rcutree_plugin.h 66.2 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
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *
 * 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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#define RCU_KTHREAD_PRIO 1

#ifdef CONFIG_RCU_BOOST
#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
#else
#define RCU_BOOST_PRIO RCU_KTHREAD_PRIO
#endif

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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
	printk(KERN_INFO "\tRCU debugfs-based tracing is enabled.\n");
#endif
#if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32)
	printk(KERN_INFO "\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
	       CONFIG_RCU_FANOUT);
#endif
#ifdef CONFIG_RCU_FANOUT_EXACT
	printk(KERN_INFO "\tHierarchical RCU autobalancing is disabled.\n");
#endif
#ifdef CONFIG_RCU_FAST_NO_HZ
	printk(KERN_INFO
	       "\tRCU dyntick-idle grace-period acceleration is enabled.\n");
#endif
#ifdef CONFIG_PROVE_RCU
	printk(KERN_INFO "\tRCU lockdep checking is enabled.\n");
#endif
#ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE
	printk(KERN_INFO "\tRCU torture testing starts during boot.\n");
#endif
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#if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE)
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	printk(KERN_INFO "\tDump stacks of tasks blocking RCU-preempt GP.\n");
#endif
#if defined(CONFIG_RCU_CPU_STALL_INFO)
	printk(KERN_INFO "\tAdditional per-CPU info printed with stalls.\n");
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#endif
#if NUM_RCU_LVL_4 != 0
	printk(KERN_INFO "\tExperimental four-level hierarchy is enabled.\n");
#endif
}

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#ifdef CONFIG_TREE_PREEMPT_RCU

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struct rcu_state rcu_preempt_state = RCU_STATE_INITIALIZER(rcu_preempt);
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DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data);
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static struct rcu_state *rcu_state = &rcu_preempt_state;
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static void rcu_read_unlock_special(struct task_struct *t);
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static int rcu_preempted_readers_exp(struct rcu_node *rnp);

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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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	printk(KERN_INFO "Preemptible hierarchical RCU implementation.\n");
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	rcu_bootup_announce_oddness();
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}

/*
 * Return the number of RCU-preempt batches processed thus far
 * for debug and statistics.
 */
long rcu_batches_completed_preempt(void)
{
	return rcu_preempt_state.completed;
}
EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt);

/*
 * Return the number of RCU batches processed thus far for debug & stats.
 */
long rcu_batches_completed(void)
{
	return rcu_batches_completed_preempt();
}
EXPORT_SYMBOL_GPL(rcu_batches_completed);

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/*
 * Force a quiescent state for preemptible RCU.
 */
void rcu_force_quiescent_state(void)
{
	force_quiescent_state(&rcu_preempt_state, 0);
}
EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);

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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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 *
 * Unlike the other rcu_*_qs() functions, callers to this function
 * must disable irqs in order to protect the assignment to
 * ->rcu_read_unlock_special.
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 */
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static void rcu_preempt_qs(int cpu)
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{
	struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
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	rdp->passed_quiesce_gpnum = rdp->gpnum;
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	barrier();
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	if (rdp->passed_quiesce == 0)
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		trace_rcu_grace_period("rcu_preempt", rdp->gpnum, "cpuqs");
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	rdp->passed_quiesce = 1;
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	current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
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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(int cpu)
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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 & RCU_READ_UNLOCK_BLOCKED) == 0) {

		/* Possibly blocking in an RCU read-side critical section. */
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		rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu);
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		rnp = rdp->mynode;
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		raw_spin_lock_irqsave(&rnp->lock, flags);
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		t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
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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 &&
		   t->rcu_read_unlock_special) {

		/*
		 * 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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	local_irq_save(flags);
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	rcu_preempt_qs(cpu);
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	local_irq_restore(flags);
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}

/*
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 * Tree-preemptible RCU implementation for rcu_read_lock().
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 * Just increment ->rcu_read_lock_nesting, shared state will be updated
 * if we block.
 */
void __rcu_read_lock(void)
{
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	current->rcu_read_lock_nesting++;
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	barrier();  /* needed if we ever invoke rcu_read_lock in rcutree.c */
}
EXPORT_SYMBOL_GPL(__rcu_read_lock);

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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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	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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/*
 * 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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static noinline void rcu_read_unlock_special(struct task_struct *t)
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{
	int empty;
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	int empty_exp;
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	int 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
	struct rt_mutex *rbmp = NULL;
#endif /* #ifdef CONFIG_RCU_BOOST */
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	struct rcu_node *rnp;
	int special;

	/* 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,
	 * let it know that we have done so.
	 */
	special = t->rcu_read_unlock_special;
	if (special & RCU_READ_UNLOCK_NEED_QS) {
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		rcu_preempt_qs(smp_processor_id());
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	}

	/* Hardware IRQ handlers cannot block. */
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	if (in_irq() || in_serving_softirq()) {
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		local_irq_restore(flags);
		return;
	}

	/* Clean up if blocked during RCU read-side critical section. */
	if (special & RCU_READ_UNLOCK_BLOCKED) {
		t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;

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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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			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_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("rcu_preempt",
						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/clear ->rcu_boost_mutex with rcu_node lock held. */
		if (t->rcu_boost_mutex) {
			rbmp = t->rcu_boost_mutex;
			t->rcu_boost_mutex = NULL;
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		}
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#endif /* #ifdef CONFIG_RCU_BOOST */
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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 && !rcu_preempt_blocked_readers_cgp(rnp)) {
			trace_rcu_quiescent_state_report("preempt_rcu",
							 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
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
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#ifdef CONFIG_RCU_BOOST
		/* Unboost if we were boosted. */
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		if (rbmp)
			rt_mutex_unlock(rbmp);
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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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 * Tree-preemptible RCU implementation for rcu_read_unlock().
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 * Decrement ->rcu_read_lock_nesting.  If the result is zero (outermost
 * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
 * invoke rcu_read_unlock_special() to clean up after a context switch
 * in an RCU read-side critical section and other special cases.
 */
void __rcu_read_unlock(void)
{
	struct task_struct *t = current;

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	if (t->rcu_read_lock_nesting != 1)
		--t->rcu_read_lock_nesting;
	else {
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		barrier();  /* critical section before exit code. */
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		t->rcu_read_lock_nesting = INT_MIN;
		barrier();  /* assign before ->rcu_read_unlock_special load */
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		if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
			rcu_read_unlock_special(t);
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		barrier();  /* ->rcu_read_unlock_special load before assign */
		t->rcu_read_lock_nesting = 0;
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	}
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#ifdef CONFIG_PROVE_LOCKING
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	{
		int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting);

		WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
	}
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#endif /* #ifdef CONFIG_PROVE_LOCKING */
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}
EXPORT_SYMBOL_GPL(__rcu_read_unlock);

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#ifdef CONFIG_RCU_CPU_STALL_VERBOSE

/*
 * 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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	if (!rcu_preempt_blocked_readers_cgp(rnp))
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		return;
	raw_spin_lock_irqsave(&rnp->lock, flags);
	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);
}

#else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */

static void rcu_print_detail_task_stall(struct rcu_state *rsp)
{
}

#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */

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#ifdef CONFIG_RCU_CPU_STALL_INFO

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

static void rcu_print_task_stall_end(void)
{
	printk(KERN_CONT "\n");
}

#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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		printk(KERN_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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/*
 * Suppress preemptible RCU's CPU stall warnings by pushing the
 * time of the next stall-warning message comfortably far into the
 * future.
 */
static void rcu_preempt_stall_reset(void)
{
	rcu_preempt_state.jiffies_stall = jiffies + ULONG_MAX / 2;
}

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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 (!list_empty(&rnp->blkd_tasks))
		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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/*
 * Handle tasklist migration for case in which all CPUs covered by the
 * specified rcu_node have gone offline.  Move them up to the root
 * rcu_node.  The reason for not just moving them to the immediate
 * parent is to remove the need for rcu_read_unlock_special() to
 * make more than two attempts to acquire the target rcu_node's lock.
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 * Returns true if there were tasks blocking the current RCU grace
 * period.
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 *
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 * Returns 1 if there was previously a task blocking the current grace
 * period on the specified rcu_node structure.
 *
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 * The caller must hold rnp->lock with irqs disabled.
 */
586 587 588
static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
				     struct rcu_node *rnp,
				     struct rcu_data *rdp)
589 590 591
{
	struct list_head *lp;
	struct list_head *lp_root;
592
	int retval = 0;
593
	struct rcu_node *rnp_root = rcu_get_root(rsp);
594
	struct task_struct *t;
595

596 597
	if (rnp == rnp_root) {
		WARN_ONCE(1, "Last CPU thought to be offlined?");
598
		return 0;  /* Shouldn't happen: at least one CPU online. */
599
	}
600 601 602

	/* If we are on an internal node, complain bitterly. */
	WARN_ON_ONCE(rnp != rdp->mynode);
603 604

	/*
605 606 607 608 609 610 611
	 * Move tasks up to root rcu_node.  Don't try to get fancy for
	 * this corner-case operation -- just put this node's tasks
	 * at the head of the root node's list, and update the root node's
	 * ->gp_tasks and ->exp_tasks pointers to those of this node's,
	 * if non-NULL.  This might result in waiting for more tasks than
	 * absolutely necessary, but this is a good performance/complexity
	 * tradeoff.
612
	 */
613
	if (rcu_preempt_blocked_readers_cgp(rnp))
614 615 616
		retval |= RCU_OFL_TASKS_NORM_GP;
	if (rcu_preempted_readers_exp(rnp))
		retval |= RCU_OFL_TASKS_EXP_GP;
617 618 619 620 621 622 623 624 625 626 627 628
	lp = &rnp->blkd_tasks;
	lp_root = &rnp_root->blkd_tasks;
	while (!list_empty(lp)) {
		t = list_entry(lp->next, typeof(*t), rcu_node_entry);
		raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
		list_del(&t->rcu_node_entry);
		t->rcu_blocked_node = rnp_root;
		list_add(&t->rcu_node_entry, lp_root);
		if (&t->rcu_node_entry == rnp->gp_tasks)
			rnp_root->gp_tasks = rnp->gp_tasks;
		if (&t->rcu_node_entry == rnp->exp_tasks)
			rnp_root->exp_tasks = rnp->exp_tasks;
629 630 631 632
#ifdef CONFIG_RCU_BOOST
		if (&t->rcu_node_entry == rnp->boost_tasks)
			rnp_root->boost_tasks = rnp->boost_tasks;
#endif /* #ifdef CONFIG_RCU_BOOST */
633
		raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
634
	}
635 636 637 638 639 640 641 642 643 644

#ifdef CONFIG_RCU_BOOST
	/* In case root is being boosted and leaf is not. */
	raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
	if (rnp_root->boost_tasks != NULL &&
	    rnp_root->boost_tasks != rnp_root->gp_tasks)
		rnp_root->boost_tasks = rnp_root->gp_tasks;
	raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
#endif /* #ifdef CONFIG_RCU_BOOST */

645 646
	rnp->gp_tasks = NULL;
	rnp->exp_tasks = NULL;
647
	return retval;
648 649
}

650 651
#endif /* #ifdef CONFIG_HOTPLUG_CPU */

652
/*
P
Paul E. McKenney 已提交
653
 * Do CPU-offline processing for preemptible RCU.
654
 */
655
static void rcu_preempt_cleanup_dead_cpu(int cpu)
656
{
657
	rcu_cleanup_dead_cpu(cpu, &rcu_preempt_state);
658 659
}

660 661 662 663 664 665 666 667 668 669 670 671
/*
 * 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.
 */
static void rcu_preempt_check_callbacks(int cpu)
{
	struct task_struct *t = current;

	if (t->rcu_read_lock_nesting == 0) {
672
		rcu_preempt_qs(cpu);
673 674
		return;
	}
675 676
	if (t->rcu_read_lock_nesting > 0 &&
	    per_cpu(rcu_preempt_data, cpu).qs_pending)
677
		t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
678 679 680
}

/*
P
Paul E. McKenney 已提交
681
 * Process callbacks for preemptible RCU.
682 683 684 685 686 687 688
 */
static void rcu_preempt_process_callbacks(void)
{
	__rcu_process_callbacks(&rcu_preempt_state,
				&__get_cpu_var(rcu_preempt_data));
}

689 690
#ifdef CONFIG_RCU_BOOST

691 692 693 694 695
static void rcu_preempt_do_callbacks(void)
{
	rcu_do_batch(&rcu_preempt_state, &__get_cpu_var(rcu_preempt_data));
}

696 697
#endif /* #ifdef CONFIG_RCU_BOOST */

698
/*
P
Paul E. McKenney 已提交
699
 * Queue a preemptible-RCU callback for invocation after a grace period.
700 701 702
 */
void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
{
703
	__call_rcu(head, func, &rcu_preempt_state, 0);
704 705 706
}
EXPORT_SYMBOL_GPL(call_rcu);

707 708 709 710 711 712 713 714 715 716 717 718 719 720
/*
 * Queue an RCU callback for lazy invocation after a grace period.
 * This will likely be later named something like "call_rcu_lazy()",
 * but this change will require some way of tagging the lazy RCU
 * callbacks in the list of pending callbacks.  Until then, this
 * function may only be called from __kfree_rcu().
 */
void kfree_call_rcu(struct rcu_head *head,
		    void (*func)(struct rcu_head *rcu))
{
	__call_rcu(head, func, &rcu_preempt_state, 1);
}
EXPORT_SYMBOL_GPL(kfree_call_rcu);

721 722 723 724 725
/**
 * 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
726 727 728 729 730
 * 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.
731 732 733
 */
void synchronize_rcu(void)
{
734 735 736 737
	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");
738 739
	if (!rcu_scheduler_active)
		return;
740
	wait_rcu_gp(call_rcu);
741 742 743
}
EXPORT_SYMBOL_GPL(synchronize_rcu);

744 745 746 747 748 749 750 751 752 753 754 755
static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
static long sync_rcu_preempt_exp_count;
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)
{
756
	return rnp->exp_tasks != NULL;
757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781
}

/*
 * 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!)
 *
782 783 784
 * Most callers will set the "wake" flag, but the task initiating the
 * expedited grace period need not wake itself.
 *
785 786
 * Caller must hold sync_rcu_preempt_exp_mutex.
 */
787 788
static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
			       bool wake)
789 790 791 792
{
	unsigned long flags;
	unsigned long mask;

P
Paul E. McKenney 已提交
793
	raw_spin_lock_irqsave(&rnp->lock, flags);
794
	for (;;) {
795 796
		if (!sync_rcu_preempt_exp_done(rnp)) {
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
797
			break;
798
		}
799
		if (rnp->parent == NULL) {
800
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
801 802
			if (wake)
				wake_up(&sync_rcu_preempt_exp_wq);
803 804 805
			break;
		}
		mask = rnp->grpmask;
P
Paul E. McKenney 已提交
806
		raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
807
		rnp = rnp->parent;
P
Paul E. McKenney 已提交
808
		raw_spin_lock(&rnp->lock); /* irqs already disabled */
809 810 811 812 813 814 815 816 817 818 819 820 821 822
		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.
 *
 * Caller must hold sync_rcu_preempt_exp_mutex and rsp->onofflock.
 */
static void
sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
{
823
	unsigned long flags;
824
	int must_wait = 0;
825

826 827 828 829
	raw_spin_lock_irqsave(&rnp->lock, flags);
	if (list_empty(&rnp->blkd_tasks))
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
	else {
830
		rnp->exp_tasks = rnp->blkd_tasks.next;
831
		rcu_initiate_boost(rnp, flags);  /* releases rnp->lock */
832 833
		must_wait = 1;
	}
834
	if (!must_wait)
835
		rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */
836 837
}

838
/*
839 840
 * 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
841
 * the ->blkd_tasks lists and wait for this list to drain.
842 843 844
 */
void synchronize_rcu_expedited(void)
{
845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872
	unsigned long flags;
	struct rcu_node *rnp;
	struct rcu_state *rsp = &rcu_preempt_state;
	long snap;
	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. */

	/*
	 * 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)) {
		if (trycount++ < 10)
			udelay(trycount * num_online_cpus());
		else {
			synchronize_rcu();
			return;
		}
		if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0)
			goto mb_ret; /* Others did our work for us. */
	}
	if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0)
		goto unlock_mb_ret; /* Others did our work for us. */

873
	/* force all RCU readers onto ->blkd_tasks lists. */
874 875
	synchronize_sched_expedited();

P
Paul E. McKenney 已提交
876
	raw_spin_lock_irqsave(&rsp->onofflock, flags);
877 878 879

	/* Initialize ->expmask for all non-leaf rcu_node structures. */
	rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) {
P
Paul E. McKenney 已提交
880
		raw_spin_lock(&rnp->lock); /* irqs already disabled. */
881
		rnp->expmask = rnp->qsmaskinit;
P
Paul E. McKenney 已提交
882
		raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
883 884
	}

885
	/* Snapshot current state of ->blkd_tasks lists. */
886 887 888 889 890
	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));

P
Paul E. McKenney 已提交
891
	raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
892

893
	/* Wait for snapshotted ->blkd_tasks lists to drain. */
894 895 896 897 898 899 900 901 902 903 904
	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. */
	ACCESS_ONCE(sync_rcu_preempt_exp_count)++;
unlock_mb_ret:
	mutex_unlock(&sync_rcu_preempt_exp_mutex);
mb_ret:
	smp_mb(); /* ensure subsequent action seen after grace period. */
905 906 907
}
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);

908
/*
P
Paul E. McKenney 已提交
909
 * Check to see if there is any immediate preemptible-RCU-related work
910 911 912 913 914 915 916 917 918
 * to be done.
 */
static int rcu_preempt_pending(int cpu)
{
	return __rcu_pending(&rcu_preempt_state,
			     &per_cpu(rcu_preempt_data, cpu));
}

/*
919
 * Does preemptible RCU have callbacks on this CPU?
920
 */
921
static int rcu_preempt_cpu_has_callbacks(int cpu)
922 923 924 925
{
	return !!per_cpu(rcu_preempt_data, cpu).nxtlist;
}

926 927 928 929 930 931 932 933 934
/**
 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
 */
void rcu_barrier(void)
{
	_rcu_barrier(&rcu_preempt_state, call_rcu);
}
EXPORT_SYMBOL_GPL(rcu_barrier);

935
/*
P
Paul E. McKenney 已提交
936
 * Initialize preemptible RCU's per-CPU data.
937 938 939 940 941 942
 */
static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
{
	rcu_init_percpu_data(cpu, &rcu_preempt_state, 1);
}

943
/*
944 945
 * Move preemptible RCU's callbacks from dying CPU to other online CPU
 * and record a quiescent state.
946
 */
947
static void rcu_preempt_cleanup_dying_cpu(void)
948
{
949
	rcu_cleanup_dying_cpu(&rcu_preempt_state);
950 951
}

952
/*
P
Paul E. McKenney 已提交
953
 * Initialize preemptible RCU's state structures.
954 955 956
 */
static void __init __rcu_init_preempt(void)
{
957
	rcu_init_one(&rcu_preempt_state, &rcu_preempt_data);
958 959
}

960
/*
P
Paul E. McKenney 已提交
961
 * Check for a task exiting while in a preemptible-RCU read-side
962 963 964 965 966 967 968 969 970 971 972
 * 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 (t->rcu_read_lock_nesting == 0)
		return;
	t->rcu_read_lock_nesting = 1;
973
	__rcu_read_unlock();
974 975 976 977
}

#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */

978 979
static struct rcu_state *rcu_state = &rcu_sched_state;

980 981 982
/*
 * Tell them what RCU they are running.
 */
983
static void __init rcu_bootup_announce(void)
984 985
{
	printk(KERN_INFO "Hierarchical RCU implementation.\n");
986
	rcu_bootup_announce_oddness();
987 988 989 990 991 992 993 994 995 996 997
}

/*
 * Return the number of RCU batches processed thus far for debug & stats.
 */
long rcu_batches_completed(void)
{
	return rcu_batches_completed_sched();
}
EXPORT_SYMBOL_GPL(rcu_batches_completed);

998 999 1000 1001 1002 1003 1004 1005 1006 1007
/*
 * Force a quiescent state for RCU, which, because there is no preemptible
 * RCU, becomes the same as rcu-sched.
 */
void rcu_force_quiescent_state(void)
{
	rcu_sched_force_quiescent_state();
}
EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);

1008
/*
P
Paul E. McKenney 已提交
1009
 * Because preemptible RCU does not exist, we never have to check for
1010 1011
 * CPUs being in quiescent states.
 */
1012
static void rcu_preempt_note_context_switch(int cpu)
1013 1014 1015
{
}

1016
/*
P
Paul E. McKenney 已提交
1017
 * Because preemptible RCU does not exist, there are never any preempted
1018 1019
 * RCU readers.
 */
1020
static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
1021 1022 1023 1024
{
	return 0;
}

1025 1026 1027
#ifdef CONFIG_HOTPLUG_CPU

/* Because preemptible RCU does not exist, no quieting of tasks. */
P
Paul E. McKenney 已提交
1028
static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
1029
{
P
Paul E. McKenney 已提交
1030
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
1031 1032 1033 1034
}

#endif /* #ifdef CONFIG_HOTPLUG_CPU */

1035
/*
P
Paul E. McKenney 已提交
1036
 * Because preemptible RCU does not exist, we never have to check for
1037 1038 1039 1040 1041 1042
 * tasks blocked within RCU read-side critical sections.
 */
static void rcu_print_detail_task_stall(struct rcu_state *rsp)
{
}

1043
/*
P
Paul E. McKenney 已提交
1044
 * Because preemptible RCU does not exist, we never have to check for
1045 1046
 * tasks blocked within RCU read-side critical sections.
 */
1047
static int rcu_print_task_stall(struct rcu_node *rnp)
1048
{
1049
	return 0;
1050 1051
}

1052 1053 1054 1055 1056 1057 1058 1059
/*
 * Because preemptible RCU does not exist, there is no need to suppress
 * its CPU stall warnings.
 */
static void rcu_preempt_stall_reset(void)
{
}

1060
/*
P
Paul E. McKenney 已提交
1061
 * Because there is no preemptible RCU, there can be no readers blocked,
1062 1063
 * so there is no need to check for blocked tasks.  So check only for
 * bogus qsmask values.
1064 1065 1066
 */
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
{
1067
	WARN_ON_ONCE(rnp->qsmask);
1068 1069
}

1070 1071
#ifdef CONFIG_HOTPLUG_CPU

1072
/*
P
Paul E. McKenney 已提交
1073
 * Because preemptible RCU does not exist, it never needs to migrate
1074 1075 1076
 * tasks that were blocked within RCU read-side critical sections, and
 * such non-existent tasks cannot possibly have been blocking the current
 * grace period.
1077
 */
1078 1079 1080
static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
				     struct rcu_node *rnp,
				     struct rcu_data *rdp)
1081
{
1082
	return 0;
1083 1084
}

1085 1086
#endif /* #ifdef CONFIG_HOTPLUG_CPU */

1087
/*
P
Paul E. McKenney 已提交
1088
 * Because preemptible RCU does not exist, it never needs CPU-offline
1089 1090
 * processing.
 */
1091
static void rcu_preempt_cleanup_dead_cpu(int cpu)
1092 1093 1094
{
}

1095
/*
P
Paul E. McKenney 已提交
1096
 * Because preemptible RCU does not exist, it never has any callbacks
1097 1098
 * to check.
 */
1099
static void rcu_preempt_check_callbacks(int cpu)
1100 1101 1102 1103
{
}

/*
P
Paul E. McKenney 已提交
1104
 * Because preemptible RCU does not exist, it never has any callbacks
1105 1106
 * to process.
 */
1107
static void rcu_preempt_process_callbacks(void)
1108 1109 1110
{
}

1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126
/*
 * Queue an RCU callback for lazy invocation after a grace period.
 * This will likely be later named something like "call_rcu_lazy()",
 * but this change will require some way of tagging the lazy RCU
 * callbacks in the list of pending callbacks.  Until then, this
 * function may only be called from __kfree_rcu().
 *
 * Because there is no preemptible RCU, we use RCU-sched instead.
 */
void kfree_call_rcu(struct rcu_head *head,
		    void (*func)(struct rcu_head *rcu))
{
	__call_rcu(head, func, &rcu_sched_state, 1);
}
EXPORT_SYMBOL_GPL(kfree_call_rcu);

1127 1128
/*
 * Wait for an rcu-preempt grace period, but make it happen quickly.
P
Paul E. McKenney 已提交
1129
 * But because preemptible RCU does not exist, map to rcu-sched.
1130 1131 1132 1133 1134 1135 1136
 */
void synchronize_rcu_expedited(void)
{
	synchronize_sched_expedited();
}
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);

1137 1138 1139
#ifdef CONFIG_HOTPLUG_CPU

/*
P
Paul E. McKenney 已提交
1140
 * Because preemptible RCU does not exist, there is never any need to
1141 1142 1143
 * report on tasks preempted in RCU read-side critical sections during
 * expedited RCU grace periods.
 */
1144 1145
static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
			       bool wake)
1146 1147 1148 1149 1150
{
}

#endif /* #ifdef CONFIG_HOTPLUG_CPU */

1151
/*
P
Paul E. McKenney 已提交
1152
 * Because preemptible RCU does not exist, it never has any work to do.
1153 1154 1155 1156 1157 1158 1159
 */
static int rcu_preempt_pending(int cpu)
{
	return 0;
}

/*
1160
 * Because preemptible RCU does not exist, it never has callbacks
1161
 */
1162
static int rcu_preempt_cpu_has_callbacks(int cpu)
1163 1164 1165 1166
{
	return 0;
}

1167
/*
P
Paul E. McKenney 已提交
1168
 * Because preemptible RCU does not exist, rcu_barrier() is just
1169 1170 1171 1172 1173 1174 1175 1176
 * another name for rcu_barrier_sched().
 */
void rcu_barrier(void)
{
	rcu_barrier_sched();
}
EXPORT_SYMBOL_GPL(rcu_barrier);

1177
/*
P
Paul E. McKenney 已提交
1178
 * Because preemptible RCU does not exist, there is no per-CPU
1179 1180 1181 1182 1183 1184
 * data to initialize.
 */
static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
{
}

1185
/*
1186
 * Because there is no preemptible RCU, there is no cleanup to do.
1187
 */
1188
static void rcu_preempt_cleanup_dying_cpu(void)
1189 1190 1191
{
}

1192
/*
P
Paul E. McKenney 已提交
1193
 * Because preemptible RCU does not exist, it need not be initialized.
1194 1195 1196 1197 1198
 */
static void __init __rcu_init_preempt(void)
{
}

1199
#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
1200

1201 1202 1203 1204
#ifdef CONFIG_RCU_BOOST

#include "rtmutex_common.h"

1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217
#ifdef CONFIG_RCU_TRACE

static void rcu_initiate_boost_trace(struct rcu_node *rnp)
{
	if (list_empty(&rnp->blkd_tasks))
		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 &&
1218
		 ULONG_CMP_LT(jiffies, rnp->boost_time))
1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231
		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 */

1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 1265 1266
/*
 * 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 rt_mutex mtx;
	struct task_struct *t;
	struct list_head *tb;

	if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL)
		return 0;  /* Nothing left to boost. */

	raw_spin_lock_irqsave(&rnp->lock, flags);

	/*
	 * 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.
	 */
1267
	if (rnp->exp_tasks != NULL) {
1268
		tb = rnp->exp_tasks;
1269 1270
		rnp->n_exp_boosts++;
	} else {
1271
		tb = rnp->boost_tasks;
1272 1273 1274
		rnp->n_normal_boosts++;
	}
	rnp->n_tasks_boosted++;
1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295 1296 1297 1298

	/*
	 * 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);
	rt_mutex_init_proxy_locked(&mtx, t);
	t->rcu_boost_mutex = &mtx;
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
	rt_mutex_lock(&mtx);  /* Side effect: boosts task t's priority. */
	rt_mutex_unlock(&mtx);  /* Keep lockdep happy. */

1299 1300
	return ACCESS_ONCE(rnp->exp_tasks) != NULL ||
	       ACCESS_ONCE(rnp->boost_tasks) != NULL;
1301 1302 1303 1304 1305 1306 1307 1308 1309 1310
}

/*
 * Timer handler to initiate waking up of boost kthreads that
 * have yielded the CPU due to excessive numbers of tasks to
 * boost.  We wake up the per-rcu_node kthread, which in turn
 * will wake up the booster kthread.
 */
static void rcu_boost_kthread_timer(unsigned long arg)
{
1311
	invoke_rcu_node_kthread((struct rcu_node *)arg);
1312 1313 1314 1315 1316 1317 1318 1319 1320 1321 1322 1323
}

/*
 * 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;

1324
	trace_rcu_utilization("Start boost kthread@init");
1325
	for (;;) {
1326
		rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
1327
		trace_rcu_utilization("End boost kthread@rcu_wait");
1328
		rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
1329
		trace_rcu_utilization("Start boost kthread@rcu_wait");
1330
		rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
1331 1332 1333 1334 1335 1336
		more2boost = rcu_boost(rnp);
		if (more2boost)
			spincnt++;
		else
			spincnt = 0;
		if (spincnt > 10) {
1337
			trace_rcu_utilization("End boost kthread@rcu_yield");
1338
			rcu_yield(rcu_boost_kthread_timer, (unsigned long)rnp);
1339
			trace_rcu_utilization("Start boost kthread@rcu_yield");
1340 1341 1342
			spincnt = 0;
		}
	}
1343
	/* NOTREACHED */
1344
	trace_rcu_utilization("End boost kthread@notreached");
1345 1346 1347 1348 1349 1350 1351 1352 1353
	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.
 *
1354 1355 1356
 * The caller must hold rnp->lock, which this function releases,
 * but irqs remain disabled.  The ->boost_kthread_task is immortal,
 * so we don't need to worry about it going away.
1357
 */
1358
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1359 1360 1361
{
	struct task_struct *t;

1362 1363
	if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
		rnp->n_balk_exp_gp_tasks++;
1364
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
1365
		return;
1366
	}
1367 1368 1369 1370 1371 1372 1373
	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;
1374
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
1375 1376 1377
		t = rnp->boost_kthread_task;
		if (t != NULL)
			wake_up_process(t);
1378
	} else {
1379
		rcu_initiate_boost_trace(rnp);
1380 1381
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
	}
1382 1383
}

1384 1385 1386 1387 1388 1389 1390 1391 1392
/*
 * 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);
1393 1394 1395
	if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
	    current != __this_cpu_read(rcu_cpu_kthread_task))
		wake_up_process(__this_cpu_read(rcu_cpu_kthread_task));
1396 1397 1398
	local_irq_restore(flags);
}

1399 1400 1401 1402 1403 1404 1405 1406 1407
/*
 * Is the current CPU running the RCU-callbacks kthread?
 * Caller must have preemption disabled.
 */
static bool rcu_is_callbacks_kthread(void)
{
	return __get_cpu_var(rcu_cpu_kthread_task) == current;
}

1408 1409 1410 1411 1412
/*
 * Set the affinity of the boost kthread.  The CPU-hotplug locks are
 * held, so no one should be messing with the existence of the boost
 * kthread.
 */
1413 1414 1415 1416 1417 1418 1419 1420 1421 1422 1423 1424 1425 1426 1427 1428 1429 1430 1431 1432 1433 1434 1435 1436 1437 1438 1439 1440 1441 1442 1443 1444 1445 1446 1447
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp,
					  cpumask_var_t cm)
{
	struct task_struct *t;

	t = rnp->boost_kthread_task;
	if (t != NULL)
		set_cpus_allowed_ptr(rnp->boost_kthread_task, cm);
}

#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.
 */
static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
						 struct rcu_node *rnp,
						 int rnp_index)
{
	unsigned long flags;
	struct sched_param sp;
	struct task_struct *t;

	if (&rcu_preempt_state != rsp)
		return 0;
1448
	rsp->boost = 1;
1449 1450 1451
	if (rnp->boost_kthread_task != NULL)
		return 0;
	t = kthread_create(rcu_boost_kthread, (void *)rnp,
1452
			   "rcub/%d", rnp_index);
1453 1454 1455 1456 1457
	if (IS_ERR(t))
		return PTR_ERR(t);
	raw_spin_lock_irqsave(&rnp->lock, flags);
	rnp->boost_kthread_task = t;
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
1458
	sp.sched_priority = RCU_BOOST_PRIO;
1459
	sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
1460
	wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
1461 1462 1463
	return 0;
}

1464 1465 1466 1467 1468 1469 1470 1471 1472 1473 1474 1475 1476 1477 1478 1479 1480 1481 1482 1483 1484 1485 1486 1487 1488 1489 1490 1491 1492 1493 1494 1495 1496 1497 1498 1499 1500 1501 1502 1503 1504 1505 1506 1507 1508 1509 1510 1511 1512 1513 1514 1515 1516 1517 1518 1519 1520 1521 1522 1523 1524 1525 1526 1527 1528 1529 1530 1531 1532 1533 1534 1535 1536 1537 1538 1539 1540 1541 1542 1543 1544 1545 1546 1547 1548 1549 1550 1551 1552
#ifdef CONFIG_HOTPLUG_CPU

/*
 * Stop the RCU's per-CPU kthread when its CPU goes offline,.
 */
static void rcu_stop_cpu_kthread(int cpu)
{
	struct task_struct *t;

	/* Stop the CPU's kthread. */
	t = per_cpu(rcu_cpu_kthread_task, cpu);
	if (t != NULL) {
		per_cpu(rcu_cpu_kthread_task, cpu) = NULL;
		kthread_stop(t);
	}
}

#endif /* #ifdef CONFIG_HOTPLUG_CPU */

static void rcu_kthread_do_work(void)
{
	rcu_do_batch(&rcu_sched_state, &__get_cpu_var(rcu_sched_data));
	rcu_do_batch(&rcu_bh_state, &__get_cpu_var(rcu_bh_data));
	rcu_preempt_do_callbacks();
}

/*
 * Wake up the specified per-rcu_node-structure kthread.
 * Because the per-rcu_node kthreads are immortal, we don't need
 * to do anything to keep them alive.
 */
static void invoke_rcu_node_kthread(struct rcu_node *rnp)
{
	struct task_struct *t;

	t = rnp->node_kthread_task;
	if (t != NULL)
		wake_up_process(t);
}

/*
 * Set the specified CPU's kthread to run RT or not, as specified by
 * the to_rt argument.  The CPU-hotplug locks are held, so the task
 * is not going away.
 */
static void rcu_cpu_kthread_setrt(int cpu, int to_rt)
{
	int policy;
	struct sched_param sp;
	struct task_struct *t;

	t = per_cpu(rcu_cpu_kthread_task, cpu);
	if (t == NULL)
		return;
	if (to_rt) {
		policy = SCHED_FIFO;
		sp.sched_priority = RCU_KTHREAD_PRIO;
	} else {
		policy = SCHED_NORMAL;
		sp.sched_priority = 0;
	}
	sched_setscheduler_nocheck(t, policy, &sp);
}

/*
 * Timer handler to initiate the waking up of per-CPU kthreads that
 * have yielded the CPU due to excess numbers of RCU callbacks.
 * We wake up the per-rcu_node kthread, which in turn will wake up
 * the booster kthread.
 */
static void rcu_cpu_kthread_timer(unsigned long arg)
{
	struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, arg);
	struct rcu_node *rnp = rdp->mynode;

	atomic_or(rdp->grpmask, &rnp->wakemask);
	invoke_rcu_node_kthread(rnp);
}

/*
 * Drop to non-real-time priority and yield, but only after posting a
 * timer that will cause us to regain our real-time priority if we
 * remain preempted.  Either way, we restore our real-time priority
 * before returning.
 */
static void rcu_yield(void (*f)(unsigned long), unsigned long arg)
{
	struct sched_param sp;
	struct timer_list yield_timer;
1553
	int prio = current->rt_priority;
1554 1555 1556 1557 1558 1559 1560

	setup_timer_on_stack(&yield_timer, f, arg);
	mod_timer(&yield_timer, jiffies + 2);
	sp.sched_priority = 0;
	sched_setscheduler_nocheck(current, SCHED_NORMAL, &sp);
	set_user_nice(current, 19);
	schedule();
1561 1562
	set_user_nice(current, 0);
	sp.sched_priority = prio;
1563 1564 1565 1566 1567 1568 1569 1570 1571 1572 1573 1574 1575 1576 1577 1578 1579 1580 1581 1582 1583 1584 1585 1586 1587 1588 1589 1590 1591 1592 1593 1594 1595 1596 1597 1598 1599
	sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
	del_timer(&yield_timer);
}

/*
 * Handle cases where the rcu_cpu_kthread() ends up on the wrong CPU.
 * This can happen while the corresponding CPU is either coming online
 * or going offline.  We cannot wait until the CPU is fully online
 * before starting the kthread, because the various notifier functions
 * can wait for RCU grace periods.  So we park rcu_cpu_kthread() until
 * the corresponding CPU is online.
 *
 * Return 1 if the kthread needs to stop, 0 otherwise.
 *
 * Caller must disable bh.  This function can momentarily enable it.
 */
static int rcu_cpu_kthread_should_stop(int cpu)
{
	while (cpu_is_offline(cpu) ||
	       !cpumask_equal(&current->cpus_allowed, cpumask_of(cpu)) ||
	       smp_processor_id() != cpu) {
		if (kthread_should_stop())
			return 1;
		per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
		per_cpu(rcu_cpu_kthread_cpu, cpu) = raw_smp_processor_id();
		local_bh_enable();
		schedule_timeout_uninterruptible(1);
		if (!cpumask_equal(&current->cpus_allowed, cpumask_of(cpu)))
			set_cpus_allowed_ptr(current, cpumask_of(cpu));
		local_bh_disable();
	}
	per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu;
	return 0;
}

/*
 * Per-CPU kernel thread that invokes RCU callbacks.  This replaces the
1600 1601
 * RCU softirq used in flavors and configurations of RCU that do not
 * support RCU priority boosting.
1602 1603 1604 1605 1606 1607 1608 1609 1610 1611
 */
static int rcu_cpu_kthread(void *arg)
{
	int cpu = (int)(long)arg;
	unsigned long flags;
	int spincnt = 0;
	unsigned int *statusp = &per_cpu(rcu_cpu_kthread_status, cpu);
	char work;
	char *workp = &per_cpu(rcu_cpu_has_work, cpu);

1612
	trace_rcu_utilization("Start CPU kthread@init");
1613 1614
	for (;;) {
		*statusp = RCU_KTHREAD_WAITING;
1615
		trace_rcu_utilization("End CPU kthread@rcu_wait");
1616
		rcu_wait(*workp != 0 || kthread_should_stop());
1617
		trace_rcu_utilization("Start CPU kthread@rcu_wait");
1618 1619 1620 1621 1622 1623 1624 1625 1626 1627 1628 1629 1630 1631 1632 1633 1634 1635 1636 1637
		local_bh_disable();
		if (rcu_cpu_kthread_should_stop(cpu)) {
			local_bh_enable();
			break;
		}
		*statusp = RCU_KTHREAD_RUNNING;
		per_cpu(rcu_cpu_kthread_loops, cpu)++;
		local_irq_save(flags);
		work = *workp;
		*workp = 0;
		local_irq_restore(flags);
		if (work)
			rcu_kthread_do_work();
		local_bh_enable();
		if (*workp != 0)
			spincnt++;
		else
			spincnt = 0;
		if (spincnt > 10) {
			*statusp = RCU_KTHREAD_YIELDING;
1638
			trace_rcu_utilization("End CPU kthread@rcu_yield");
1639
			rcu_yield(rcu_cpu_kthread_timer, (unsigned long)cpu);
1640
			trace_rcu_utilization("Start CPU kthread@rcu_yield");
1641 1642 1643 1644
			spincnt = 0;
		}
	}
	*statusp = RCU_KTHREAD_STOPPED;
1645
	trace_rcu_utilization("End CPU kthread@term");
1646 1647 1648 1649 1650 1651 1652 1653 1654 1655 1656 1657 1658 1659 1660 1661 1662 1663 1664 1665 1666 1667 1668 1669 1670 1671 1672 1673 1674
	return 0;
}

/*
 * Spawn a per-CPU kthread, setting up affinity and priority.
 * Because the CPU hotplug lock is held, no other CPU will be attempting
 * to manipulate rcu_cpu_kthread_task.  There might be another CPU
 * attempting to access it during boot, but the locking in kthread_bind()
 * will enforce sufficient ordering.
 *
 * Please note that we cannot simply refuse to wake up the per-CPU
 * kthread because kthreads are created in TASK_UNINTERRUPTIBLE state,
 * which can result in softlockup complaints if the task ends up being
 * idle for more than a couple of minutes.
 *
 * However, please note also that we cannot bind the per-CPU kthread to its
 * CPU until that CPU is fully online.  We also cannot wait until the
 * CPU is fully online before we create its per-CPU kthread, as this would
 * deadlock the system when CPU notifiers tried waiting for grace
 * periods.  So we bind the per-CPU kthread to its CPU only if the CPU
 * is online.  If its CPU is not yet fully online, then the code in
 * rcu_cpu_kthread() will wait until it is fully online, and then do
 * the binding.
 */
static int __cpuinit rcu_spawn_one_cpu_kthread(int cpu)
{
	struct sched_param sp;
	struct task_struct *t;

1675
	if (!rcu_scheduler_fully_active ||
1676 1677
	    per_cpu(rcu_cpu_kthread_task, cpu) != NULL)
		return 0;
E
Eric Dumazet 已提交
1678 1679 1680
	t = kthread_create_on_node(rcu_cpu_kthread,
				   (void *)(long)cpu,
				   cpu_to_node(cpu),
1681
				   "rcuc/%d", cpu);
1682 1683 1684 1685 1686 1687 1688 1689 1690 1691 1692 1693 1694 1695 1696 1697 1698 1699 1700 1701 1702 1703 1704 1705 1706 1707 1708 1709 1710 1711 1712 1713 1714 1715 1716 1717 1718 1719 1720 1721 1722 1723 1724 1725 1726 1727 1728 1729 1730 1731 1732 1733 1734 1735 1736 1737 1738 1739 1740 1741 1742 1743 1744 1745 1746 1747 1748 1749 1750 1751 1752 1753 1754 1755 1756 1757 1758 1759 1760 1761 1762 1763 1764 1765 1766 1767 1768 1769 1770 1771 1772 1773 1774 1775 1776 1777 1778 1779 1780 1781 1782 1783 1784
	if (IS_ERR(t))
		return PTR_ERR(t);
	if (cpu_online(cpu))
		kthread_bind(t, cpu);
	per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu;
	WARN_ON_ONCE(per_cpu(rcu_cpu_kthread_task, cpu) != NULL);
	sp.sched_priority = RCU_KTHREAD_PRIO;
	sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
	per_cpu(rcu_cpu_kthread_task, cpu) = t;
	wake_up_process(t); /* Get to TASK_INTERRUPTIBLE quickly. */
	return 0;
}

/*
 * Per-rcu_node kthread, which is in charge of waking up the per-CPU
 * kthreads when needed.  We ignore requests to wake up kthreads
 * for offline CPUs, which is OK because force_quiescent_state()
 * takes care of this case.
 */
static int rcu_node_kthread(void *arg)
{
	int cpu;
	unsigned long flags;
	unsigned long mask;
	struct rcu_node *rnp = (struct rcu_node *)arg;
	struct sched_param sp;
	struct task_struct *t;

	for (;;) {
		rnp->node_kthread_status = RCU_KTHREAD_WAITING;
		rcu_wait(atomic_read(&rnp->wakemask) != 0);
		rnp->node_kthread_status = RCU_KTHREAD_RUNNING;
		raw_spin_lock_irqsave(&rnp->lock, flags);
		mask = atomic_xchg(&rnp->wakemask, 0);
		rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */
		for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) {
			if ((mask & 0x1) == 0)
				continue;
			preempt_disable();
			t = per_cpu(rcu_cpu_kthread_task, cpu);
			if (!cpu_online(cpu) || t == NULL) {
				preempt_enable();
				continue;
			}
			per_cpu(rcu_cpu_has_work, cpu) = 1;
			sp.sched_priority = RCU_KTHREAD_PRIO;
			sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
			preempt_enable();
		}
	}
	/* NOTREACHED */
	rnp->node_kthread_status = RCU_KTHREAD_STOPPED;
	return 0;
}

/*
 * 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.
 */
static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
{
	cpumask_var_t cm;
	int cpu;
	unsigned long mask = rnp->qsmaskinit;

	if (rnp->node_kthread_task == NULL)
		return;
	if (!alloc_cpumask_var(&cm, GFP_KERNEL))
		return;
	cpumask_clear(cm);
	for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1)
		if ((mask & 0x1) && cpu != outgoingcpu)
			cpumask_set_cpu(cpu, cm);
	if (cpumask_weight(cm) == 0) {
		cpumask_setall(cm);
		for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++)
			cpumask_clear_cpu(cpu, cm);
		WARN_ON_ONCE(cpumask_weight(cm) == 0);
	}
	set_cpus_allowed_ptr(rnp->node_kthread_task, cm);
	rcu_boost_kthread_setaffinity(rnp, cm);
	free_cpumask_var(cm);
}

/*
 * Spawn a per-rcu_node kthread, setting priority and affinity.
 * Called during boot before online/offline can happen, or, if
 * during runtime, with the main CPU-hotplug locks held.  So only
 * one of these can be executing at a time.
 */
static int __cpuinit rcu_spawn_one_node_kthread(struct rcu_state *rsp,
						struct rcu_node *rnp)
{
	unsigned long flags;
	int rnp_index = rnp - &rsp->node[0];
	struct sched_param sp;
	struct task_struct *t;

1785
	if (!rcu_scheduler_fully_active ||
1786 1787 1788 1789
	    rnp->qsmaskinit == 0)
		return 0;
	if (rnp->node_kthread_task == NULL) {
		t = kthread_create(rcu_node_kthread, (void *)rnp,
1790
				   "rcun/%d", rnp_index);
1791 1792 1793 1794 1795 1796 1797 1798 1799 1800 1801 1802 1803 1804 1805 1806 1807 1808 1809 1810
		if (IS_ERR(t))
			return PTR_ERR(t);
		raw_spin_lock_irqsave(&rnp->lock, flags);
		rnp->node_kthread_task = t;
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
		sp.sched_priority = 99;
		sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
		wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
	}
	return rcu_spawn_one_boost_kthread(rsp, rnp, rnp_index);
}

/*
 * Spawn all kthreads -- called as soon as the scheduler is running.
 */
static int __init rcu_spawn_kthreads(void)
{
	int cpu;
	struct rcu_node *rnp;

1811
	rcu_scheduler_fully_active = 1;
1812 1813 1814 1815 1816 1817 1818 1819 1820 1821 1822 1823 1824 1825 1826 1827 1828 1829 1830 1831 1832
	for_each_possible_cpu(cpu) {
		per_cpu(rcu_cpu_has_work, cpu) = 0;
		if (cpu_online(cpu))
			(void)rcu_spawn_one_cpu_kthread(cpu);
	}
	rnp = rcu_get_root(rcu_state);
	(void)rcu_spawn_one_node_kthread(rcu_state, rnp);
	if (NUM_RCU_NODES > 1) {
		rcu_for_each_leaf_node(rcu_state, rnp)
			(void)rcu_spawn_one_node_kthread(rcu_state, rnp);
	}
	return 0;
}
early_initcall(rcu_spawn_kthreads);

static void __cpuinit rcu_prepare_kthreads(int cpu)
{
	struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
	struct rcu_node *rnp = rdp->mynode;

	/* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
1833
	if (rcu_scheduler_fully_active) {
1834 1835 1836 1837 1838 1839
		(void)rcu_spawn_one_cpu_kthread(cpu);
		if (rnp->node_kthread_task == NULL)
			(void)rcu_spawn_one_node_kthread(rcu_state, rnp);
	}
}

1840 1841
#else /* #ifdef CONFIG_RCU_BOOST */

1842
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1843
{
1844
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
1845 1846
}

1847
static void invoke_rcu_callbacks_kthread(void)
1848
{
1849
	WARN_ON_ONCE(1);
1850 1851
}

1852 1853 1854 1855 1856
static bool rcu_is_callbacks_kthread(void)
{
	return false;
}

1857 1858 1859 1860
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
{
}

1861 1862 1863 1864 1865 1866 1867 1868 1869 1870 1871 1872 1873 1874 1875 1876
#ifdef CONFIG_HOTPLUG_CPU

static void rcu_stop_cpu_kthread(int cpu)
{
}

#endif /* #ifdef CONFIG_HOTPLUG_CPU */

static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
{
}

static void rcu_cpu_kthread_setrt(int cpu, int to_rt)
{
}

1877 1878 1879 1880 1881 1882 1883
static int __init rcu_scheduler_really_started(void)
{
	rcu_scheduler_fully_active = 1;
	return 0;
}
early_initcall(rcu_scheduler_really_started);

1884 1885 1886 1887
static void __cpuinit rcu_prepare_kthreads(int cpu)
{
}

1888 1889
#endif /* #else #ifdef CONFIG_RCU_BOOST */

1890 1891 1892 1893 1894 1895 1896 1897
#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.
 *
1898 1899
 * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
 * any flavor of RCU.
1900 1901 1902
 */
int rcu_needs_cpu(int cpu)
{
1903 1904 1905
	return rcu_cpu_has_callbacks(cpu);
}

1906 1907 1908 1909 1910 1911 1912 1913 1914 1915 1916 1917 1918 1919 1920
/*
 * Because we do not have RCU_FAST_NO_HZ, don't bother initializing for it.
 */
static void rcu_prepare_for_idle_init(int cpu)
{
}

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

1921
/*
1922
 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
1923 1924 1925 1926 1927 1928
 * is nothing.
 */
static void rcu_prepare_for_idle(int cpu)
{
}

1929 1930
#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */

1931 1932 1933 1934 1935 1936 1937 1938 1939 1940 1941 1942 1943 1944 1945 1946 1947 1948 1949 1950 1951 1952 1953 1954 1955
/*
 * 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_FLUSHES gives the maximum number of times that we will attempt
 *	to satisfy RCU.  Beyond this point, it is better to incur a periodic
 *	scheduling-clock interrupt than to loop through the state machine
 *	at full power.
 * RCU_IDLE_OPT_FLUSHES gives the number of RCU_IDLE_FLUSHES that are
 *	optional if RCU does not need anything immediately from this
 *	CPU, even if this CPU still has RCU callbacks queued.  The first
 *	times through the state machine are mandatory: we need to give
 *	the state machine a chance to communicate a quiescent state
 *	to the RCU core.
 * 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!
1956 1957 1958
 * 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.
1959 1960 1961 1962 1963 1964 1965
 *
 * 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.
 */
#define RCU_IDLE_FLUSHES 5		/* Number of dyntick-idle tries. */
#define RCU_IDLE_OPT_FLUSHES 3		/* Optional dyntick-idle tries. */
1966
#define RCU_IDLE_GP_DELAY 6		/* Roughly one grace period. */
1967
#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ)	/* Roughly six seconds. */
1968

1969
static DEFINE_PER_CPU(int, rcu_dyntick_drain);
1970
static DEFINE_PER_CPU(unsigned long, rcu_dyntick_holdoff);
1971
static DEFINE_PER_CPU(struct hrtimer, rcu_idle_gp_timer);
1972 1973
static ktime_t rcu_idle_gp_wait;	/* If some non-lazy callbacks. */
static ktime_t rcu_idle_lazy_gp_wait;	/* If only lazy callbacks. */
1974 1975

/*
1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992
 * Allow the CPU to enter dyntick-idle mode if either: (1) There are no
 * callbacks on this CPU, (2) this CPU has not yet attempted to enter
 * dyntick-idle mode, or (3) this CPU is in the process of attempting to
 * enter dyntick-idle mode.  Otherwise, if we have recently tried and failed
 * to enter dyntick-idle mode, we refuse to try to enter it.  After all,
 * it is better to incur scheduling-clock interrupts than to spin
 * continuously for the same time duration!
 */
int rcu_needs_cpu(int cpu)
{
	/* If no callbacks, RCU doesn't need the CPU. */
	if (!rcu_cpu_has_callbacks(cpu))
		return 0;
	/* Otherwise, RCU needs the CPU only if it recently tried and failed. */
	return per_cpu(rcu_dyntick_holdoff, cpu) == jiffies;
}

1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034
/*
 * Does the specified flavor of RCU have non-lazy callbacks pending on
 * the specified CPU?  Both RCU flavor and CPU are specified by the
 * rcu_data structure.
 */
static bool __rcu_cpu_has_nonlazy_callbacks(struct rcu_data *rdp)
{
	return rdp->qlen != rdp->qlen_lazy;
}

#ifdef CONFIG_TREE_PREEMPT_RCU

/*
 * Are there non-lazy RCU-preempt callbacks?  (There cannot be if there
 * is no RCU-preempt in the kernel.)
 */
static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu)
{
	struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);

	return __rcu_cpu_has_nonlazy_callbacks(rdp);
}

#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */

static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu)
{
	return 0;
}

#endif /* else #ifdef CONFIG_TREE_PREEMPT_RCU */

/*
 * Does any flavor of RCU have non-lazy callbacks on the specified CPU?
 */
static bool rcu_cpu_has_nonlazy_callbacks(int cpu)
{
	return __rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_sched_data, cpu)) ||
	       __rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_bh_data, cpu)) ||
	       rcu_preempt_cpu_has_nonlazy_callbacks(cpu);
}

2035 2036 2037 2038 2039 2040 2041 2042 2043 2044 2045 2046 2047 2048 2049 2050 2051 2052 2053 2054 2055 2056 2057 2058 2059 2060 2061
/*
 * Timer handler used to force CPU to start pushing its remaining RCU
 * callbacks in the case where it entered dyntick-idle mode with callbacks
 * pending.  The hander doesn't really need to do anything because the
 * real work is done upon re-entry to idle, or by the next scheduling-clock
 * interrupt should idle not be re-entered.
 */
static enum hrtimer_restart rcu_idle_gp_timer_func(struct hrtimer *hrtp)
{
	trace_rcu_prep_idle("Timer");
	return HRTIMER_NORESTART;
}

/*
 * Initialize the timer used to pull CPUs out of dyntick-idle mode.
 */
static void rcu_prepare_for_idle_init(int cpu)
{
	static int firsttime = 1;
	struct hrtimer *hrtp = &per_cpu(rcu_idle_gp_timer, cpu);

	hrtimer_init(hrtp, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
	hrtp->function = rcu_idle_gp_timer_func;
	if (firsttime) {
		unsigned int upj = jiffies_to_usecs(RCU_IDLE_GP_DELAY);

		rcu_idle_gp_wait = ns_to_ktime(upj * (u64)1000);
2062 2063
		upj = jiffies_to_usecs(RCU_IDLE_LAZY_GP_DELAY);
		rcu_idle_lazy_gp_wait = ns_to_ktime(upj * (u64)1000);
2064 2065 2066 2067 2068 2069 2070 2071 2072 2073 2074 2075 2076 2077
		firsttime = 0;
	}
}

/*
 * Clean up for exit from idle.  Because we are exiting from idle, there
 * is no longer any point to rcu_idle_gp_timer, so cancel it.  This will
 * do nothing if this timer is not active, so just cancel it unconditionally.
 */
static void rcu_cleanup_after_idle(int cpu)
{
	hrtimer_cancel(&per_cpu(rcu_idle_gp_timer, cpu));
}

2078 2079 2080 2081
/*
 * Check to see if any RCU-related work can be done by the current CPU,
 * and if so, schedule a softirq to get it done.  This function is part
 * of the RCU implementation; it is -not- an exported member of the RCU API.
2082
 *
2083 2084 2085 2086 2087 2088
 * The idea is for the current CPU to clear out all work required by the
 * RCU core for the current grace period, so that this CPU can be permitted
 * to enter dyntick-idle mode.  In some cases, it will need to be awakened
 * at the end of the grace period by whatever CPU ends the grace period.
 * This allows CPUs to go dyntick-idle more quickly, and to reduce the
 * number of wakeups by a modest integer factor.
2089 2090 2091
 *
 * Because it is not legal to invoke rcu_process_callbacks() with irqs
 * disabled, we do one pass of force_quiescent_state(), then do a
2092
 * invoke_rcu_core() to cause rcu_process_callbacks() to be invoked
2093
 * later.  The per-cpu rcu_dyntick_drain variable controls the sequencing.
2094 2095
 *
 * The caller must have disabled interrupts.
2096
 */
2097
static void rcu_prepare_for_idle(int cpu)
2098
{
2099
	/*
2100 2101
	 * If there are no callbacks on this CPU, enter dyntick-idle mode.
	 * Also reset state to avoid prejudicing later attempts.
2102
	 */
2103 2104
	if (!rcu_cpu_has_callbacks(cpu)) {
		per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1;
2105
		per_cpu(rcu_dyntick_drain, cpu) = 0;
2106
		trace_rcu_prep_idle("No callbacks");
2107
		return;
2108
	}
2109 2110 2111 2112 2113

	/*
	 * If in holdoff mode, just return.  We will presumably have
	 * refrained from disabling the scheduling-clock tick.
	 */
2114 2115
	if (per_cpu(rcu_dyntick_holdoff, cpu) == jiffies) {
		trace_rcu_prep_idle("In holdoff");
2116
		return;
2117
	}
2118 2119 2120 2121

	/* Check and update the rcu_dyntick_drain sequencing. */
	if (per_cpu(rcu_dyntick_drain, cpu) <= 0) {
		/* First time through, initialize the counter. */
2122 2123 2124
		per_cpu(rcu_dyntick_drain, cpu) = RCU_IDLE_FLUSHES;
	} else if (per_cpu(rcu_dyntick_drain, cpu) <= RCU_IDLE_OPT_FLUSHES &&
		   !rcu_pending(cpu)) {
2125
		/* Can we go dyntick-idle despite still having callbacks? */
2126 2127 2128
		trace_rcu_prep_idle("Dyntick with callbacks");
		per_cpu(rcu_dyntick_drain, cpu) = 0;
		per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1;
2129 2130 2131
		if (rcu_cpu_has_nonlazy_callbacks(cpu))
			hrtimer_start(&per_cpu(rcu_idle_gp_timer, cpu),
				      rcu_idle_gp_wait, HRTIMER_MODE_REL);
2132 2133 2134
		else
			hrtimer_start(&per_cpu(rcu_idle_gp_timer, cpu),
				      rcu_idle_lazy_gp_wait, HRTIMER_MODE_REL);
2135 2136
		return; /* Nothing more to do immediately. */
	} else if (--per_cpu(rcu_dyntick_drain, cpu) <= 0) {
2137
		/* We have hit the limit, so time to give up. */
2138
		per_cpu(rcu_dyntick_holdoff, cpu) = jiffies;
2139
		trace_rcu_prep_idle("Begin holdoff");
2140 2141
		invoke_rcu_core();  /* Force the CPU out of dyntick-idle. */
		return;
2142 2143
	}

2144 2145 2146 2147 2148 2149 2150 2151 2152 2153
	/*
	 * Do one step of pushing the remaining RCU callbacks through
	 * the RCU core state machine.
	 */
#ifdef CONFIG_TREE_PREEMPT_RCU
	if (per_cpu(rcu_preempt_data, cpu).nxtlist) {
		rcu_preempt_qs(cpu);
		force_quiescent_state(&rcu_preempt_state, 0);
	}
#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
2154 2155 2156 2157 2158 2159 2160
	if (per_cpu(rcu_sched_data, cpu).nxtlist) {
		rcu_sched_qs(cpu);
		force_quiescent_state(&rcu_sched_state, 0);
	}
	if (per_cpu(rcu_bh_data, cpu).nxtlist) {
		rcu_bh_qs(cpu);
		force_quiescent_state(&rcu_bh_state, 0);
2161 2162
	}

2163 2164 2165 2166
	/*
	 * If RCU callbacks are still pending, RCU still needs this CPU.
	 * So try forcing the callbacks through the grace period.
	 */
2167
	if (rcu_cpu_has_callbacks(cpu)) {
2168
		trace_rcu_prep_idle("More callbacks");
2169
		invoke_rcu_core();
2170
	} else
2171
		trace_rcu_prep_idle("Callbacks drained");
2172 2173 2174
}

#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
2175 2176 2177 2178 2179 2180 2181 2182 2183 2184 2185 2186 2187 2188 2189 2190 2191 2192 2193 2194 2195 2196 2197 2198 2199 2200 2201 2202 2203 2204 2205 2206 2207 2208 2209 2210 2211 2212 2213 2214 2215 2216 2217 2218 2219 2220 2221 2222 2223 2224 2225 2226 2227 2228 2229 2230 2231 2232 2233 2234 2235 2236 2237 2238 2239 2240 2241 2242 2243 2244 2245 2246 2247 2248 2249 2250 2251 2252 2253 2254 2255 2256 2257 2258 2259 2260 2261 2262 2263 2264 2265 2266 2267 2268 2269 2270 2271 2272 2273 2274 2275 2276 2277 2278 2279 2280 2281 2282 2283 2284 2285 2286 2287 2288

#ifdef CONFIG_RCU_CPU_STALL_INFO

#ifdef CONFIG_RCU_FAST_NO_HZ

static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
{
	struct hrtimer *hrtp = &per_cpu(rcu_idle_gp_timer, cpu);

	sprintf(cp, "drain=%d %c timer=%lld",
		per_cpu(rcu_dyntick_drain, cpu),
		per_cpu(rcu_dyntick_holdoff, cpu) == jiffies ? 'H' : '.',
		hrtimer_active(hrtp)
			? ktime_to_us(hrtimer_get_remaining(hrtp))
			: -1);
}

#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */

static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
{
}

#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */

/* Initiate the stall-info list. */
static void print_cpu_stall_info_begin(void)
{
	printk(KERN_CONT "\n");
}

/*
 * 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);
	printk(KERN_ERR "\t%d: (%lu %s) idle=%03x/%llx/%d %s\n",
	       cpu, ticks_value, ticks_title,
	       atomic_read(&rdtp->dynticks) & 0xfff,
	       rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
	       fast_no_hz);
}

/* Terminate the stall-info list. */
static void print_cpu_stall_info_end(void)
{
	printk(KERN_ERR "\t");
}

/* Zero ->ticks_this_gp for all flavors of RCU. */
static void zero_cpu_stall_ticks(struct rcu_data *rdp)
{
	rdp->ticks_this_gp = 0;
}

/* Increment ->ticks_this_gp for all flavors of RCU. */
static void increment_cpu_stall_ticks(void)
{
	__get_cpu_var(rcu_sched_data).ticks_this_gp++;
	__get_cpu_var(rcu_bh_data).ticks_this_gp++;
#ifdef CONFIG_TREE_PREEMPT_RCU
	__get_cpu_var(rcu_preempt_data).ticks_this_gp++;
#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
}

#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */

static void print_cpu_stall_info_begin(void)
{
	printk(KERN_CONT " {");
}

static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
{
	printk(KERN_CONT " %d", cpu);
}

static void print_cpu_stall_info_end(void)
{
	printk(KERN_CONT "} ");
}

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 */