics.
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 *
 * 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 Red Hat, 2009
 * Copyright IBM Corporation, 2009
 *
 * Author: Ingo Molnar <mingo@elte.hu>
 *	   Paul E. McKenney <paulmck@linux.vnet.ibm.com>
 */

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#include <linux/delay.h>
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#include <linux/gfp.h>
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#include <linux/oom.h>
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#include <linux/smpboot.h>
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#include "../time/tick-internal.h"
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#ifdef CONFIG_RCU_BOOST
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#include "../locking/rtmutex_common.h"
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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);
DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
DEFINE_PER_CPU(char, rcu_cpu_has_work);

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#endif /* #ifdef CONFIG_RCU_BOOST */
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#ifdef CONFIG_RCU_NOCB_CPU
static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
static bool have_rcu_nocb_mask;	    /* Was rcu_nocb_mask allocated? */
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static bool __read_mostly rcu_nocb_poll;    /* Offload kthread are to poll. */
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#endif /* #ifdef CONFIG_RCU_NOCB_CPU */

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/*
 * Check the RCU kernel configuration parameters and print informative
 * messages about anything out of the ordinary.  If you like #ifdef, you
 * will love this function.
 */
static void __init rcu_bootup_announce_oddness(void)
{
#ifdef CONFIG_RCU_TRACE
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	pr_info("\tRCU debugfs-based tracing is enabled.\n");
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#endif
#if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32)
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	pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
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	       CONFIG_RCU_FANOUT);
#endif
#ifdef CONFIG_RCU_FANOUT_EXACT
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	pr_info("\tHierarchical RCU autobalancing is disabled.\n");
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#endif
#ifdef CONFIG_RCU_FAST_NO_HZ
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	pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
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#endif
#ifdef CONFIG_PROVE_RCU
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	pr_info("\tRCU lockdep checking is enabled.\n");
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#endif
#ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE
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	pr_info("\tRCU torture testing starts during boot.\n");
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#endif
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#if defined(CONFIG_RCU_CPU_STALL_INFO)
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	pr_info("\tAdditional per-CPU info printed with stalls.\n");
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#endif
#if NUM_RCU_LVL_4 != 0
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	pr_info("\tFour-level hierarchy is enabled.\n");
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#endif
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	if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF)
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		pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
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	if (nr_cpu_ids != NR_CPUS)
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		pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);
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#ifdef CONFIG_RCU_BOOST
	pr_info("\tRCU kthread priority: %d.\n", kthread_prio);
#endif
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}

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#ifdef CONFIG_PREEMPT_RCU
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RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu);
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static struct rcu_state *rcu_state_p = &rcu_preempt_state;
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static int rcu_preempted_readers_exp(struct rcu_node *rnp);
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static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
			       bool wake);
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/*
 * Tell them what RCU they are running.
 */
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static void __init rcu_bootup_announce(void)
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{
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	pr_info("Preemptible hierarchical RCU implementation.\n");
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	rcu_bootup_announce_oddness();
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}

/*
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 * Record a preemptible-RCU quiescent state for the specified CPU.  Note
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 * that this just means that the task currently running on the CPU is
 * not in a quiescent state.  There might be any number of tasks blocked
 * while in an RCU read-side critical section.
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 *
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 * As with the other rcu_*_qs() functions, callers to this function
 * must disable preemption.
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 */
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static void rcu_preempt_qs(void)
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{
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	if (!__this_cpu_read(rcu_preempt_data.passed_quiesce)) {
		trace_rcu_grace_period(TPS("rcu_preempt"),
				       __this_cpu_read(rcu_preempt_data.gpnum),
				       TPS("cpuqs"));
		__this_cpu_write(rcu_preempt_data.passed_quiesce, 1);
		barrier(); /* Coordinate with rcu_preempt_check_callbacks(). */
		current->rcu_read_unlock_special.b.need_qs = false;
	}
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}

/*
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 * We have entered the scheduler, and the current task might soon be
 * context-switched away from.  If this task is in an RCU read-side
 * critical section, we will no longer be able to rely on the CPU to
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 * record that fact, so we enqueue the task on the blkd_tasks list.
 * The task will dequeue itself when it exits the outermost enclosing
 * RCU read-side critical section.  Therefore, the current grace period
 * cannot be permitted to complete until the blkd_tasks list entries
 * predating the current grace period drain, in other words, until
 * rnp->gp_tasks becomes NULL.
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 *
 * Caller must disable preemption.
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 */
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static void rcu_preempt_note_context_switch(void)
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{
	struct task_struct *t = current;
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	unsigned long flags;
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	struct rcu_data *rdp;
	struct rcu_node *rnp;

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	if (t->rcu_read_lock_nesting > 0 &&
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	    !t->rcu_read_unlock_special.b.blocked) {
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		/* Possibly blocking in an RCU read-side critical section. */
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		rdp = this_cpu_ptr(rcu_preempt_state.rda);
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		rnp = rdp->mynode;
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		raw_spin_lock_irqsave(&rnp->lock, flags);
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		smp_mb__after_unlock_lock();
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		t->rcu_read_unlock_special.b.blocked = true;
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		t->rcu_blocked_node = rnp;
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		/*
		 * If this CPU has already checked in, then this task
		 * will hold up the next grace period rather than the
		 * current grace period.  Queue the task accordingly.
		 * If the task is queued for the current grace period
		 * (i.e., this CPU has not yet passed through a quiescent
		 * state for the current grace period), then as long
		 * as that task remains queued, the current grace period
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		 * cannot end.  Note that there is some uncertainty as
		 * to exactly when the current grace period started.
		 * We take a conservative approach, which can result
		 * in unnecessarily waiting on tasks that started very
		 * slightly after the current grace period began.  C'est
		 * la vie!!!
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		 *
		 * But first, note that the current CPU must still be
		 * on line!
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		 */
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		WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0);
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		WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
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		if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) {
			list_add(&t->rcu_node_entry, rnp->gp_tasks->prev);
			rnp->gp_tasks = &t->rcu_node_entry;
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#ifdef CONFIG_RCU_BOOST
			if (rnp->boost_tasks != NULL)
				rnp->boost_tasks = rnp->gp_tasks;
#endif /* #ifdef CONFIG_RCU_BOOST */
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		} else {
			list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
			if (rnp->qsmask & rdp->grpmask)
				rnp->gp_tasks = &t->rcu_node_entry;
		}
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		trace_rcu_preempt_task(rdp->rsp->name,
				       t->pid,
				       (rnp->qsmask & rdp->grpmask)
				       ? rnp->gpnum
				       : rnp->gpnum + 1);
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		raw_spin_unlock_irqrestore(&rnp->lock, flags);
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	} else if (t->rcu_read_lock_nesting < 0 &&
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		   t->rcu_read_unlock_special.s) {
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		/*
		 * Complete exit from RCU read-side critical section on
		 * behalf of preempted instance of __rcu_read_unlock().
		 */
		rcu_read_unlock_special(t);
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	}

	/*
	 * Either we were not in an RCU read-side critical section to
	 * begin with, or we have now recorded that critical section
	 * globally.  Either way, we can now note a quiescent state
	 * for this CPU.  Again, if we were in an RCU read-side critical
	 * section, and if that critical section was blocking the current
	 * grace period, then the fact that the task has been enqueued
	 * means that we continue to block the current grace period.
	 */
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	rcu_preempt_qs();
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}

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/*
 * Check for preempted RCU readers blocking the current grace period
 * for the specified rcu_node structure.  If the caller needs a reliable
 * answer, it must hold the rcu_node's ->lock.
 */
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static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
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{
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	return rnp->gp_tasks != NULL;
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}

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/*
 * Record a quiescent state for all tasks that were previously queued
 * on the specified rcu_node structure and that were blocking the current
 * RCU grace period.  The caller must hold the specified rnp->lock with
 * irqs disabled, and this lock is released upon return, but irqs remain
 * disabled.
 */
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static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
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	__releases(rnp->lock)
{
	unsigned long mask;
	struct rcu_node *rnp_p;

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

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

	/* Report up the rest of the hierarchy. */
	mask = rnp->grpmask;
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	raw_spin_unlock(&rnp->lock);	/* irqs remain disabled. */
	raw_spin_lock(&rnp_p->lock);	/* irqs already disabled. */
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	smp_mb__after_unlock_lock();
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	rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags);
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}

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/*
 * Advance a ->blkd_tasks-list pointer to the next entry, instead
 * returning NULL if at the end of the list.
 */
static struct list_head *rcu_next_node_entry(struct task_struct *t,
					     struct rcu_node *rnp)
{
	struct list_head *np;

	np = t->rcu_node_entry.next;
	if (np == &rnp->blkd_tasks)
		np = NULL;
	return np;
}

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/*
 * Return true if the specified rcu_node structure has tasks that were
 * preempted within an RCU read-side critical section.
 */
static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
{
	return !list_empty(&rnp->blkd_tasks);
}

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/*
 * Handle special cases during rcu_read_unlock(), such as needing to
 * notify RCU core processing or task having blocked during the RCU
 * read-side critical section.
 */
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void rcu_read_unlock_special(struct task_struct *t)
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{
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	bool empty;
	bool empty_exp;
	bool empty_norm;
	bool empty_exp_now;
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	unsigned long flags;
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	struct list_head *np;
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#ifdef CONFIG_RCU_BOOST
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	bool drop_boost_mutex = false;
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#endif /* #ifdef CONFIG_RCU_BOOST */
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	struct rcu_node *rnp;
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	union rcu_special special;
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	/* NMI handlers cannot block and cannot safely manipulate state. */
	if (in_nmi())
		return;

	local_irq_save(flags);

	/*
	 * If RCU core is waiting for this CPU to exit critical section,
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	 * let it know that we have done so.  Because irqs are disabled,
	 * t->rcu_read_unlock_special cannot change.
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	 */
	special = t->rcu_read_unlock_special;
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	if (special.b.need_qs) {
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		rcu_preempt_qs();
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		t->rcu_read_unlock_special.b.need_qs = false;
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		if (!t->rcu_read_unlock_special.s) {
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			local_irq_restore(flags);
			return;
		}
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	}

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	/* Hardware IRQ handlers cannot block, complain if they get here. */
	if (WARN_ON_ONCE(in_irq() || in_serving_softirq())) {
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		local_irq_restore(flags);
		return;
	}

	/* Clean up if blocked during RCU read-side critical section. */
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	if (special.b.blocked) {
		t->rcu_read_unlock_special.b.blocked = false;
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		/*
		 * Remove this task from the list it blocked on.  The
		 * task can migrate while we acquire the lock, but at
		 * most one time.  So at most two passes through loop.
		 */
		for (;;) {
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			rnp = t->rcu_blocked_node;
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			raw_spin_lock(&rnp->lock);  /* irqs already disabled. */
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			smp_mb__after_unlock_lock();
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			if (rnp == t->rcu_blocked_node)
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				break;
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			raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
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		}
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		empty = !rcu_preempt_has_tasks(rnp);
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		empty_norm = !rcu_preempt_blocked_readers_cgp(rnp);
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		empty_exp = !rcu_preempted_readers_exp(rnp);
		smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
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		np = rcu_next_node_entry(t, rnp);
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		list_del_init(&t->rcu_node_entry);
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		t->rcu_blocked_node = NULL;
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		trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
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						rnp->gpnum, t->pid);
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		if (&t->rcu_node_entry == rnp->gp_tasks)
			rnp->gp_tasks = np;
		if (&t->rcu_node_entry == rnp->exp_tasks)
			rnp->exp_tasks = np;
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#ifdef CONFIG_RCU_BOOST
		if (&t->rcu_node_entry == rnp->boost_tasks)
			rnp->boost_tasks = np;
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		/* Snapshot ->boost_mtx ownership with rcu_node lock held. */
		drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
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#endif /* #ifdef CONFIG_RCU_BOOST */
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		/*
		 * If this was the last task on the list, go see if we
		 * need to propagate ->qsmaskinit bit clearing up the
		 * rcu_node tree.
		 */
		if (!empty && !rcu_preempt_has_tasks(rnp))
			rcu_cleanup_dead_rnp(rnp);

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		/*
		 * If this was the last task on the current list, and if
		 * we aren't waiting on any CPUs, report the quiescent state.
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		 * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
		 * so we must take a snapshot of the expedited state.
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		 */
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		empty_exp_now = !rcu_preempted_readers_exp(rnp);
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		if (!empty_norm && !rcu_preempt_blocked_readers_cgp(rnp)) {
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			trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
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							 rnp->gpnum,
							 0, rnp->qsmask,
							 rnp->level,
							 rnp->grplo,
							 rnp->grphi,
							 !!rnp->gp_tasks);
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			rcu_report_unblock_qs_rnp(rnp, flags);
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		} else {
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			raw_spin_unlock_irqrestore(&rnp->lock, flags);
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		}
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#ifdef CONFIG_RCU_BOOST
		/* Unboost if we were boosted. */
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		if (drop_boost_mutex)
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			rt_mutex_unlock(&rnp->boost_mtx);
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#endif /* #ifdef CONFIG_RCU_BOOST */

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		/*
		 * If this was the last task on the expedited lists,
		 * then we need to report up the rcu_node hierarchy.
		 */
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		if (!empty_exp && empty_exp_now)
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			rcu_report_exp_rnp(&rcu_preempt_state, rnp, true);
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	} else {
		local_irq_restore(flags);
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	}
}

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/*
 * Dump detailed information for all tasks blocking the current RCU
 * grace period on the specified rcu_node structure.
 */
static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
{
	unsigned long flags;
	struct task_struct *t;

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	raw_spin_lock_irqsave(&rnp->lock, flags);
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	if (!rcu_preempt_blocked_readers_cgp(rnp)) {
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
		return;
	}
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	t = list_entry(rnp->gp_tasks,
		       struct task_struct, rcu_node_entry);
	list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry)
		sched_show_task(t);
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
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}

/*
 * Dump detailed information for all tasks blocking the current RCU
 * grace period.
 */
static void rcu_print_detail_task_stall(struct rcu_state *rsp)
{
	struct rcu_node *rnp = rcu_get_root(rsp);

	rcu_print_detail_task_stall_rnp(rnp);
	rcu_for_each_leaf_node(rsp, rnp)
		rcu_print_detail_task_stall_rnp(rnp);
}

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#ifdef CONFIG_RCU_CPU_STALL_INFO

static void rcu_print_task_stall_begin(struct rcu_node *rnp)
{
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	pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
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	       rnp->level, rnp->grplo, rnp->grphi);
}

static void rcu_print_task_stall_end(void)
{
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	pr_cont("\n");
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}

#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */

static void rcu_print_task_stall_begin(struct rcu_node *rnp)
{
}

static void rcu_print_task_stall_end(void)
{
}

#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */

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/*
 * Scan the current list of tasks blocked within RCU read-side critical
 * sections, printing out the tid of each.
 */
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static int rcu_print_task_stall(struct rcu_node *rnp)
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{
	struct task_struct *t;
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	int ndetected = 0;
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	if (!rcu_preempt_blocked_readers_cgp(rnp))
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		return 0;
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	rcu_print_task_stall_begin(rnp);
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	t = list_entry(rnp->gp_tasks,
		       struct task_struct, rcu_node_entry);
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	list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
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		pr_cont(" P%d", t->pid);
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		ndetected++;
	}
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	rcu_print_task_stall_end();
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	return ndetected;
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}

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/*
 * Check that the list of blocked tasks for the newly completed grace
 * period is in fact empty.  It is a serious bug to complete a grace
 * period that still has RCU readers blocked!  This function must be
 * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
 * must be held by the caller.
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 *
 * Also, if there are blocked tasks on the list, they automatically
 * block the newly created grace period, so set up ->gp_tasks accordingly.
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 */
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
{
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	WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
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	if (rcu_preempt_has_tasks(rnp))
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		rnp->gp_tasks = rnp->blkd_tasks.next;
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	WARN_ON_ONCE(rnp->qsmask);
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}

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#ifdef CONFIG_HOTPLUG_CPU

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#endif /* #ifdef CONFIG_HOTPLUG_CPU */

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/*
 * Check for a quiescent state from the current CPU.  When a task blocks,
 * the task is recorded in the corresponding CPU's rcu_node structure,
 * which is checked elsewhere.
 *
 * Caller must disable hard irqs.
 */
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static void rcu_preempt_check_callbacks(void)
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{
	struct task_struct *t = current;

	if (t->rcu_read_lock_nesting == 0) {
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		rcu_preempt_qs();
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		return;
	}
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	if (t->rcu_read_lock_nesting > 0 &&
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	    __this_cpu_read(rcu_preempt_data.qs_pending) &&
	    !__this_cpu_read(rcu_preempt_data.passed_quiesce))
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		t->rcu_read_unlock_special.b.need_qs = true;
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}

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#ifdef CONFIG_RCU_BOOST

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static void rcu_preempt_do_callbacks(void)
{
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	rcu_do_batch(&rcu_preempt_state, this_cpu_ptr(&rcu_preempt_data));
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}

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#endif /* #ifdef CONFIG_RCU_BOOST */

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/*
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 * Queue a preemptible-RCU callback for invocation after a grace period.
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 */
void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
{
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	__call_rcu(head, func, &rcu_preempt_state, -1, 0);
563 564 565
}
EXPORT_SYMBOL_GPL(call_rcu);

566 567 568 569 570
/**
 * synchronize_rcu - wait until a grace period has elapsed.
 *
 * Control will return to the caller some time after a full grace
 * period has elapsed, in other words after all currently executing RCU
571 572 573 574 575
 * read-side critical sections have completed.  Note, however, that
 * upon return from synchronize_rcu(), the caller might well be executing
 * concurrently with new RCU read-side critical sections that began while
 * synchronize_rcu() was waiting.  RCU read-side critical sections are
 * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
576 577 578
 *
 * See the description of synchronize_sched() for more detailed information
 * on memory ordering guarantees.
579 580 581
 */
void synchronize_rcu(void)
{
582 583 584 585
	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() in RCU read-side critical section");
586 587
	if (!rcu_scheduler_active)
		return;
588 589 590 591
	if (rcu_expedited)
		synchronize_rcu_expedited();
	else
		wait_rcu_gp(call_rcu);
592 593 594
}
EXPORT_SYMBOL_GPL(synchronize_rcu);

595
static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
596
static unsigned long sync_rcu_preempt_exp_count;
597 598 599 600 601 602 603 604 605 606
static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);

/*
 * Return non-zero if there are any tasks in RCU read-side critical
 * sections blocking the current preemptible-RCU expedited grace period.
 * If there is no preemptible-RCU expedited grace period currently in
 * progress, returns zero unconditionally.
 */
static int rcu_preempted_readers_exp(struct rcu_node *rnp)
{
607
	return rnp->exp_tasks != NULL;
608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632
}

/*
 * return non-zero if there is no RCU expedited grace period in progress
 * for the specified rcu_node structure, in other words, if all CPUs and
 * tasks covered by the specified rcu_node structure have done their bit
 * for the current expedited grace period.  Works only for preemptible
 * RCU -- other RCU implementation use other means.
 *
 * Caller must hold sync_rcu_preempt_exp_mutex.
 */
static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
{
	return !rcu_preempted_readers_exp(rnp) &&
	       ACCESS_ONCE(rnp->expmask) == 0;
}

/*
 * Report the exit from RCU read-side critical section for the last task
 * that queued itself during or before the current expedited preemptible-RCU
 * grace period.  This event is reported either to the rcu_node structure on
 * which the task was queued or to one of that rcu_node structure's ancestors,
 * recursively up the tree.  (Calm down, calm down, we do the recursion
 * iteratively!)
 *
633 634 635
 * Most callers will set the "wake" flag, but the task initiating the
 * expedited grace period need not wake itself.
 *
636 637
 * Caller must hold sync_rcu_preempt_exp_mutex.
 */
638 639
static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
			       bool wake)
640 641 642 643
{
	unsigned long flags;
	unsigned long mask;

P
Paul E. McKenney 已提交
644
	raw_spin_lock_irqsave(&rnp->lock, flags);
645
	smp_mb__after_unlock_lock();
646
	for (;;) {
647 648
		if (!sync_rcu_preempt_exp_done(rnp)) {
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
649
			break;
650
		}
651
		if (rnp->parent == NULL) {
652
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
653 654
			if (wake) {
				smp_mb(); /* EGP done before wake_up(). */
655
				wake_up(&sync_rcu_preempt_exp_wq);
656
			}
657 658 659
			break;
		}
		mask = rnp->grpmask;
P
Paul E. McKenney 已提交
660
		raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
661
		rnp = rnp->parent;
P
Paul E. McKenney 已提交
662
		raw_spin_lock(&rnp->lock); /* irqs already disabled */
663
		smp_mb__after_unlock_lock();
664 665 666 667 668 669 670 671 672
		rnp->expmask &= ~mask;
	}
}

/*
 * Snapshot the tasks blocking the newly started preemptible-RCU expedited
 * grace period for the specified rcu_node structure.  If there are no such
 * tasks, report it up the rcu_node hierarchy.
 *
673 674
 * Caller must hold sync_rcu_preempt_exp_mutex and must exclude
 * CPU hotplug operations.
675 676 677 678
 */
static void
sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
{
679
	unsigned long flags;
680
	int must_wait = 0;
681

682
	raw_spin_lock_irqsave(&rnp->lock, flags);
683
	smp_mb__after_unlock_lock();
684
	if (!rcu_preempt_has_tasks(rnp)) {
685
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
686
	} else {
687
		rnp->exp_tasks = rnp->blkd_tasks.next;
688
		rcu_initiate_boost(rnp, flags);  /* releases rnp->lock */
689 690
		must_wait = 1;
	}
691
	if (!must_wait)
692
		rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */
693 694
}

695 696 697 698 699 700 701 702 703 704 705
/**
 * synchronize_rcu_expedited - Brute-force RCU grace period
 *
 * Wait for an RCU-preempt grace period, but expedite it.  The basic
 * idea is to invoke synchronize_sched_expedited() to push all the tasks to
 * the ->blkd_tasks lists and wait for this list to drain.  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_rcu_expedited() in a loop,
 * please restructure your code to batch your updates, and then Use a
 * single synchronize_rcu() instead.
706 707 708
 */
void synchronize_rcu_expedited(void)
{
709 710 711
	unsigned long flags;
	struct rcu_node *rnp;
	struct rcu_state *rsp = &rcu_preempt_state;
712
	unsigned long snap;
713 714 715 716 717 718
	int trycount = 0;

	smp_mb(); /* Caller's modifications seen first by other CPUs. */
	snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1;
	smp_mb(); /* Above access cannot bleed into critical section. */

719 720 721 722 723 724 725 726
	/*
	 * Block CPU-hotplug operations.  This means that any CPU-hotplug
	 * operation that finds an rcu_node structure with tasks in the
	 * process of being boosted will know that all tasks blocking
	 * this expedited grace period will already be in the process of
	 * being boosted.  This simplifies the process of moving tasks
	 * from leaf to root rcu_node structures.
	 */
727 728 729 730 731
	if (!try_get_online_cpus()) {
		/* CPU-hotplug operation in flight, fall back to normal GP. */
		wait_rcu_gp(call_rcu);
		return;
	}
732

733 734 735 736 737 738
	/*
	 * Acquire lock, falling back to synchronize_rcu() if too many
	 * lock-acquisition failures.  Of course, if someone does the
	 * expedited grace period for us, just leave.
	 */
	while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) {
739 740 741 742 743
		if (ULONG_CMP_LT(snap,
		    ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
			put_online_cpus();
			goto mb_ret; /* Others did our work for us. */
		}
744
		if (trycount++ < 10) {
745
			udelay(trycount * num_online_cpus());
746
		} else {
747
			put_online_cpus();
748
			wait_rcu_gp(call_rcu);
749 750 751
			return;
		}
	}
752 753
	if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
		put_online_cpus();
754
		goto unlock_mb_ret; /* Others did our work for us. */
755
	}
756

757
	/* force all RCU readers onto ->blkd_tasks lists. */
758 759 760 761
	synchronize_sched_expedited();

	/* Initialize ->expmask for all non-leaf rcu_node structures. */
	rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) {
762
		raw_spin_lock_irqsave(&rnp->lock, flags);
763
		smp_mb__after_unlock_lock();
764
		rnp->expmask = rnp->qsmaskinit;
765
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
766 767
	}

768
	/* Snapshot current state of ->blkd_tasks lists. */
769 770 771 772 773
	rcu_for_each_leaf_node(rsp, rnp)
		sync_rcu_preempt_exp_init(rsp, rnp);
	if (NUM_RCU_NODES > 1)
		sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp));

774
	put_online_cpus();
775

776
	/* Wait for snapshotted ->blkd_tasks lists to drain. */
777 778 779 780 781 782
	rnp = rcu_get_root(rsp);
	wait_event(sync_rcu_preempt_exp_wq,
		   sync_rcu_preempt_exp_done(rnp));

	/* Clean up and exit. */
	smp_mb(); /* ensure expedited GP seen before counter increment. */
783 784
	ACCESS_ONCE(sync_rcu_preempt_exp_count) =
					sync_rcu_preempt_exp_count + 1;
785 786 787 788
unlock_mb_ret:
	mutex_unlock(&sync_rcu_preempt_exp_mutex);
mb_ret:
	smp_mb(); /* ensure subsequent action seen after grace period. */
789 790 791
}
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);

792 793
/**
 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
794 795 796 797 798
 *
 * Note that this primitive does not necessarily wait for an RCU grace period
 * to complete.  For example, if there are no RCU callbacks queued anywhere
 * in the system, then rcu_barrier() is within its rights to return
 * immediately, without waiting for anything, much less an RCU grace period.
799 800 801
 */
void rcu_barrier(void)
{
802
	_rcu_barrier(&rcu_preempt_state);
803 804 805
}
EXPORT_SYMBOL_GPL(rcu_barrier);

806
/*
P
Paul E. McKenney 已提交
807
 * Initialize preemptible RCU's state structures.
808 809 810
 */
static void __init __rcu_init_preempt(void)
{
811
	rcu_init_one(&rcu_preempt_state, &rcu_preempt_data);
812 813
}

814 815 816 817 818 819 820 821 822 823 824 825 826 827
/*
 * Check for a task exiting while in a preemptible-RCU read-side
 * critical section, clean up if so.  No need to issue warnings,
 * as debug_check_no_locks_held() already does this if lockdep
 * is enabled.
 */
void exit_rcu(void)
{
	struct task_struct *t = current;

	if (likely(list_empty(&current->rcu_node_entry)))
		return;
	t->rcu_read_lock_nesting = 1;
	barrier();
828
	t->rcu_read_unlock_special.b.blocked = true;
829 830 831
	__rcu_read_unlock();
}

832
#else /* #ifdef CONFIG_PREEMPT_RCU */
833

834
static struct rcu_state *rcu_state_p = &rcu_sched_state;
835

836 837 838
/*
 * Tell them what RCU they are running.
 */
839
static void __init rcu_bootup_announce(void)
840
{
841
	pr_info("Hierarchical RCU implementation.\n");
842
	rcu_bootup_announce_oddness();
843 844
}

845 846 847 848
/*
 * Because preemptible RCU does not exist, we never have to check for
 * CPUs being in quiescent states.
 */
849
static void rcu_preempt_note_context_switch(void)
850 851 852
{
}

853
/*
P
Paul E. McKenney 已提交
854
 * Because preemptible RCU does not exist, there are never any preempted
855 856
 * RCU readers.
 */
857
static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
858 859 860 861
{
	return 0;
}

862 863
#ifdef CONFIG_HOTPLUG_CPU

864 865 866 867
/*
 * Because there is no preemptible RCU, there can be no readers blocked.
 */
static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
868
{
869
	return false;
870 871 872 873
}

#endif /* #ifdef CONFIG_HOTPLUG_CPU */

874
/*
P
Paul E. McKenney 已提交
875
 * Because preemptible RCU does not exist, we never have to check for
876 877 878 879 880 881
 * tasks blocked within RCU read-side critical sections.
 */
static void rcu_print_detail_task_stall(struct rcu_state *rsp)
{
}

882
/*
P
Paul E. McKenney 已提交
883
 * Because preemptible RCU does not exist, we never have to check for
884 885
 * tasks blocked within RCU read-side critical sections.
 */
886
static int rcu_print_task_stall(struct rcu_node *rnp)
887
{
888
	return 0;
889 890
}

891
/*
P
Paul E. McKenney 已提交
892
 * Because there is no preemptible RCU, there can be no readers blocked,
893 894
 * so there is no need to check for blocked tasks.  So check only for
 * bogus qsmask values.
895 896 897
 */
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
{
898
	WARN_ON_ONCE(rnp->qsmask);
899 900
}

901
/*
P
Paul E. McKenney 已提交
902
 * Because preemptible RCU does not exist, it never has any callbacks
903 904
 * to check.
 */
905
static void rcu_preempt_check_callbacks(void)
906 907 908
{
}

909 910
/*
 * Wait for an rcu-preempt grace period, but make it happen quickly.
P
Paul E. McKenney 已提交
911
 * But because preemptible RCU does not exist, map to rcu-sched.
912 913 914 915 916 917 918
 */
void synchronize_rcu_expedited(void)
{
	synchronize_sched_expedited();
}
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);

919
/*
P
Paul E. McKenney 已提交
920
 * Because preemptible RCU does not exist, rcu_barrier() is just
921 922 923 924 925 926 927 928
 * another name for rcu_barrier_sched().
 */
void rcu_barrier(void)
{
	rcu_barrier_sched();
}
EXPORT_SYMBOL_GPL(rcu_barrier);

929
/*
P
Paul E. McKenney 已提交
930
 * Because preemptible RCU does not exist, it need not be initialized.
931 932 933 934 935
 */
static void __init __rcu_init_preempt(void)
{
}

936 937 938 939 940 941 942 943
/*
 * Because preemptible RCU does not exist, tasks cannot possibly exit
 * while in preemptible RCU read-side critical sections.
 */
void exit_rcu(void)
{
}

944
#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
945

946 947
#ifdef CONFIG_RCU_BOOST

948
#include "../locking/rtmutex_common.h"
949

950 951 952 953
#ifdef CONFIG_RCU_TRACE

static void rcu_initiate_boost_trace(struct rcu_node *rnp)
{
954
	if (!rcu_preempt_has_tasks(rnp))
955 956 957 958 959 960 961 962
		rnp->n_balk_blkd_tasks++;
	else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL)
		rnp->n_balk_exp_gp_tasks++;
	else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL)
		rnp->n_balk_boost_tasks++;
	else if (rnp->gp_tasks != NULL && rnp->qsmask != 0)
		rnp->n_balk_notblocked++;
	else if (rnp->gp_tasks != NULL &&
963
		 ULONG_CMP_LT(jiffies, rnp->boost_time))
964 965 966 967 968 969 970 971 972 973 974 975 976
		rnp->n_balk_notyet++;
	else
		rnp->n_balk_nos++;
}

#else /* #ifdef CONFIG_RCU_TRACE */

static void rcu_initiate_boost_trace(struct rcu_node *rnp)
{
}

#endif /* #else #ifdef CONFIG_RCU_TRACE */

T
Thomas Gleixner 已提交
977 978 979 980 981 982 983 984 985 986
static void rcu_wake_cond(struct task_struct *t, int status)
{
	/*
	 * If the thread is yielding, only wake it when this
	 * is invoked from idle
	 */
	if (status != RCU_KTHREAD_YIELDING || is_idle_task(current))
		wake_up_process(t);
}

987 988 989 990 991 992 993 994 995 996 997 998 999 1000
/*
 * Carry out RCU priority boosting on the task indicated by ->exp_tasks
 * or ->boost_tasks, advancing the pointer to the next task in the
 * ->blkd_tasks list.
 *
 * Note that irqs must be enabled: boosting the task can block.
 * Returns 1 if there are more tasks needing to be boosted.
 */
static int rcu_boost(struct rcu_node *rnp)
{
	unsigned long flags;
	struct task_struct *t;
	struct list_head *tb;

1001 1002
	if (ACCESS_ONCE(rnp->exp_tasks) == NULL &&
	    ACCESS_ONCE(rnp->boost_tasks) == NULL)
1003 1004 1005
		return 0;  /* Nothing left to boost. */

	raw_spin_lock_irqsave(&rnp->lock, flags);
1006
	smp_mb__after_unlock_lock();
1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022

	/*
	 * Recheck under the lock: all tasks in need of boosting
	 * might exit their RCU read-side critical sections on their own.
	 */
	if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
		return 0;
	}

	/*
	 * Preferentially boost tasks blocking expedited grace periods.
	 * This cannot starve the normal grace periods because a second
	 * expedited grace period must boost all blocked tasks, including
	 * those blocking the pre-existing normal grace period.
	 */
1023
	if (rnp->exp_tasks != NULL) {
1024
		tb = rnp->exp_tasks;
1025 1026
		rnp->n_exp_boosts++;
	} else {
1027
		tb = rnp->boost_tasks;
1028 1029 1030
		rnp->n_normal_boosts++;
	}
	rnp->n_tasks_boosted++;
1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048

	/*
	 * We boost task t by manufacturing an rt_mutex that appears to
	 * be held by task t.  We leave a pointer to that rt_mutex where
	 * task t can find it, and task t will release the mutex when it
	 * exits its outermost RCU read-side critical section.  Then
	 * simply acquiring this artificial rt_mutex will boost task
	 * t's priority.  (Thanks to tglx for suggesting this approach!)
	 *
	 * Note that task t must acquire rnp->lock to remove itself from
	 * the ->blkd_tasks list, which it will do from exit() if from
	 * nowhere else.  We therefore are guaranteed that task t will
	 * stay around at least until we drop rnp->lock.  Note that
	 * rnp->lock also resolves races between our priority boosting
	 * and task t's exiting its outermost RCU read-side critical
	 * section.
	 */
	t = container_of(tb, struct task_struct, rcu_node_entry);
1049
	rt_mutex_init_proxy_locked(&rnp->boost_mtx, t);
1050
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
1051 1052 1053
	/* Lock only for side effect: boosts task t's priority. */
	rt_mutex_lock(&rnp->boost_mtx);
	rt_mutex_unlock(&rnp->boost_mtx);  /* Then keep lockdep happy. */
1054

1055 1056
	return ACCESS_ONCE(rnp->exp_tasks) != NULL ||
	       ACCESS_ONCE(rnp->boost_tasks) != NULL;
1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068
}

/*
 * Priority-boosting kthread.  One per leaf rcu_node and one for the
 * root rcu_node.
 */
static int rcu_boost_kthread(void *arg)
{
	struct rcu_node *rnp = (struct rcu_node *)arg;
	int spincnt = 0;
	int more2boost;

1069
	trace_rcu_utilization(TPS("Start boost kthread@init"));
1070
	for (;;) {
1071
		rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
1072
		trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
1073
		rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
1074
		trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
1075
		rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
1076 1077 1078 1079 1080 1081
		more2boost = rcu_boost(rnp);
		if (more2boost)
			spincnt++;
		else
			spincnt = 0;
		if (spincnt > 10) {
T
Thomas Gleixner 已提交
1082
			rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
1083
			trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
T
Thomas Gleixner 已提交
1084
			schedule_timeout_interruptible(2);
1085
			trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
1086 1087 1088
			spincnt = 0;
		}
	}
1089
	/* NOTREACHED */
1090
	trace_rcu_utilization(TPS("End boost kthread@notreached"));
1091 1092 1093 1094 1095 1096 1097 1098 1099
	return 0;
}

/*
 * Check to see if it is time to start boosting RCU readers that are
 * blocking the current grace period, and, if so, tell the per-rcu_node
 * kthread to start boosting them.  If there is an expedited grace
 * period in progress, it is always time to boost.
 *
1100 1101 1102
 * The caller must hold rnp->lock, which this function releases.
 * The ->boost_kthread_task is immortal, so we don't need to worry
 * about it going away.
1103
 */
1104
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1105
	__releases(rnp->lock)
1106 1107 1108
{
	struct task_struct *t;

1109 1110
	if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
		rnp->n_balk_exp_gp_tasks++;
1111
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
1112
		return;
1113
	}
1114 1115 1116 1117 1118 1119 1120
	if (rnp->exp_tasks != NULL ||
	    (rnp->gp_tasks != NULL &&
	     rnp->boost_tasks == NULL &&
	     rnp->qsmask == 0 &&
	     ULONG_CMP_GE(jiffies, rnp->boost_time))) {
		if (rnp->exp_tasks == NULL)
			rnp->boost_tasks = rnp->gp_tasks;
1121
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
1122
		t = rnp->boost_kthread_task;
T
Thomas Gleixner 已提交
1123 1124
		if (t)
			rcu_wake_cond(t, rnp->boost_kthread_status);
1125
	} else {
1126
		rcu_initiate_boost_trace(rnp);
1127 1128
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
	}
1129 1130
}

1131 1132 1133 1134 1135 1136 1137 1138 1139
/*
 * Wake up the per-CPU kthread to invoke RCU callbacks.
 */
static void invoke_rcu_callbacks_kthread(void)
{
	unsigned long flags;

	local_irq_save(flags);
	__this_cpu_write(rcu_cpu_has_work, 1);
1140
	if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
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1141 1142 1143 1144
	    current != __this_cpu_read(rcu_cpu_kthread_task)) {
		rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task),
			      __this_cpu_read(rcu_cpu_kthread_status));
	}
1145 1146 1147
	local_irq_restore(flags);
}

1148 1149 1150 1151 1152 1153
/*
 * Is the current CPU running the RCU-callbacks kthread?
 * Caller must have preemption disabled.
 */
static bool rcu_is_callbacks_kthread(void)
{
1154
	return __this_cpu_read(rcu_cpu_kthread_task) == current;
1155 1156
}

1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171
#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)

/*
 * Do priority-boost accounting for the start of a new grace period.
 */
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
{
	rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
}

/*
 * Create an RCU-boost kthread for the specified node if one does not
 * already exist.  We only create this kthread for preemptible RCU.
 * Returns zero if all is well, a negated errno otherwise.
 */
1172
static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
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1173
						 struct rcu_node *rnp)
1174
{
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	int rnp_index = rnp - &rsp->node[0];
1176 1177 1178 1179 1180 1181
	unsigned long flags;
	struct sched_param sp;
	struct task_struct *t;

	if (&rcu_preempt_state != rsp)
		return 0;
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1182 1183 1184 1185

	if (!rcu_scheduler_fully_active || rnp->qsmaskinit == 0)
		return 0;

1186
	rsp->boost = 1;
1187 1188 1189
	if (rnp->boost_kthread_task != NULL)
		return 0;
	t = kthread_create(rcu_boost_kthread, (void *)rnp,
1190
			   "rcub/%d", rnp_index);
1191 1192 1193
	if (IS_ERR(t))
		return PTR_ERR(t);
	raw_spin_lock_irqsave(&rnp->lock, flags);
1194
	smp_mb__after_unlock_lock();
1195 1196
	rnp->boost_kthread_task = t;
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
1197
	sp.sched_priority = kthread_prio;
1198
	sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
1199
	wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
1200 1201 1202
	return 0;
}

1203 1204
static void rcu_kthread_do_work(void)
{
1205 1206
	rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data));
	rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&rcu_bh_data));
1207 1208 1209
	rcu_preempt_do_callbacks();
}

1210
static void rcu_cpu_kthread_setup(unsigned int cpu)
1211 1212 1213
{
	struct sched_param sp;

1214
	sp.sched_priority = kthread_prio;
1215
	sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
1216 1217
}

1218
static void rcu_cpu_kthread_park(unsigned int cpu)
1219
{
1220
	per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
1221 1222
}

1223
static int rcu_cpu_kthread_should_run(unsigned int cpu)
1224
{
1225
	return __this_cpu_read(rcu_cpu_has_work);
1226 1227 1228 1229
}

/*
 * Per-CPU kernel thread that invokes RCU callbacks.  This replaces the
1230 1231
 * RCU softirq used in flavors and configurations of RCU that do not
 * support RCU priority boosting.
1232
 */
1233
static void rcu_cpu_kthread(unsigned int cpu)
1234
{
1235 1236
	unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status);
	char work, *workp = this_cpu_ptr(&rcu_cpu_has_work);
1237
	int spincnt;
1238

1239
	for (spincnt = 0; spincnt < 10; spincnt++) {
1240
		trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
1241 1242
		local_bh_disable();
		*statusp = RCU_KTHREAD_RUNNING;
1243 1244
		this_cpu_inc(rcu_cpu_kthread_loops);
		local_irq_disable();
1245 1246
		work = *workp;
		*workp = 0;
1247
		local_irq_enable();
1248 1249 1250
		if (work)
			rcu_kthread_do_work();
		local_bh_enable();
1251
		if (*workp == 0) {
1252
			trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
1253 1254
			*statusp = RCU_KTHREAD_WAITING;
			return;
1255 1256
		}
	}
1257
	*statusp = RCU_KTHREAD_YIELDING;
1258
	trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
1259
	schedule_timeout_interruptible(2);
1260
	trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
1261
	*statusp = RCU_KTHREAD_WAITING;
1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272
}

/*
 * Set the per-rcu_node kthread's affinity to cover all CPUs that are
 * served by the rcu_node in question.  The CPU hotplug lock is still
 * held, so the value of rnp->qsmaskinit will be stable.
 *
 * We don't include outgoingcpu in the affinity set, use -1 if there is
 * no outgoing CPU.  If there are no CPUs left in the affinity set,
 * this function allows the kthread to execute on any CPU.
 */
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static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1274
{
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1275 1276
	struct task_struct *t = rnp->boost_kthread_task;
	unsigned long mask = rnp->qsmaskinit;
1277 1278 1279
	cpumask_var_t cm;
	int cpu;

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1280
	if (!t)
1281
		return;
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1282
	if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
1283 1284 1285 1286
		return;
	for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1)
		if ((mask & 0x1) && cpu != outgoingcpu)
			cpumask_set_cpu(cpu, cm);
1287
	if (cpumask_weight(cm) == 0)
1288
		cpumask_setall(cm);
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1289
	set_cpus_allowed_ptr(t, cm);
1290 1291 1292
	free_cpumask_var(cm);
}

1293 1294 1295 1296 1297 1298 1299 1300
static struct smp_hotplug_thread rcu_cpu_thread_spec = {
	.store			= &rcu_cpu_kthread_task,
	.thread_should_run	= rcu_cpu_kthread_should_run,
	.thread_fn		= rcu_cpu_kthread,
	.thread_comm		= "rcuc/%u",
	.setup			= rcu_cpu_kthread_setup,
	.park			= rcu_cpu_kthread_park,
};
1301 1302

/*
1303
 * Spawn boost kthreads -- called as soon as the scheduler is running.
1304
 */
1305
static void __init rcu_spawn_boost_kthreads(void)
1306 1307
{
	struct rcu_node *rnp;
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	int cpu;
1309

1310
	for_each_possible_cpu(cpu)
1311
		per_cpu(rcu_cpu_has_work, cpu) = 0;
1312
	BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
1313 1314
	rcu_for_each_leaf_node(rcu_state_p, rnp)
		(void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
1315 1316
}

1317
static void rcu_prepare_kthreads(int cpu)
1318
{
1319
	struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
1320 1321 1322
	struct rcu_node *rnp = rdp->mynode;

	/* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
1323
	if (rcu_scheduler_fully_active)
1324
		(void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
1325 1326
}

1327 1328
#else /* #ifdef CONFIG_RCU_BOOST */

1329
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1330
	__releases(rnp->lock)
1331
{
1332
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
1333 1334
}

1335
static void invoke_rcu_callbacks_kthread(void)
1336
{
1337
	WARN_ON_ONCE(1);
1338 1339
}

1340 1341 1342 1343 1344
static bool rcu_is_callbacks_kthread(void)
{
	return false;
}

1345 1346 1347 1348
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
{
}

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static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1350 1351 1352
{
}

1353
static void __init rcu_spawn_boost_kthreads(void)
1354 1355 1356
{
}

1357
static void rcu_prepare_kthreads(int cpu)
1358 1359 1360
{
}

1361 1362
#endif /* #else #ifdef CONFIG_RCU_BOOST */

1363 1364 1365 1366 1367 1368 1369 1370
#if !defined(CONFIG_RCU_FAST_NO_HZ)

/*
 * Check to see if any future RCU-related work will need to be done
 * by the current CPU, even if none need be done immediately, returning
 * 1 if so.  This function is part of the RCU implementation; it is -not-
 * an exported member of the RCU API.
 *
1371 1372
 * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
 * any flavor of RCU.
1373
 */
1374
#ifndef CONFIG_RCU_NOCB_CPU_ALL
1375
int rcu_needs_cpu(unsigned long *delta_jiffies)
1376
{
1377
	*delta_jiffies = ULONG_MAX;
1378
	return rcu_cpu_has_callbacks(NULL);
1379
}
1380
#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1381 1382 1383 1384 1385

/*
 * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
 * after it.
 */
1386
static void rcu_cleanup_after_idle(void)
1387 1388 1389
{
}

1390
/*
1391
 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
1392 1393
 * is nothing.
 */
1394
static void rcu_prepare_for_idle(void)
1395 1396 1397
{
}

1398 1399 1400 1401 1402 1403 1404 1405
/*
 * Don't bother keeping a running count of the number of RCU callbacks
 * posted because CONFIG_RCU_FAST_NO_HZ=n.
 */
static void rcu_idle_count_callbacks_posted(void)
{
}

1406 1407
#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */

1408 1409 1410 1411 1412 1413 1414 1415 1416 1417 1418 1419 1420 1421 1422
/*
 * This code is invoked when a CPU goes idle, at which point we want
 * to have the CPU do everything required for RCU so that it can enter
 * the energy-efficient dyntick-idle mode.  This is handled by a
 * state machine implemented by rcu_prepare_for_idle() below.
 *
 * The following three proprocessor symbols control this state machine:
 *
 * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
 *	to sleep in dyntick-idle mode with RCU callbacks pending.  This
 *	is sized to be roughly one RCU grace period.  Those energy-efficiency
 *	benchmarkers who might otherwise be tempted to set this to a large
 *	number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
 *	system.  And if you are -that- concerned about energy efficiency,
 *	just power the system down and be done with it!
1423 1424 1425
 * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
 *	permitted to sleep in dyntick-idle mode with only lazy RCU
 *	callbacks pending.  Setting this too high can OOM your system.
1426 1427 1428 1429 1430
 *
 * The values below work well in practice.  If future workloads require
 * adjustment, they can be converted into kernel config parameters, though
 * making the state machine smarter might be a better option.
 */
1431
#define RCU_IDLE_GP_DELAY 4		/* Roughly one grace period. */
1432
#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ)	/* Roughly six seconds. */
1433

1434 1435 1436 1437
static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
module_param(rcu_idle_gp_delay, int, 0644);
static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;
module_param(rcu_idle_lazy_gp_delay, int, 0644);
1438

1439
extern int tick_nohz_active;
1440 1441

/*
1442 1443 1444
 * Try to advance callbacks for all flavors of RCU on the current CPU, but
 * only if it has been awhile since the last time we did so.  Afterwards,
 * if there are any callbacks ready for immediate invocation, return true.
1445
 */
1446
static bool __maybe_unused rcu_try_advance_all_cbs(void)
1447
{
1448 1449
	bool cbs_ready = false;
	struct rcu_data *rdp;
1450
	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
1451 1452
	struct rcu_node *rnp;
	struct rcu_state *rsp;
1453

1454 1455
	/* Exit early if we advanced recently. */
	if (jiffies == rdtp->last_advance_all)
1456
		return false;
1457 1458
	rdtp->last_advance_all = jiffies;

1459 1460 1461
	for_each_rcu_flavor(rsp) {
		rdp = this_cpu_ptr(rsp->rda);
		rnp = rdp->mynode;
1462

1463 1464 1465 1466 1467
		/*
		 * Don't bother checking unless a grace period has
		 * completed since we last checked and there are
		 * callbacks not yet ready to invoke.
		 */
1468 1469
		if ((rdp->completed != rnp->completed ||
		     unlikely(ACCESS_ONCE(rdp->gpwrap))) &&
1470
		    rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL])
1471
			note_gp_changes(rsp, rdp);
1472

1473 1474 1475 1476
		if (cpu_has_callbacks_ready_to_invoke(rdp))
			cbs_ready = true;
	}
	return cbs_ready;
1477 1478
}

1479
/*
1480 1481 1482 1483
 * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
 * to invoke.  If the CPU has callbacks, try to advance them.  Tell the
 * caller to set the timeout based on whether or not there are non-lazy
 * callbacks.
1484
 *
1485
 * The caller must have disabled interrupts.
1486
 */
1487
#ifndef CONFIG_RCU_NOCB_CPU_ALL
1488
int rcu_needs_cpu(unsigned long *dj)
1489
{
1490
	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
1491

1492 1493 1494
	/* Snapshot to detect later posting of non-lazy callback. */
	rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;

1495
	/* If no callbacks, RCU doesn't need the CPU. */
1496
	if (!rcu_cpu_has_callbacks(&rdtp->all_lazy)) {
1497
		*dj = ULONG_MAX;
1498 1499
		return 0;
	}
1500 1501 1502 1503 1504

	/* Attempt to advance callbacks. */
	if (rcu_try_advance_all_cbs()) {
		/* Some ready to invoke, so initiate later invocation. */
		invoke_rcu_core();
1505 1506
		return 1;
	}
1507 1508 1509
	rdtp->last_accelerate = jiffies;

	/* Request timer delay depending on laziness, and round. */
1510
	if (!rdtp->all_lazy) {
1511 1512
		*dj = round_up(rcu_idle_gp_delay + jiffies,
			       rcu_idle_gp_delay) - jiffies;
1513
	} else {
1514
		*dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
1515
	}
1516 1517
	return 0;
}
1518
#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1519

1520
/*
1521 1522 1523 1524 1525 1526
 * Prepare a CPU for idle from an RCU perspective.  The first major task
 * is to sense whether nohz mode has been enabled or disabled via sysfs.
 * The second major task is to check to see if a non-lazy callback has
 * arrived at a CPU that previously had only lazy callbacks.  The third
 * major task is to accelerate (that is, assign grace-period numbers to)
 * any recently arrived callbacks.
1527 1528
 *
 * The caller must have disabled interrupts.
1529
 */
1530
static void rcu_prepare_for_idle(void)
1531
{
1532
#ifndef CONFIG_RCU_NOCB_CPU_ALL
1533
	bool needwake;
1534
	struct rcu_data *rdp;
1535
	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
1536 1537
	struct rcu_node *rnp;
	struct rcu_state *rsp;
1538 1539 1540
	int tne;

	/* Handle nohz enablement switches conservatively. */
1541
	tne = ACCESS_ONCE(tick_nohz_active);
1542
	if (tne != rdtp->tick_nohz_enabled_snap) {
1543
		if (rcu_cpu_has_callbacks(NULL))
1544 1545 1546 1547 1548 1549
			invoke_rcu_core(); /* force nohz to see update. */
		rdtp->tick_nohz_enabled_snap = tne;
		return;
	}
	if (!tne)
		return;
1550

1551
	/* If this is a no-CBs CPU, no callbacks, just return. */
1552
	if (rcu_is_nocb_cpu(smp_processor_id()))
1553 1554
		return;

1555
	/*
1556 1557 1558
	 * If a non-lazy callback arrived at a CPU having only lazy
	 * callbacks, invoke RCU core for the side-effect of recalculating
	 * idle duration on re-entry to idle.
1559
	 */
1560 1561
	if (rdtp->all_lazy &&
	    rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) {
1562 1563
		rdtp->all_lazy = false;
		rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
1564
		invoke_rcu_core();
1565 1566 1567
		return;
	}

1568
	/*
1569 1570
	 * If we have not yet accelerated this jiffy, accelerate all
	 * callbacks on this CPU.
1571
	 */
1572
	if (rdtp->last_accelerate == jiffies)
1573
		return;
1574 1575
	rdtp->last_accelerate = jiffies;
	for_each_rcu_flavor(rsp) {
1576
		rdp = this_cpu_ptr(rsp->rda);
1577 1578 1579 1580
		if (!*rdp->nxttail[RCU_DONE_TAIL])
			continue;
		rnp = rdp->mynode;
		raw_spin_lock(&rnp->lock); /* irqs already disabled. */
1581
		smp_mb__after_unlock_lock();
1582
		needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
1583
		raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
1584 1585
		if (needwake)
			rcu_gp_kthread_wake(rsp);
1586
	}
1587
#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1588
}
1589

1590 1591 1592 1593 1594
/*
 * Clean up for exit from idle.  Attempt to advance callbacks based on
 * any grace periods that elapsed while the CPU was idle, and if any
 * callbacks are now ready to invoke, initiate invocation.
 */
1595
static void rcu_cleanup_after_idle(void)
1596
{
1597
#ifndef CONFIG_RCU_NOCB_CPU_ALL
1598
	if (rcu_is_nocb_cpu(smp_processor_id()))
1599
		return;
1600 1601
	if (rcu_try_advance_all_cbs())
		invoke_rcu_core();
1602
#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1603 1604
}

1605
/*
1606 1607 1608 1609 1610 1611
 * Keep a running count of the number of non-lazy callbacks posted
 * on this CPU.  This running counter (which is never decremented) allows
 * rcu_prepare_for_idle() to detect when something out of the idle loop
 * posts a callback, even if an equal number of callbacks are invoked.
 * Of course, callbacks should only be posted from within a trace event
 * designed to be called from idle or from within RCU_NONIDLE().
1612 1613 1614
 */
static void rcu_idle_count_callbacks_posted(void)
{
1615
	__this_cpu_add(rcu_dynticks.nonlazy_posted, 1);
1616 1617
}

1618 1619 1620 1621 1622 1623 1624 1625 1626 1627 1628 1629 1630 1631 1632 1633 1634 1635 1636 1637 1638 1639 1640 1641 1642 1643 1644 1645 1646
/*
 * Data for flushing lazy RCU callbacks at OOM time.
 */
static atomic_t oom_callback_count;
static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq);

/*
 * RCU OOM callback -- decrement the outstanding count and deliver the
 * wake-up if we are the last one.
 */
static void rcu_oom_callback(struct rcu_head *rhp)
{
	if (atomic_dec_and_test(&oom_callback_count))
		wake_up(&oom_callback_wq);
}

/*
 * Post an rcu_oom_notify callback on the current CPU if it has at
 * least one lazy callback.  This will unnecessarily post callbacks
 * to CPUs that already have a non-lazy callback at the end of their
 * callback list, but this is an infrequent operation, so accept some
 * extra overhead to keep things simple.
 */
static void rcu_oom_notify_cpu(void *unused)
{
	struct rcu_state *rsp;
	struct rcu_data *rdp;

	for_each_rcu_flavor(rsp) {
1647
		rdp = raw_cpu_ptr(rsp->rda);
1648 1649 1650 1651 1652 1653 1654 1655 1656 1657 1658 1659 1660 1661 1662 1663 1664 1665 1666 1667 1668
		if (rdp->qlen_lazy != 0) {
			atomic_inc(&oom_callback_count);
			rsp->call(&rdp->oom_head, rcu_oom_callback);
		}
	}
}

/*
 * If low on memory, ensure that each CPU has a non-lazy callback.
 * This will wake up CPUs that have only lazy callbacks, in turn
 * ensuring that they free up the corresponding memory in a timely manner.
 * Because an uncertain amount of memory will be freed in some uncertain
 * timeframe, we do not claim to have freed anything.
 */
static int rcu_oom_notify(struct notifier_block *self,
			  unsigned long notused, void *nfreed)
{
	int cpu;

	/* Wait for callbacks from earlier instance to complete. */
	wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0);
1669
	smp_mb(); /* Ensure callback reuse happens after callback invocation. */
1670 1671 1672 1673 1674 1675 1676 1677 1678 1679

	/*
	 * Prevent premature wakeup: ensure that all increments happen
	 * before there is a chance of the counter reaching zero.
	 */
	atomic_set(&oom_callback_count, 1);

	get_online_cpus();
	for_each_online_cpu(cpu) {
		smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
1680
		cond_resched_rcu_qs();
1681 1682 1683 1684 1685 1686 1687 1688 1689 1690 1691 1692 1693 1694 1695 1696 1697 1698 1699 1700
	}
	put_online_cpus();

	/* Unconditionally decrement: no need to wake ourselves up. */
	atomic_dec(&oom_callback_count);

	return NOTIFY_OK;
}

static struct notifier_block rcu_oom_nb = {
	.notifier_call = rcu_oom_notify
};

static int __init rcu_register_oom_notifier(void)
{
	register_oom_notifier(&rcu_oom_nb);
	return 0;
}
early_initcall(rcu_register_oom_notifier);

1701
#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1702 1703 1704 1705 1706 1707 1708

#ifdef CONFIG_RCU_CPU_STALL_INFO

#ifdef CONFIG_RCU_FAST_NO_HZ

static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
{
1709
	struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1710
	unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap;
1711

1712 1713 1714 1715 1716
	sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c",
		rdtp->last_accelerate & 0xffff, jiffies & 0xffff,
		ulong2long(nlpd),
		rdtp->all_lazy ? 'L' : '.',
		rdtp->tick_nohz_enabled_snap ? '.' : 'D');
1717 1718 1719 1720 1721 1722
}

#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */

static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
{
1723
	*cp = '\0';
1724 1725 1726 1727 1728 1729 1730
}

#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */

/* Initiate the stall-info list. */
static void print_cpu_stall_info_begin(void)
{
1731
	pr_cont("\n");
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 1757 1758 1759 1760 1761
}

/*
 * Print out diagnostic information for the specified stalled CPU.
 *
 * If the specified CPU is aware of the current RCU grace period
 * (flavor specified by rsp), then print the number of scheduling
 * clock interrupts the CPU has taken during the time that it has
 * been aware.  Otherwise, print the number of RCU grace periods
 * that this CPU is ignorant of, for example, "1" if the CPU was
 * aware of the previous grace period.
 *
 * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
 */
static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
{
	char fast_no_hz[72];
	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
	struct rcu_dynticks *rdtp = rdp->dynticks;
	char *ticks_title;
	unsigned long ticks_value;

	if (rsp->gpnum == rdp->gpnum) {
		ticks_title = "ticks this GP";
		ticks_value = rdp->ticks_this_gp;
	} else {
		ticks_title = "GPs behind";
		ticks_value = rsp->gpnum - rdp->gpnum;
	}
	print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
1762
	pr_err("\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u fqs=%ld %s\n",
1763 1764 1765
	       cpu, ticks_value, ticks_title,
	       atomic_read(&rdtp->dynticks) & 0xfff,
	       rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
1766
	       rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
1767
	       ACCESS_ONCE(rsp->n_force_qs) - rsp->n_force_qs_gpstart,
1768 1769 1770 1771 1772 1773
	       fast_no_hz);
}

/* Terminate the stall-info list. */
static void print_cpu_stall_info_end(void)
{
1774
	pr_err("\t");
1775 1776 1777 1778 1779 1780
}

/* Zero ->ticks_this_gp for all flavors of RCU. */
static void zero_cpu_stall_ticks(struct rcu_data *rdp)
{
	rdp->ticks_this_gp = 0;
1781
	rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
1782 1783 1784 1785 1786
}

/* Increment ->ticks_this_gp for all flavors of RCU. */
static void increment_cpu_stall_ticks(void)
{
1787 1788 1789
	struct rcu_state *rsp;

	for_each_rcu_flavor(rsp)
1790
		raw_cpu_inc(rsp->rda->ticks_this_gp);
1791 1792 1793 1794 1795 1796
}

#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */

static void print_cpu_stall_info_begin(void)
{
1797
	pr_cont(" {");
1798 1799 1800 1801
}

static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
{
1802
	pr_cont(" %d", cpu);
1803 1804 1805 1806
}

static void print_cpu_stall_info_end(void)
{
1807
	pr_cont("} ");
1808 1809 1810 1811 1812 1813 1814 1815 1816 1817 1818
}

static void zero_cpu_stall_ticks(struct rcu_data *rdp)
{
}

static void increment_cpu_stall_ticks(void)
{
}

#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
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#ifdef CONFIG_RCU_NOCB_CPU

/*
 * Offload callback processing from the boot-time-specified set of CPUs
 * specified by rcu_nocb_mask.  For each CPU in the set, there is a
 * kthread created that pulls the callbacks from the corresponding CPU,
 * waits for a grace period to elapse, and invokes the callbacks.
 * The no-CBs CPUs do a wake_up() on their kthread when they insert
 * a callback into any empty list, unless the rcu_nocb_poll boot parameter
 * has been specified, in which case each kthread actively polls its
 * CPU.  (Which isn't so great for energy efficiency, but which does
 * reduce RCU's overhead on that CPU.)
 *
 * This is intended to be used in conjunction with Frederic Weisbecker's
 * adaptive-idle work, which would seriously reduce OS jitter on CPUs
 * running CPU-bound user-mode computations.
 *
 * Offloading of callback processing could also in theory be used as
 * an energy-efficiency measure because CPUs with no RCU callbacks
 * queued are more aggressive about entering dyntick-idle mode.
 */


/* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */
static int __init rcu_nocb_setup(char *str)
{
	alloc_bootmem_cpumask_var(&rcu_nocb_mask);
	have_rcu_nocb_mask = true;
	cpulist_parse(str, rcu_nocb_mask);
	return 1;
}
__setup("rcu_nocbs=", rcu_nocb_setup);

1853 1854 1855 1856 1857 1858 1859
static int __init parse_rcu_nocb_poll(char *arg)
{
	rcu_nocb_poll = 1;
	return 0;
}
early_param("rcu_nocb_poll", parse_rcu_nocb_poll);

1860
/*
1861 1862
 * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
 * grace period.
1863
 */
1864
static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
1865
{
1866
	wake_up_all(&rnp->nocb_gp_wq[rnp->completed & 0x1]);
1867 1868 1869
}

/*
1870
 * Set the root rcu_node structure's ->need_future_gp field
1871 1872 1873 1874 1875
 * based on the sum of those of all rcu_node structures.  This does
 * double-count the root rcu_node structure's requests, but this
 * is necessary to handle the possibility of a rcu_nocb_kthread()
 * having awakened during the time that the rcu_node structures
 * were being updated for the end of the previous grace period.
1876
 */
1877 1878
static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
{
1879
	rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq;
1880 1881 1882
}

static void rcu_init_one_nocb(struct rcu_node *rnp)
1883
{
1884 1885
	init_waitqueue_head(&rnp->nocb_gp_wq[0]);
	init_waitqueue_head(&rnp->nocb_gp_wq[1]);
1886 1887
}

1888
#ifndef CONFIG_RCU_NOCB_CPU_ALL
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1889
/* Is the specified CPU a no-CBs CPU? */
1890
bool rcu_is_nocb_cpu(int cpu)
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{
	if (have_rcu_nocb_mask)
		return cpumask_test_cpu(cpu, rcu_nocb_mask);
	return false;
}
1896
#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
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1898 1899 1900 1901 1902 1903 1904 1905 1906
/*
 * Kick the leader kthread for this NOCB group.
 */
static void wake_nocb_leader(struct rcu_data *rdp, bool force)
{
	struct rcu_data *rdp_leader = rdp->nocb_leader;

	if (!ACCESS_ONCE(rdp_leader->nocb_kthread))
		return;
1907
	if (ACCESS_ONCE(rdp_leader->nocb_leader_sleep) || force) {
1908
		/* Prior smp_mb__after_atomic() orders against prior enqueue. */
1909
		ACCESS_ONCE(rdp_leader->nocb_leader_sleep) = false;
1910 1911 1912 1913
		wake_up(&rdp_leader->nocb_wq);
	}
}

1914 1915 1916 1917 1918 1919 1920
/*
 * Does the specified CPU need an RCU callback for the specified flavor
 * of rcu_barrier()?
 */
static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu)
{
	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
1921 1922
	unsigned long ret;
#ifdef CONFIG_PROVE_RCU
1923
	struct rcu_head *rhp;
1924
#endif /* #ifdef CONFIG_PROVE_RCU */
1925

1926 1927 1928 1929 1930 1931 1932 1933 1934 1935 1936 1937 1938
	/*
	 * Check count of all no-CBs callbacks awaiting invocation.
	 * There needs to be a barrier before this function is called,
	 * but associated with a prior determination that no more
	 * callbacks would be posted.  In the worst case, the first
	 * barrier in _rcu_barrier() suffices (but the caller cannot
	 * necessarily rely on this, not a substitute for the caller
	 * getting the concurrency design right!).  There must also be
	 * a barrier between the following load an posting of a callback
	 * (if a callback is in fact needed).  This is associated with an
	 * atomic_inc() in the caller.
	 */
	ret = atomic_long_read(&rdp->nocb_q_count);
1939

1940
#ifdef CONFIG_PROVE_RCU
1941 1942 1943 1944 1945 1946 1947 1948 1949 1950 1951 1952 1953
	rhp = ACCESS_ONCE(rdp->nocb_head);
	if (!rhp)
		rhp = ACCESS_ONCE(rdp->nocb_gp_head);
	if (!rhp)
		rhp = ACCESS_ONCE(rdp->nocb_follower_head);

	/* Having no rcuo kthread but CBs after scheduler starts is bad! */
	if (!ACCESS_ONCE(rdp->nocb_kthread) && rhp) {
		/* RCU callback enqueued before CPU first came online??? */
		pr_err("RCU: Never-onlined no-CBs CPU %d has CB %p\n",
		       cpu, rhp->func);
		WARN_ON_ONCE(1);
	}
1954
#endif /* #ifdef CONFIG_PROVE_RCU */
1955

1956
	return !!ret;
1957 1958
}

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/*
 * Enqueue the specified string of rcu_head structures onto the specified
 * CPU's no-CBs lists.  The CPU is specified by rdp, the head of the
 * string by rhp, and the tail of the string by rhtp.  The non-lazy/lazy
 * counts are supplied by rhcount and rhcount_lazy.
 *
 * If warranted, also wake up the kthread servicing this CPUs queues.
 */
static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
				    struct rcu_head *rhp,
				    struct rcu_head **rhtp,
1970 1971
				    int rhcount, int rhcount_lazy,
				    unsigned long flags)
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{
	int len;
	struct rcu_head **old_rhpp;
	struct task_struct *t;

	/* Enqueue the callback on the nocb list and update counts. */
1978 1979
	atomic_long_add(rhcount, &rdp->nocb_q_count);
	/* rcu_barrier() relies on ->nocb_q_count add before xchg. */
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	old_rhpp = xchg(&rdp->nocb_tail, rhtp);
	ACCESS_ONCE(*old_rhpp) = rhp;
	atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy);
1983
	smp_mb__after_atomic(); /* Store *old_rhpp before _wake test. */
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	/* If we are not being polled and there is a kthread, awaken it ... */
	t = ACCESS_ONCE(rdp->nocb_kthread);
1987
	if (rcu_nocb_poll || !t) {
1988 1989
		trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
				    TPS("WakeNotPoll"));
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		return;
1991
	}
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	len = atomic_long_read(&rdp->nocb_q_count);
	if (old_rhpp == &rdp->nocb_head) {
1994
		if (!irqs_disabled_flags(flags)) {
1995 1996
			/* ... if queue was empty ... */
			wake_nocb_leader(rdp, false);
1997 1998 1999
			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
					    TPS("WakeEmpty"));
		} else {
2000
			rdp->nocb_defer_wakeup = RCU_NOGP_WAKE;
2001 2002 2003
			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
					    TPS("WakeEmptyIsDeferred"));
		}
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		rdp->qlen_last_fqs_check = 0;
	} else if (len > rdp->qlen_last_fqs_check + qhimark) {
2006
		/* ... or if many callbacks queued. */
2007 2008 2009 2010 2011 2012 2013 2014 2015
		if (!irqs_disabled_flags(flags)) {
			wake_nocb_leader(rdp, true);
			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
					    TPS("WakeOvf"));
		} else {
			rdp->nocb_defer_wakeup = RCU_NOGP_WAKE_FORCE;
			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
					    TPS("WakeOvfIsDeferred"));
		}
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Paul E. McKenney 已提交
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		rdp->qlen_last_fqs_check = LONG_MAX / 2;
2017 2018
	} else {
		trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot"));
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2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032
	}
	return;
}

/*
 * This is a helper for __call_rcu(), which invokes this when the normal
 * callback queue is inoperable.  If this is not a no-CBs CPU, this
 * function returns failure back to __call_rcu(), which can complain
 * appropriately.
 *
 * Otherwise, this function queues the callback where the corresponding
 * "rcuo" kthread can find it.
 */
static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
2033
			    bool lazy, unsigned long flags)
P
Paul E. McKenney 已提交
2034 2035
{

2036
	if (!rcu_is_nocb_cpu(rdp->cpu))
2037
		return false;
2038
	__call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy, flags);
2039 2040 2041
	if (__is_kfree_rcu_offset((unsigned long)rhp->func))
		trace_rcu_kfree_callback(rdp->rsp->name, rhp,
					 (unsigned long)rhp->func,
2042 2043
					 -atomic_long_read(&rdp->nocb_q_count_lazy),
					 -atomic_long_read(&rdp->nocb_q_count));
2044 2045
	else
		trace_rcu_callback(rdp->rsp->name, rhp,
2046 2047
				   -atomic_long_read(&rdp->nocb_q_count_lazy),
				   -atomic_long_read(&rdp->nocb_q_count));
2048 2049 2050 2051 2052 2053 2054 2055 2056 2057 2058

	/*
	 * If called from an extended quiescent state with interrupts
	 * disabled, invoke the RCU core in order to allow the idle-entry
	 * deferred-wakeup check to function.
	 */
	if (irqs_disabled_flags(flags) &&
	    !rcu_is_watching() &&
	    cpu_online(smp_processor_id()))
		invoke_rcu_core();

2059
	return true;
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Paul E. McKenney 已提交
2060 2061 2062 2063 2064 2065 2066
}

/*
 * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is
 * not a no-CBs CPU.
 */
static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
2067 2068
						     struct rcu_data *rdp,
						     unsigned long flags)
P
Paul E. McKenney 已提交
2069 2070 2071 2072 2073
{
	long ql = rsp->qlen;
	long qll = rsp->qlen_lazy;

	/* If this is not a no-CBs CPU, tell the caller to do it the old way. */
2074
	if (!rcu_is_nocb_cpu(smp_processor_id()))
2075
		return false;
P
Paul E. McKenney 已提交
2076 2077 2078 2079 2080 2081
	rsp->qlen = 0;
	rsp->qlen_lazy = 0;

	/* First, enqueue the donelist, if any.  This preserves CB ordering. */
	if (rsp->orphan_donelist != NULL) {
		__call_rcu_nocb_enqueue(rdp, rsp->orphan_donelist,
2082
					rsp->orphan_donetail, ql, qll, flags);
P
Paul E. McKenney 已提交
2083 2084 2085 2086 2087 2088
		ql = qll = 0;
		rsp->orphan_donelist = NULL;
		rsp->orphan_donetail = &rsp->orphan_donelist;
	}
	if (rsp->orphan_nxtlist != NULL) {
		__call_rcu_nocb_enqueue(rdp, rsp->orphan_nxtlist,
2089
					rsp->orphan_nxttail, ql, qll, flags);
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Paul E. McKenney 已提交
2090 2091 2092 2093
		ql = qll = 0;
		rsp->orphan_nxtlist = NULL;
		rsp->orphan_nxttail = &rsp->orphan_nxtlist;
	}
2094
	return true;
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2095 2096 2097
}

/*
2098 2099
 * If necessary, kick off a new grace period, and either way wait
 * for a subsequent grace period to complete.
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2100
 */
2101
static void rcu_nocb_wait_gp(struct rcu_data *rdp)
P
Paul E. McKenney 已提交
2102
{
2103
	unsigned long c;
2104
	bool d;
2105
	unsigned long flags;
2106
	bool needwake;
2107 2108 2109
	struct rcu_node *rnp = rdp->mynode;

	raw_spin_lock_irqsave(&rnp->lock, flags);
2110
	smp_mb__after_unlock_lock();
2111
	needwake = rcu_start_future_gp(rnp, rdp, &c);
2112
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
2113 2114
	if (needwake)
		rcu_gp_kthread_wake(rdp->rsp);
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2115 2116

	/*
2117 2118
	 * Wait for the grace period.  Do so interruptibly to avoid messing
	 * up the load average.
P
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2119
	 */
2120
	trace_rcu_future_gp(rnp, rdp, c, TPS("StartWait"));
2121
	for (;;) {
2122 2123 2124 2125
		wait_event_interruptible(
			rnp->nocb_gp_wq[c & 0x1],
			(d = ULONG_CMP_GE(ACCESS_ONCE(rnp->completed), c)));
		if (likely(d))
2126
			break;
2127
		WARN_ON(signal_pending(current));
2128
		trace_rcu_future_gp(rnp, rdp, c, TPS("ResumeWait"));
2129
	}
2130
	trace_rcu_future_gp(rnp, rdp, c, TPS("EndWait"));
2131
	smp_mb(); /* Ensure that CB invocation happens after GP end. */
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2132 2133
}

2134 2135 2136 2137 2138 2139 2140 2141 2142 2143 2144 2145 2146 2147 2148 2149 2150
/*
 * Leaders come here to wait for additional callbacks to show up.
 * This function does not return until callbacks appear.
 */
static void nocb_leader_wait(struct rcu_data *my_rdp)
{
	bool firsttime = true;
	bool gotcbs;
	struct rcu_data *rdp;
	struct rcu_head **tail;

wait_again:

	/* Wait for callbacks to appear. */
	if (!rcu_nocb_poll) {
		trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, "Sleep");
		wait_event_interruptible(my_rdp->nocb_wq,
2151
				!ACCESS_ONCE(my_rdp->nocb_leader_sleep));
2152 2153 2154 2155 2156 2157 2158 2159 2160 2161 2162 2163 2164 2165 2166 2167 2168 2169 2170 2171 2172 2173 2174 2175 2176 2177 2178 2179 2180 2181 2182
		/* Memory barrier handled by smp_mb() calls below and repoll. */
	} else if (firsttime) {
		firsttime = false; /* Don't drown trace log with "Poll"! */
		trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, "Poll");
	}

	/*
	 * Each pass through the following loop checks a follower for CBs.
	 * We are our own first follower.  Any CBs found are moved to
	 * nocb_gp_head, where they await a grace period.
	 */
	gotcbs = false;
	for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {
		rdp->nocb_gp_head = ACCESS_ONCE(rdp->nocb_head);
		if (!rdp->nocb_gp_head)
			continue;  /* No CBs here, try next follower. */

		/* Move callbacks to wait-for-GP list, which is empty. */
		ACCESS_ONCE(rdp->nocb_head) = NULL;
		rdp->nocb_gp_tail = xchg(&rdp->nocb_tail, &rdp->nocb_head);
		gotcbs = true;
	}

	/*
	 * If there were no callbacks, sleep a bit, rescan after a
	 * memory barrier, and go retry.
	 */
	if (unlikely(!gotcbs)) {
		if (!rcu_nocb_poll)
			trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu,
					    "WokeEmpty");
2183
		WARN_ON(signal_pending(current));
2184 2185 2186
		schedule_timeout_interruptible(1);

		/* Rescan in case we were a victim of memory ordering. */
2187 2188
		my_rdp->nocb_leader_sleep = true;
		smp_mb();  /* Ensure _sleep true before scan. */
2189 2190 2191
		for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower)
			if (ACCESS_ONCE(rdp->nocb_head)) {
				/* Found CB, so short-circuit next wait. */
2192
				my_rdp->nocb_leader_sleep = false;
2193 2194 2195 2196 2197 2198 2199 2200 2201
				break;
			}
		goto wait_again;
	}

	/* Wait for one grace period. */
	rcu_nocb_wait_gp(my_rdp);

	/*
2202 2203
	 * We left ->nocb_leader_sleep unset to reduce cache thrashing.
	 * We set it now, but recheck for new callbacks while
2204 2205
	 * traversing our follower list.
	 */
2206 2207
	my_rdp->nocb_leader_sleep = true;
	smp_mb(); /* Ensure _sleep true before scan of ->nocb_head. */
2208 2209 2210 2211

	/* Each pass through the following loop wakes a follower, if needed. */
	for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {
		if (ACCESS_ONCE(rdp->nocb_head))
2212
			my_rdp->nocb_leader_sleep = false;/* No need to sleep.*/
2213 2214 2215 2216 2217 2218
		if (!rdp->nocb_gp_head)
			continue; /* No CBs, so no need to wake follower. */

		/* Append callbacks to follower's "done" list. */
		tail = xchg(&rdp->nocb_follower_tail, rdp->nocb_gp_tail);
		*tail = rdp->nocb_gp_head;
2219
		smp_mb__after_atomic(); /* Store *tail before wakeup. */
2220 2221 2222 2223 2224 2225 2226 2227 2228 2229 2230 2231 2232 2233 2234 2235 2236 2237 2238 2239 2240 2241 2242 2243 2244 2245 2246 2247 2248 2249 2250 2251 2252 2253 2254 2255 2256 2257 2258 2259
		if (rdp != my_rdp && tail == &rdp->nocb_follower_head) {
			/*
			 * List was empty, wake up the follower.
			 * Memory barriers supplied by atomic_long_add().
			 */
			wake_up(&rdp->nocb_wq);
		}
	}

	/* If we (the leader) don't have CBs, go wait some more. */
	if (!my_rdp->nocb_follower_head)
		goto wait_again;
}

/*
 * Followers come here to wait for additional callbacks to show up.
 * This function does not return until callbacks appear.
 */
static void nocb_follower_wait(struct rcu_data *rdp)
{
	bool firsttime = true;

	for (;;) {
		if (!rcu_nocb_poll) {
			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
					    "FollowerSleep");
			wait_event_interruptible(rdp->nocb_wq,
						 ACCESS_ONCE(rdp->nocb_follower_head));
		} else if (firsttime) {
			/* Don't drown trace log with "Poll"! */
			firsttime = false;
			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, "Poll");
		}
		if (smp_load_acquire(&rdp->nocb_follower_head)) {
			/* ^^^ Ensure CB invocation follows _head test. */
			return;
		}
		if (!rcu_nocb_poll)
			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
					    "WokeEmpty");
2260
		WARN_ON(signal_pending(current));
2261 2262 2263 2264
		schedule_timeout_interruptible(1);
	}
}

P
Paul E. McKenney 已提交
2265 2266
/*
 * Per-rcu_data kthread, but only for no-CBs CPUs.  Each kthread invokes
2267 2268 2269
 * callbacks queued by the corresponding no-CBs CPU, however, there is
 * an optional leader-follower relationship so that the grace-period
 * kthreads don't have to do quite so many wakeups.
P
Paul E. McKenney 已提交
2270 2271 2272 2273 2274 2275 2276 2277 2278 2279 2280
 */
static int rcu_nocb_kthread(void *arg)
{
	int c, cl;
	struct rcu_head *list;
	struct rcu_head *next;
	struct rcu_head **tail;
	struct rcu_data *rdp = arg;

	/* Each pass through this loop invokes one batch of callbacks */
	for (;;) {
2281 2282 2283 2284 2285 2286 2287 2288 2289 2290 2291 2292
		/* Wait for callbacks. */
		if (rdp->nocb_leader == rdp)
			nocb_leader_wait(rdp);
		else
			nocb_follower_wait(rdp);

		/* Pull the ready-to-invoke callbacks onto local list. */
		list = ACCESS_ONCE(rdp->nocb_follower_head);
		BUG_ON(!list);
		trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, "WokeNonEmpty");
		ACCESS_ONCE(rdp->nocb_follower_head) = NULL;
		tail = xchg(&rdp->nocb_follower_tail, &rdp->nocb_follower_head);
P
Paul E. McKenney 已提交
2293 2294

		/* Each pass through the following loop invokes a callback. */
2295 2296 2297
		trace_rcu_batch_start(rdp->rsp->name,
				      atomic_long_read(&rdp->nocb_q_count_lazy),
				      atomic_long_read(&rdp->nocb_q_count), -1);
P
Paul E. McKenney 已提交
2298 2299 2300 2301 2302
		c = cl = 0;
		while (list) {
			next = list->next;
			/* Wait for enqueuing to complete, if needed. */
			while (next == NULL && &list->next != tail) {
2303 2304
				trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
						    TPS("WaitQueue"));
P
Paul E. McKenney 已提交
2305
				schedule_timeout_interruptible(1);
2306 2307
				trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
						    TPS("WokeQueue"));
P
Paul E. McKenney 已提交
2308 2309 2310 2311 2312 2313 2314 2315 2316 2317 2318
				next = list->next;
			}
			debug_rcu_head_unqueue(list);
			local_bh_disable();
			if (__rcu_reclaim(rdp->rsp->name, list))
				cl++;
			c++;
			local_bh_enable();
			list = next;
		}
		trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1);
2319 2320 2321
		smp_mb__before_atomic();  /* _add after CB invocation. */
		atomic_long_add(-c, &rdp->nocb_q_count);
		atomic_long_add(-cl, &rdp->nocb_q_count_lazy);
2322
		rdp->n_nocbs_invoked += c;
P
Paul E. McKenney 已提交
2323 2324 2325 2326
	}
	return 0;
}

2327
/* Is a deferred wakeup of rcu_nocb_kthread() required? */
2328
static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
2329 2330 2331 2332 2333 2334 2335
{
	return ACCESS_ONCE(rdp->nocb_defer_wakeup);
}

/* Do a deferred wakeup of rcu_nocb_kthread(). */
static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
{
2336 2337
	int ndw;

2338 2339
	if (!rcu_nocb_need_deferred_wakeup(rdp))
		return;
2340 2341 2342 2343
	ndw = ACCESS_ONCE(rdp->nocb_defer_wakeup);
	ACCESS_ONCE(rdp->nocb_defer_wakeup) = RCU_NOGP_WAKE_NOT;
	wake_nocb_leader(rdp, ndw == RCU_NOGP_WAKE_FORCE);
	trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("DeferredWake"));
2344 2345
}

2346 2347 2348 2349 2350 2351 2352 2353 2354 2355 2356 2357 2358 2359 2360 2361
void __init rcu_init_nohz(void)
{
	int cpu;
	bool need_rcu_nocb_mask = true;
	struct rcu_state *rsp;

#ifdef CONFIG_RCU_NOCB_CPU_NONE
	need_rcu_nocb_mask = false;
#endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */

#if defined(CONFIG_NO_HZ_FULL)
	if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask))
		need_rcu_nocb_mask = true;
#endif /* #if defined(CONFIG_NO_HZ_FULL) */

	if (!have_rcu_nocb_mask && need_rcu_nocb_mask) {
2362 2363 2364 2365
		if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
			pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
			return;
		}
2366 2367 2368 2369 2370 2371 2372 2373 2374 2375 2376 2377 2378 2379 2380 2381 2382 2383 2384 2385 2386 2387 2388
		have_rcu_nocb_mask = true;
	}
	if (!have_rcu_nocb_mask)
		return;

#ifdef CONFIG_RCU_NOCB_CPU_ZERO
	pr_info("\tOffload RCU callbacks from CPU 0\n");
	cpumask_set_cpu(0, rcu_nocb_mask);
#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */
#ifdef CONFIG_RCU_NOCB_CPU_ALL
	pr_info("\tOffload RCU callbacks from all CPUs\n");
	cpumask_copy(rcu_nocb_mask, cpu_possible_mask);
#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */
#if defined(CONFIG_NO_HZ_FULL)
	if (tick_nohz_full_running)
		cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
#endif /* #if defined(CONFIG_NO_HZ_FULL) */

	if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
		pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n");
		cpumask_and(rcu_nocb_mask, cpu_possible_mask,
			    rcu_nocb_mask);
	}
2389 2390
	pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n",
		cpumask_pr_args(rcu_nocb_mask));
2391 2392 2393 2394 2395 2396 2397 2398 2399 2400 2401 2402 2403 2404 2405 2406
	if (rcu_nocb_poll)
		pr_info("\tPoll for callbacks from no-CBs CPUs.\n");

	for_each_rcu_flavor(rsp) {
		for_each_cpu(cpu, rcu_nocb_mask) {
			struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);

			/*
			 * If there are early callbacks, they will need
			 * to be moved to the nocb lists.
			 */
			WARN_ON_ONCE(rdp->nxttail[RCU_NEXT_TAIL] !=
				     &rdp->nxtlist &&
				     rdp->nxttail[RCU_NEXT_TAIL] != NULL);
			init_nocb_callback_list(rdp);
		}
2407
		rcu_organize_nocb_kthreads(rsp);
2408
	}
2409 2410
}

P
Paul E. McKenney 已提交
2411 2412 2413 2414 2415
/* Initialize per-rcu_data variables for no-CBs CPUs. */
static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
{
	rdp->nocb_tail = &rdp->nocb_head;
	init_waitqueue_head(&rdp->nocb_wq);
2416
	rdp->nocb_follower_tail = &rdp->nocb_follower_head;
P
Paul E. McKenney 已提交
2417 2418
}

2419 2420 2421 2422 2423 2424 2425 2426 2427 2428 2429 2430 2431 2432 2433 2434 2435 2436 2437 2438 2439 2440 2441 2442 2443 2444 2445 2446 2447 2448
/*
 * If the specified CPU is a no-CBs CPU that does not already have its
 * rcuo kthread for the specified RCU flavor, spawn it.  If the CPUs are
 * brought online out of order, this can require re-organizing the
 * leader-follower relationships.
 */
static void rcu_spawn_one_nocb_kthread(struct rcu_state *rsp, int cpu)
{
	struct rcu_data *rdp;
	struct rcu_data *rdp_last;
	struct rcu_data *rdp_old_leader;
	struct rcu_data *rdp_spawn = per_cpu_ptr(rsp->rda, cpu);
	struct task_struct *t;

	/*
	 * If this isn't a no-CBs CPU or if it already has an rcuo kthread,
	 * then nothing to do.
	 */
	if (!rcu_is_nocb_cpu(cpu) || rdp_spawn->nocb_kthread)
		return;

	/* If we didn't spawn the leader first, reorganize! */
	rdp_old_leader = rdp_spawn->nocb_leader;
	if (rdp_old_leader != rdp_spawn && !rdp_old_leader->nocb_kthread) {
		rdp_last = NULL;
		rdp = rdp_old_leader;
		do {
			rdp->nocb_leader = rdp_spawn;
			if (rdp_last && rdp != rdp_spawn)
				rdp_last->nocb_next_follower = rdp;
2449 2450 2451 2452 2453 2454 2455
			if (rdp == rdp_spawn) {
				rdp = rdp->nocb_next_follower;
			} else {
				rdp_last = rdp;
				rdp = rdp->nocb_next_follower;
				rdp_last->nocb_next_follower = NULL;
			}
2456 2457 2458 2459 2460 2461 2462 2463 2464 2465 2466 2467 2468 2469 2470 2471 2472 2473 2474 2475 2476 2477 2478 2479 2480 2481 2482 2483 2484 2485 2486 2487 2488 2489 2490 2491 2492 2493
		} while (rdp);
		rdp_spawn->nocb_next_follower = rdp_old_leader;
	}

	/* Spawn the kthread for this CPU and RCU flavor. */
	t = kthread_run(rcu_nocb_kthread, rdp_spawn,
			"rcuo%c/%d", rsp->abbr, cpu);
	BUG_ON(IS_ERR(t));
	ACCESS_ONCE(rdp_spawn->nocb_kthread) = t;
}

/*
 * If the specified CPU is a no-CBs CPU that does not already have its
 * rcuo kthreads, spawn them.
 */
static void rcu_spawn_all_nocb_kthreads(int cpu)
{
	struct rcu_state *rsp;

	if (rcu_scheduler_fully_active)
		for_each_rcu_flavor(rsp)
			rcu_spawn_one_nocb_kthread(rsp, cpu);
}

/*
 * Once the scheduler is running, spawn rcuo kthreads for all online
 * no-CBs CPUs.  This assumes that the early_initcall()s happen before
 * non-boot CPUs come online -- if this changes, we will need to add
 * some mutual exclusion.
 */
static void __init rcu_spawn_nocb_kthreads(void)
{
	int cpu;

	for_each_online_cpu(cpu)
		rcu_spawn_all_nocb_kthreads(cpu);
}

2494 2495 2496 2497 2498
/* How many follower CPU IDs per leader?  Default of -1 for sqrt(nr_cpu_ids). */
static int rcu_nocb_leader_stride = -1;
module_param(rcu_nocb_leader_stride, int, 0444);

/*
2499
 * Initialize leader-follower relationships for all no-CBs CPU.
2500
 */
2501
static void __init rcu_organize_nocb_kthreads(struct rcu_state *rsp)
P
Paul E. McKenney 已提交
2502 2503
{
	int cpu;
2504 2505
	int ls = rcu_nocb_leader_stride;
	int nl = 0;  /* Next leader. */
P
Paul E. McKenney 已提交
2506
	struct rcu_data *rdp;
2507 2508
	struct rcu_data *rdp_leader = NULL;  /* Suppress misguided gcc warn. */
	struct rcu_data *rdp_prev = NULL;
P
Paul E. McKenney 已提交
2509

2510
	if (!have_rcu_nocb_mask)
P
Paul E. McKenney 已提交
2511
		return;
2512 2513 2514 2515 2516 2517 2518 2519 2520
	if (ls == -1) {
		ls = int_sqrt(nr_cpu_ids);
		rcu_nocb_leader_stride = ls;
	}

	/*
	 * Each pass through this loop sets up one rcu_data structure and
	 * spawns one rcu_nocb_kthread().
	 */
P
Paul E. McKenney 已提交
2521 2522
	for_each_cpu(cpu, rcu_nocb_mask) {
		rdp = per_cpu_ptr(rsp->rda, cpu);
2523 2524 2525 2526 2527 2528 2529 2530 2531 2532 2533
		if (rdp->cpu >= nl) {
			/* New leader, set up for followers & next leader. */
			nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls;
			rdp->nocb_leader = rdp;
			rdp_leader = rdp;
		} else {
			/* Another follower, link to previous leader. */
			rdp->nocb_leader = rdp_leader;
			rdp_prev->nocb_next_follower = rdp;
		}
		rdp_prev = rdp;
P
Paul E. McKenney 已提交
2534 2535 2536 2537
	}
}

/* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
2538
static bool init_nocb_callback_list(struct rcu_data *rdp)
P
Paul E. McKenney 已提交
2539
{
2540
	if (!rcu_is_nocb_cpu(rdp->cpu))
2541
		return false;
2542

P
Paul E. McKenney 已提交
2543
	rdp->nxttail[RCU_NEXT_TAIL] = NULL;
2544
	return true;
P
Paul E. McKenney 已提交
2545 2546
}

2547 2548
#else /* #ifdef CONFIG_RCU_NOCB_CPU */

2549 2550 2551 2552 2553 2554
static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu)
{
	WARN_ON_ONCE(1); /* Should be dead code. */
	return false;
}

2555
static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
P
Paul E. McKenney 已提交
2556 2557 2558
{
}

2559 2560 2561 2562 2563 2564 2565
static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
{
}

static void rcu_init_one_nocb(struct rcu_node *rnp)
{
}
P
Paul E. McKenney 已提交
2566 2567

static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
2568
			    bool lazy, unsigned long flags)
P
Paul E. McKenney 已提交
2569
{
2570
	return false;
P
Paul E. McKenney 已提交
2571 2572 2573
}

static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
2574 2575
						     struct rcu_data *rdp,
						     unsigned long flags)
P
Paul E. McKenney 已提交
2576
{
2577
	return false;
P
Paul E. McKenney 已提交
2578 2579 2580 2581 2582 2583
}

static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
{
}

2584
static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
2585 2586 2587 2588 2589 2590 2591 2592
{
	return false;
}

static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
{
}

2593 2594 2595 2596 2597
static void rcu_spawn_all_nocb_kthreads(int cpu)
{
}

static void __init rcu_spawn_nocb_kthreads(void)
P
Paul E. McKenney 已提交
2598 2599 2600
{
}

2601
static bool init_nocb_callback_list(struct rcu_data *rdp)
P
Paul E. McKenney 已提交
2602
{
2603
	return false;
P
Paul E. McKenney 已提交
2604 2605 2606
}

#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
2607 2608 2609 2610 2611 2612 2613 2614 2615 2616

/*
 * An adaptive-ticks CPU can potentially execute in kernel mode for an
 * arbitrarily long period of time with the scheduling-clock tick turned
 * off.  RCU will be paying attention to this CPU because it is in the
 * kernel, but the CPU cannot be guaranteed to be executing the RCU state
 * machine because the scheduling-clock tick has been disabled.  Therefore,
 * if an adaptive-ticks CPU is failing to respond to the current grace
 * period and has not be idle from an RCU perspective, kick it.
 */
2617
static void __maybe_unused rcu_kick_nohz_cpu(int cpu)
2618 2619 2620 2621 2622 2623
{
#ifdef CONFIG_NO_HZ_FULL
	if (tick_nohz_full_cpu(cpu))
		smp_send_reschedule(cpu);
#endif /* #ifdef CONFIG_NO_HZ_FULL */
}
2624 2625 2626 2627


#ifdef CONFIG_NO_HZ_FULL_SYSIDLE

2628
static int full_sysidle_state;		/* Current system-idle state. */
2629 2630 2631 2632 2633 2634
#define RCU_SYSIDLE_NOT		0	/* Some CPU is not idle. */
#define RCU_SYSIDLE_SHORT	1	/* All CPUs idle for brief period. */
#define RCU_SYSIDLE_LONG	2	/* All CPUs idle for long enough. */
#define RCU_SYSIDLE_FULL	3	/* All CPUs idle, ready for sysidle. */
#define RCU_SYSIDLE_FULL_NOTED	4	/* Actually entered sysidle state. */

2635 2636 2637 2638 2639 2640
/*
 * Invoked to note exit from irq or task transition to idle.  Note that
 * usermode execution does -not- count as idle here!  After all, we want
 * to detect full-system idle states, not RCU quiescent states and grace
 * periods.  The caller must have disabled interrupts.
 */
2641
static void rcu_sysidle_enter(int irq)
2642 2643
{
	unsigned long j;
2644
	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
2645

2646 2647 2648 2649
	/* If there are no nohz_full= CPUs, no need to track this. */
	if (!tick_nohz_full_enabled())
		return;

2650 2651 2652 2653 2654 2655 2656 2657 2658 2659 2660 2661 2662 2663 2664 2665 2666 2667 2668 2669
	/* Adjust nesting, check for fully idle. */
	if (irq) {
		rdtp->dynticks_idle_nesting--;
		WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0);
		if (rdtp->dynticks_idle_nesting != 0)
			return;  /* Still not fully idle. */
	} else {
		if ((rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) ==
		    DYNTICK_TASK_NEST_VALUE) {
			rdtp->dynticks_idle_nesting = 0;
		} else {
			rdtp->dynticks_idle_nesting -= DYNTICK_TASK_NEST_VALUE;
			WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0);
			return;  /* Still not fully idle. */
		}
	}

	/* Record start of fully idle period. */
	j = jiffies;
	ACCESS_ONCE(rdtp->dynticks_idle_jiffies) = j;
2670
	smp_mb__before_atomic();
2671
	atomic_inc(&rdtp->dynticks_idle);
2672
	smp_mb__after_atomic();
2673 2674 2675
	WARN_ON_ONCE(atomic_read(&rdtp->dynticks_idle) & 0x1);
}

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
/*
 * Unconditionally force exit from full system-idle state.  This is
 * invoked when a normal CPU exits idle, but must be called separately
 * for the timekeeping CPU (tick_do_timer_cpu).  The reason for this
 * is that the timekeeping CPU is permitted to take scheduling-clock
 * interrupts while the system is in system-idle state, and of course
 * rcu_sysidle_exit() has no way of distinguishing a scheduling-clock
 * interrupt from any other type of interrupt.
 */
void rcu_sysidle_force_exit(void)
{
	int oldstate = ACCESS_ONCE(full_sysidle_state);
	int newoldstate;

	/*
	 * Each pass through the following loop attempts to exit full
	 * system-idle state.  If contention proves to be a problem,
	 * a trylock-based contention tree could be used here.
	 */
	while (oldstate > RCU_SYSIDLE_SHORT) {
		newoldstate = cmpxchg(&full_sysidle_state,
				      oldstate, RCU_SYSIDLE_NOT);
		if (oldstate == newoldstate &&
		    oldstate == RCU_SYSIDLE_FULL_NOTED) {
			rcu_kick_nohz_cpu(tick_do_timer_cpu);
			return; /* We cleared it, done! */
		}
		oldstate = newoldstate;
	}
	smp_mb(); /* Order initial oldstate fetch vs. later non-idle work. */
}

2708 2709 2710 2711 2712
/*
 * Invoked to note entry to irq or task transition from idle.  Note that
 * usermode execution does -not- count as idle here!  The caller must
 * have disabled interrupts.
 */
2713
static void rcu_sysidle_exit(int irq)
2714
{
2715 2716
	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);

2717 2718 2719 2720
	/* If there are no nohz_full= CPUs, no need to track this. */
	if (!tick_nohz_full_enabled())
		return;

2721 2722 2723 2724 2725 2726 2727 2728 2729 2730 2731 2732 2733 2734 2735 2736 2737 2738 2739 2740 2741 2742
	/* Adjust nesting, check for already non-idle. */
	if (irq) {
		rdtp->dynticks_idle_nesting++;
		WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0);
		if (rdtp->dynticks_idle_nesting != 1)
			return; /* Already non-idle. */
	} else {
		/*
		 * Allow for irq misnesting.  Yes, it really is possible
		 * to enter an irq handler then never leave it, and maybe
		 * also vice versa.  Handle both possibilities.
		 */
		if (rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) {
			rdtp->dynticks_idle_nesting += DYNTICK_TASK_NEST_VALUE;
			WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0);
			return; /* Already non-idle. */
		} else {
			rdtp->dynticks_idle_nesting = DYNTICK_TASK_EXIT_IDLE;
		}
	}

	/* Record end of idle period. */
2743
	smp_mb__before_atomic();
2744
	atomic_inc(&rdtp->dynticks_idle);
2745
	smp_mb__after_atomic();
2746
	WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks_idle) & 0x1));
2747 2748 2749 2750 2751 2752 2753 2754 2755 2756 2757 2758 2759 2760 2761 2762 2763 2764 2765 2766 2767 2768 2769 2770 2771 2772 2773 2774

	/*
	 * If we are the timekeeping CPU, we are permitted to be non-idle
	 * during a system-idle state.  This must be the case, because
	 * the timekeeping CPU has to take scheduling-clock interrupts
	 * during the time that the system is transitioning to full
	 * system-idle state.  This means that the timekeeping CPU must
	 * invoke rcu_sysidle_force_exit() directly if it does anything
	 * more than take a scheduling-clock interrupt.
	 */
	if (smp_processor_id() == tick_do_timer_cpu)
		return;

	/* Update system-idle state: We are clearly no longer fully idle! */
	rcu_sysidle_force_exit();
}

/*
 * Check to see if the current CPU is idle.  Note that usermode execution
 * does not count as idle.  The caller must have disabled interrupts.
 */
static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
				  unsigned long *maxj)
{
	int cur;
	unsigned long j;
	struct rcu_dynticks *rdtp = rdp->dynticks;

2775 2776 2777 2778
	/* If there are no nohz_full= CPUs, don't check system-wide idleness. */
	if (!tick_nohz_full_enabled())
		return;

2779 2780 2781 2782 2783
	/*
	 * If some other CPU has already reported non-idle, if this is
	 * not the flavor of RCU that tracks sysidle state, or if this
	 * is an offline or the timekeeping CPU, nothing to do.
	 */
2784
	if (!*isidle || rdp->rsp != rcu_state_p ||
2785 2786
	    cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu)
		return;
2787 2788
	if (rcu_gp_in_progress(rdp->rsp))
		WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu);
2789 2790 2791 2792 2793 2794 2795 2796 2797 2798 2799 2800 2801 2802 2803 2804 2805 2806 2807 2808 2809

	/* Pick up current idle and NMI-nesting counter and check. */
	cur = atomic_read(&rdtp->dynticks_idle);
	if (cur & 0x1) {
		*isidle = false; /* We are not idle! */
		return;
	}
	smp_mb(); /* Read counters before timestamps. */

	/* Pick up timestamps. */
	j = ACCESS_ONCE(rdtp->dynticks_idle_jiffies);
	/* If this CPU entered idle more recently, update maxj timestamp. */
	if (ULONG_CMP_LT(*maxj, j))
		*maxj = j;
}

/*
 * Is this the flavor of RCU that is handling full-system idle?
 */
static bool is_sysidle_rcu_state(struct rcu_state *rsp)
{
2810
	return rsp == rcu_state_p;
2811 2812 2813 2814 2815 2816 2817 2818 2819 2820 2821 2822 2823 2824 2825 2826 2827 2828 2829 2830 2831 2832 2833 2834 2835 2836 2837 2838 2839 2840 2841 2842 2843 2844 2845 2846 2847 2848 2849 2850 2851 2852 2853 2854 2855 2856 2857 2858 2859 2860 2861 2862 2863 2864 2865 2866 2867 2868 2869 2870 2871 2872 2873 2874 2875 2876
}

/*
 * Return a delay in jiffies based on the number of CPUs, rcu_node
 * leaf fanout, and jiffies tick rate.  The idea is to allow larger
 * systems more time to transition to full-idle state in order to
 * avoid the cache thrashing that otherwise occur on the state variable.
 * Really small systems (less than a couple of tens of CPUs) should
 * instead use a single global atomically incremented counter, and later
 * versions of this will automatically reconfigure themselves accordingly.
 */
static unsigned long rcu_sysidle_delay(void)
{
	if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
		return 0;
	return DIV_ROUND_UP(nr_cpu_ids * HZ, rcu_fanout_leaf * 1000);
}

/*
 * Advance the full-system-idle state.  This is invoked when all of
 * the non-timekeeping CPUs are idle.
 */
static void rcu_sysidle(unsigned long j)
{
	/* Check the current state. */
	switch (ACCESS_ONCE(full_sysidle_state)) {
	case RCU_SYSIDLE_NOT:

		/* First time all are idle, so note a short idle period. */
		ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_SHORT;
		break;

	case RCU_SYSIDLE_SHORT:

		/*
		 * Idle for a bit, time to advance to next state?
		 * cmpxchg failure means race with non-idle, let them win.
		 */
		if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay()))
			(void)cmpxchg(&full_sysidle_state,
				      RCU_SYSIDLE_SHORT, RCU_SYSIDLE_LONG);
		break;

	case RCU_SYSIDLE_LONG:

		/*
		 * Do an additional check pass before advancing to full.
		 * cmpxchg failure means race with non-idle, let them win.
		 */
		if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay()))
			(void)cmpxchg(&full_sysidle_state,
				      RCU_SYSIDLE_LONG, RCU_SYSIDLE_FULL);
		break;

	default:
		break;
	}
}

/*
 * Found a non-idle non-timekeeping CPU, so kick the system-idle state
 * back to the beginning.
 */
static void rcu_sysidle_cancel(void)
{
	smp_mb();
2877 2878
	if (full_sysidle_state > RCU_SYSIDLE_SHORT)
		ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_NOT;
2879 2880 2881 2882 2883 2884 2885 2886 2887
}

/*
 * Update the sysidle state based on the results of a force-quiescent-state
 * scan of the CPUs' dyntick-idle state.
 */
static void rcu_sysidle_report(struct rcu_state *rsp, int isidle,
			       unsigned long maxj, bool gpkt)
{
2888
	if (rsp != rcu_state_p)
2889 2890 2891 2892 2893 2894 2895 2896 2897 2898 2899 2900 2901 2902 2903 2904
		return;  /* Wrong flavor, ignore. */
	if (gpkt && nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
		return;  /* Running state machine from timekeeping CPU. */
	if (isidle)
		rcu_sysidle(maxj);    /* More idle! */
	else
		rcu_sysidle_cancel(); /* Idle is over. */
}

/*
 * Wrapper for rcu_sysidle_report() when called from the grace-period
 * kthread's context.
 */
static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
				  unsigned long maxj)
{
2905 2906 2907 2908
	/* If there are no nohz_full= CPUs, no need to track this. */
	if (!tick_nohz_full_enabled())
		return;

2909 2910 2911 2912 2913 2914 2915 2916 2917 2918 2919 2920 2921 2922 2923 2924 2925 2926 2927 2928 2929 2930 2931 2932 2933 2934
	rcu_sysidle_report(rsp, isidle, maxj, true);
}

/* Callback and function for forcing an RCU grace period. */
struct rcu_sysidle_head {
	struct rcu_head rh;
	int inuse;
};

static void rcu_sysidle_cb(struct rcu_head *rhp)
{
	struct rcu_sysidle_head *rshp;

	/*
	 * The following memory barrier is needed to replace the
	 * memory barriers that would normally be in the memory
	 * allocator.
	 */
	smp_mb();  /* grace period precedes setting inuse. */

	rshp = container_of(rhp, struct rcu_sysidle_head, rh);
	ACCESS_ONCE(rshp->inuse) = 0;
}

/*
 * Check to see if the system is fully idle, other than the timekeeping CPU.
2935 2936
 * The caller must have disabled interrupts.  This is not intended to be
 * called unless tick_nohz_full_enabled().
2937 2938 2939 2940 2941 2942 2943 2944 2945 2946 2947 2948 2949 2950 2951 2952 2953 2954 2955 2956 2957 2958 2959 2960 2961
 */
bool rcu_sys_is_idle(void)
{
	static struct rcu_sysidle_head rsh;
	int rss = ACCESS_ONCE(full_sysidle_state);

	if (WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu))
		return false;

	/* Handle small-system case by doing a full scan of CPUs. */
	if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) {
		int oldrss = rss - 1;

		/*
		 * One pass to advance to each state up to _FULL.
		 * Give up if any pass fails to advance the state.
		 */
		while (rss < RCU_SYSIDLE_FULL && oldrss < rss) {
			int cpu;
			bool isidle = true;
			unsigned long maxj = jiffies - ULONG_MAX / 4;
			struct rcu_data *rdp;

			/* Scan all the CPUs looking for nonidle CPUs. */
			for_each_possible_cpu(cpu) {
2962
				rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
2963 2964 2965 2966
				rcu_sysidle_check_cpu(rdp, &isidle, &maxj);
				if (!isidle)
					break;
			}
2967
			rcu_sysidle_report(rcu_state_p, isidle, maxj, false);
2968 2969 2970 2971 2972 2973 2974 2975 2976 2977 2978 2979 2980 2981 2982 2983 2984 2985 2986 2987 2988 2989 2990 2991 2992 2993
			oldrss = rss;
			rss = ACCESS_ONCE(full_sysidle_state);
		}
	}

	/* If this is the first observation of an idle period, record it. */
	if (rss == RCU_SYSIDLE_FULL) {
		rss = cmpxchg(&full_sysidle_state,
			      RCU_SYSIDLE_FULL, RCU_SYSIDLE_FULL_NOTED);
		return rss == RCU_SYSIDLE_FULL;
	}

	smp_mb(); /* ensure rss load happens before later caller actions. */

	/* If already fully idle, tell the caller (in case of races). */
	if (rss == RCU_SYSIDLE_FULL_NOTED)
		return true;

	/*
	 * If we aren't there yet, and a grace period is not in flight,
	 * initiate a grace period.  Either way, tell the caller that
	 * we are not there yet.  We use an xchg() rather than an assignment
	 * to make up for the memory barriers that would otherwise be
	 * provided by the memory allocator.
	 */
	if (nr_cpu_ids > CONFIG_NO_HZ_FULL_SYSIDLE_SMALL &&
2994
	    !rcu_gp_in_progress(rcu_state_p) &&
2995 2996 2997
	    !rsh.inuse && xchg(&rsh.inuse, 1) == 0)
		call_rcu(&rsh.rh, rcu_sysidle_cb);
	return false;
2998 2999
}

3000 3001 3002 3003 3004 3005 3006 3007 3008 3009
/*
 * Initialize dynticks sysidle state for CPUs coming online.
 */
static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
{
	rdtp->dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE;
}

#else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */

3010
static void rcu_sysidle_enter(int irq)
3011 3012 3013
{
}

3014
static void rcu_sysidle_exit(int irq)
3015 3016 3017
{
}

3018 3019 3020 3021 3022 3023 3024 3025 3026 3027 3028 3029 3030 3031 3032
static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
				  unsigned long *maxj)
{
}

static bool is_sysidle_rcu_state(struct rcu_state *rsp)
{
	return false;
}

static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
				  unsigned long maxj)
{
}

3033 3034 3035 3036 3037
static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
{
}

#endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
3038 3039 3040 3041 3042 3043 3044 3045

/*
 * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the
 * grace-period kthread will do force_quiescent_state() processing?
 * The idea is to avoid waking up RCU core processing on such a
 * CPU unless the grace period has extended for too long.
 *
 * This code relies on the fact that all NO_HZ_FULL CPUs are also
3046
 * CONFIG_RCU_NOCB_CPU CPUs.
3047 3048 3049 3050 3051 3052 3053 3054 3055 3056 3057
 */
static bool rcu_nohz_full_cpu(struct rcu_state *rsp)
{
#ifdef CONFIG_NO_HZ_FULL
	if (tick_nohz_full_cpu(smp_processor_id()) &&
	    (!rcu_gp_in_progress(rsp) ||
	     ULONG_CMP_LT(jiffies, ACCESS_ONCE(rsp->gp_start) + HZ)))
		return 1;
#endif /* #ifdef CONFIG_NO_HZ_FULL */
	return 0;
}
3058 3059 3060 3061 3062 3063 3064

/*
 * Bind the grace-period kthread for the sysidle flavor of RCU to the
 * timekeeping CPU.
 */
static void rcu_bind_gp_kthread(void)
{
3065
	int __maybe_unused cpu;
3066

3067
	if (!tick_nohz_full_enabled())
3068
		return;
3069 3070 3071
#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
	cpu = tick_do_timer_cpu;
	if (cpu >= 0 && cpu < nr_cpu_ids && raw_smp_processor_id() != cpu)
3072
		set_cpus_allowed_ptr(current, cpumask_of(cpu));
3073 3074 3075 3076
#else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
	if (!is_housekeeping_cpu(raw_smp_processor_id()))
		housekeeping_affine(current);
#endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
3077
}
3078 3079 3080 3081 3082 3083 3084 3085 3086 3087 3088 3089 3090 3091 3092 3093

/* Record the current task on dyntick-idle entry. */
static void rcu_dynticks_task_enter(void)
{
#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
	ACCESS_ONCE(current->rcu_tasks_idle_cpu) = smp_processor_id();
#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
}

/* Record no current task on dyntick-idle exit. */
static void rcu_dynticks_task_exit(void)
{
#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
	ACCESS_ONCE(current->rcu_tasks_idle_cpu) = -1;
#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
}