From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Mon, 25 Jul 2016 19:41:29 +0000 (-0700)
Subject: Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel... 
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=c86ad14d305d2429c3da19462440bac50c183def;p=GitHub%2Fmoto-9609%2Fandroid_kernel_motorola_exynos9610.git

Merge branch 'locking-core-for-linus' of git://git./linux/kernel/git/tip/tip

Pull locking updates from Ingo Molnar:
 "The locking tree was busier in this cycle than the usual pattern - a
  couple of major projects happened to coincide.

  The main changes are:

   - implement the atomic_fetch_{add,sub,and,or,xor}() API natively
     across all SMP architectures (Peter Zijlstra)

   - add atomic_fetch_{inc/dec}() as well, using the generic primitives
     (Davidlohr Bueso)

   - optimize various aspects of rwsems (Jason Low, Davidlohr Bueso,
     Waiman Long)

   - optimize smp_cond_load_acquire() on arm64 and implement LSE based
     atomic{,64}_fetch_{add,sub,and,andnot,or,xor}{,_relaxed,_acquire,_release}()
     on arm64 (Will Deacon)

   - introduce smp_acquire__after_ctrl_dep() and fix various barrier
     mis-uses and bugs (Peter Zijlstra)

   - after discovering ancient spin_unlock_wait() barrier bugs in its
     implementation and usage, strengthen its semantics and update/fix
     usage sites (Peter Zijlstra)

   - optimize mutex_trylock() fastpath (Peter Zijlstra)

   - ... misc fixes and cleanups"

* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (67 commits)
  locking/atomic: Introduce inc/dec variants for the atomic_fetch_$op() API
  locking/barriers, arch/arm64: Implement LDXR+WFE based smp_cond_load_acquire()
  locking/static_keys: Fix non static symbol Sparse warning
  locking/qspinlock: Use __this_cpu_dec() instead of full-blown this_cpu_dec()
  locking/atomic, arch/tile: Fix tilepro build
  locking/atomic, arch/m68k: Remove comment
  locking/atomic, arch/arc: Fix build
  locking/Documentation: Clarify limited control-dependency scope
  locking/atomic, arch/rwsem: Employ atomic_long_fetch_add()
  locking/atomic, arch/qrwlock: Employ atomic_fetch_add_acquire()
  locking/atomic, arch/mips: Convert to _relaxed atomics
  locking/atomic, arch/alpha: Convert to _relaxed atomics
  locking/atomic: Remove the deprecated atomic_{set,clear}_mask() functions
  locking/atomic: Remove linux/atomic.h:atomic_fetch_or()
  locking/atomic: Implement atomic{,64,_long}_fetch_{add,sub,and,andnot,or,xor}{,_relaxed,_acquire,_release}()
  locking/atomic: Fix atomic64_relaxed() bits
  locking/atomic, arch/xtensa: Implement atomic_fetch_{add,sub,and,or,xor}()
  locking/atomic, arch/x86: Implement atomic{,64}_fetch_{add,sub,and,or,xor}()
  locking/atomic, arch/tile: Implement atomic{,64}_fetch_{add,sub,and,or,xor}()
  locking/atomic, arch/sparc: Implement atomic{,64}_fetch_{add,sub,and,or,xor}()
  ...
---

c86ad14d305d2429c3da19462440bac50c183def
diff --cc kernel/rcu/tree_exp.h
index d400434af6b2,000000000000..6d86ab6ec2c9
mode 100644,000000..100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@@ -1,656 -1,0 +1,655 @@@
 +/*
 + * RCU expedited grace periods
 + *
 + * This program is free software; you can redistribute it and/or modify
 + * it under the terms of the GNU General Public License as published by
 + * the Free Software Foundation; either version 2 of the License, or
 + * (at your option) any later version.
 + *
 + * This program is distributed in the hope that it will be useful,
 + * but WITHOUT ANY WARRANTY; without even the implied warranty of
 + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 + * GNU General Public License for more details.
 + *
 + * You should have received a copy of the GNU General Public License
 + * along with this program; if not, you can access it online at
 + * http://www.gnu.org/licenses/gpl-2.0.html.
 + *
 + * Copyright IBM Corporation, 2016
 + *
 + * Authors: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
 + */
 +
 +/* Wrapper functions for expedited grace periods.  */
 +static void rcu_exp_gp_seq_start(struct rcu_state *rsp)
 +{
 +	rcu_seq_start(&rsp->expedited_sequence);
 +}
 +static void rcu_exp_gp_seq_end(struct rcu_state *rsp)
 +{
 +	rcu_seq_end(&rsp->expedited_sequence);
 +	smp_mb(); /* Ensure that consecutive grace periods serialize. */
 +}
 +static unsigned long rcu_exp_gp_seq_snap(struct rcu_state *rsp)
 +{
 +	unsigned long s;
 +
 +	smp_mb(); /* Caller's modifications seen first by other CPUs. */
 +	s = rcu_seq_snap(&rsp->expedited_sequence);
 +	trace_rcu_exp_grace_period(rsp->name, s, TPS("snap"));
 +	return s;
 +}
 +static bool rcu_exp_gp_seq_done(struct rcu_state *rsp, unsigned long s)
 +{
 +	return rcu_seq_done(&rsp->expedited_sequence, s);
 +}
 +
 +/*
 + * Reset the ->expmaskinit values in the rcu_node tree to reflect any
 + * recent CPU-online activity.  Note that these masks are not cleared
 + * when CPUs go offline, so they reflect the union of all CPUs that have
 + * ever been online.  This means that this function normally takes its
 + * no-work-to-do fastpath.
 + */
 +static void sync_exp_reset_tree_hotplug(struct rcu_state *rsp)
 +{
 +	bool done;
 +	unsigned long flags;
 +	unsigned long mask;
 +	unsigned long oldmask;
 +	int ncpus = READ_ONCE(rsp->ncpus);
 +	struct rcu_node *rnp;
 +	struct rcu_node *rnp_up;
 +
 +	/* If no new CPUs onlined since last time, nothing to do. */
 +	if (likely(ncpus == rsp->ncpus_snap))
 +		return;
 +	rsp->ncpus_snap = ncpus;
 +
 +	/*
 +	 * Each pass through the following loop propagates newly onlined
 +	 * CPUs for the current rcu_node structure up the rcu_node tree.
 +	 */
 +	rcu_for_each_leaf_node(rsp, rnp) {
 +		raw_spin_lock_irqsave_rcu_node(rnp, flags);
 +		if (rnp->expmaskinit == rnp->expmaskinitnext) {
 +			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 +			continue;  /* No new CPUs, nothing to do. */
 +		}
 +
 +		/* Update this node's mask, track old value for propagation. */
 +		oldmask = rnp->expmaskinit;
 +		rnp->expmaskinit = rnp->expmaskinitnext;
 +		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 +
 +		/* If was already nonzero, nothing to propagate. */
 +		if (oldmask)
 +			continue;
 +
 +		/* Propagate the new CPU up the tree. */
 +		mask = rnp->grpmask;
 +		rnp_up = rnp->parent;
 +		done = false;
 +		while (rnp_up) {
 +			raw_spin_lock_irqsave_rcu_node(rnp_up, flags);
 +			if (rnp_up->expmaskinit)
 +				done = true;
 +			rnp_up->expmaskinit |= mask;
 +			raw_spin_unlock_irqrestore_rcu_node(rnp_up, flags);
 +			if (done)
 +				break;
 +			mask = rnp_up->grpmask;
 +			rnp_up = rnp_up->parent;
 +		}
 +	}
 +}
 +
 +/*
 + * Reset the ->expmask values in the rcu_node tree in preparation for
 + * a new expedited grace period.
 + */
 +static void __maybe_unused sync_exp_reset_tree(struct rcu_state *rsp)
 +{
 +	unsigned long flags;
 +	struct rcu_node *rnp;
 +
 +	sync_exp_reset_tree_hotplug(rsp);
 +	rcu_for_each_node_breadth_first(rsp, rnp) {
 +		raw_spin_lock_irqsave_rcu_node(rnp, flags);
 +		WARN_ON_ONCE(rnp->expmask);
 +		rnp->expmask = rnp->expmaskinit;
 +		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 +	}
 +}
 +
 +/*
 + * 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 the rcu_state's exp_mutex.
 + */
 +static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
 +{
 +	return rnp->exp_tasks == NULL &&
 +	       READ_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!)
 + *
 + * Caller must hold the rcu_state's exp_mutex and the specified rcu_node
 + * structure's ->lock.
 + */
 +static void __rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
 +				 bool wake, unsigned long flags)
 +	__releases(rnp->lock)
 +{
 +	unsigned long mask;
 +
 +	for (;;) {
 +		if (!sync_rcu_preempt_exp_done(rnp)) {
 +			if (!rnp->expmask)
 +				rcu_initiate_boost(rnp, flags);
 +			else
 +				raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 +			break;
 +		}
 +		if (rnp->parent == NULL) {
 +			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 +			if (wake) {
 +				smp_mb(); /* EGP done before wake_up(). */
 +				swake_up(&rsp->expedited_wq);
 +			}
 +			break;
 +		}
 +		mask = rnp->grpmask;
 +		raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled */
 +		rnp = rnp->parent;
 +		raw_spin_lock_rcu_node(rnp); /* irqs already disabled */
 +		WARN_ON_ONCE(!(rnp->expmask & mask));
 +		rnp->expmask &= ~mask;
 +	}
 +}
 +
 +/*
 + * Report expedited quiescent state for specified node.  This is a
 + * lock-acquisition wrapper function for __rcu_report_exp_rnp().
 + *
 + * Caller must hold the rcu_state's exp_mutex.
 + */
 +static void __maybe_unused rcu_report_exp_rnp(struct rcu_state *rsp,
 +					      struct rcu_node *rnp, bool wake)
 +{
 +	unsigned long flags;
 +
 +	raw_spin_lock_irqsave_rcu_node(rnp, flags);
 +	__rcu_report_exp_rnp(rsp, rnp, wake, flags);
 +}
 +
 +/*
 + * Report expedited quiescent state for multiple CPUs, all covered by the
 + * specified leaf rcu_node structure.  Caller must hold the rcu_state's
 + * exp_mutex.
 + */
 +static void rcu_report_exp_cpu_mult(struct rcu_state *rsp, struct rcu_node *rnp,
 +				    unsigned long mask, bool wake)
 +{
 +	unsigned long flags;
 +
 +	raw_spin_lock_irqsave_rcu_node(rnp, flags);
 +	if (!(rnp->expmask & mask)) {
 +		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 +		return;
 +	}
 +	rnp->expmask &= ~mask;
 +	__rcu_report_exp_rnp(rsp, rnp, wake, flags); /* Releases rnp->lock. */
 +}
 +
 +/*
 + * Report expedited quiescent state for specified rcu_data (CPU).
 + */
 +static void rcu_report_exp_rdp(struct rcu_state *rsp, struct rcu_data *rdp,
 +			       bool wake)
 +{
 +	rcu_report_exp_cpu_mult(rsp, rdp->mynode, rdp->grpmask, wake);
 +}
 +
 +/* Common code for synchronize_{rcu,sched}_expedited() work-done checking. */
 +static bool sync_exp_work_done(struct rcu_state *rsp, atomic_long_t *stat,
 +			       unsigned long s)
 +{
 +	if (rcu_exp_gp_seq_done(rsp, s)) {
 +		trace_rcu_exp_grace_period(rsp->name, s, TPS("done"));
 +		/* Ensure test happens before caller kfree(). */
 +		smp_mb__before_atomic(); /* ^^^ */
 +		atomic_long_inc(stat);
 +		return true;
 +	}
 +	return false;
 +}
 +
 +/*
 + * Funnel-lock acquisition for expedited grace periods.  Returns true
 + * if some other task completed an expedited grace period that this task
 + * can piggy-back on, and with no mutex held.  Otherwise, returns false
 + * with the mutex held, indicating that the caller must actually do the
 + * expedited grace period.
 + */
 +static bool exp_funnel_lock(struct rcu_state *rsp, unsigned long s)
 +{
 +	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, raw_smp_processor_id());
 +	struct rcu_node *rnp = rdp->mynode;
 +	struct rcu_node *rnp_root = rcu_get_root(rsp);
 +
 +	/* Low-contention fastpath. */
 +	if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s) &&
 +	    (rnp == rnp_root ||
 +	     ULONG_CMP_LT(READ_ONCE(rnp_root->exp_seq_rq), s)) &&
- 	    !mutex_is_locked(&rsp->exp_mutex) &&
 +	    mutex_trylock(&rsp->exp_mutex))
 +		goto fastpath;
 +
 +	/*
 +	 * Each pass through the following loop works its way up
 +	 * the rcu_node tree, returning if others have done the work or
 +	 * otherwise falls through to acquire rsp->exp_mutex.  The mapping
 +	 * from CPU to rcu_node structure can be inexact, as it is just
 +	 * promoting locality and is not strictly needed for correctness.
 +	 */
 +	for (; rnp != NULL; rnp = rnp->parent) {
 +		if (sync_exp_work_done(rsp, &rdp->exp_workdone1, s))
 +			return true;
 +
 +		/* Work not done, either wait here or go up. */
 +		spin_lock(&rnp->exp_lock);
 +		if (ULONG_CMP_GE(rnp->exp_seq_rq, s)) {
 +
 +			/* Someone else doing GP, so wait for them. */
 +			spin_unlock(&rnp->exp_lock);
 +			trace_rcu_exp_funnel_lock(rsp->name, rnp->level,
 +						  rnp->grplo, rnp->grphi,
 +						  TPS("wait"));
 +			wait_event(rnp->exp_wq[(s >> 1) & 0x3],
 +				   sync_exp_work_done(rsp,
 +						      &rdp->exp_workdone2, s));
 +			return true;
 +		}
 +		rnp->exp_seq_rq = s; /* Followers can wait on us. */
 +		spin_unlock(&rnp->exp_lock);
 +		trace_rcu_exp_funnel_lock(rsp->name, rnp->level, rnp->grplo,
 +					  rnp->grphi, TPS("nxtlvl"));
 +	}
 +	mutex_lock(&rsp->exp_mutex);
 +fastpath:
 +	if (sync_exp_work_done(rsp, &rdp->exp_workdone3, s)) {
 +		mutex_unlock(&rsp->exp_mutex);
 +		return true;
 +	}
 +	rcu_exp_gp_seq_start(rsp);
 +	trace_rcu_exp_grace_period(rsp->name, s, TPS("start"));
 +	return false;
 +}
 +
 +/* Invoked on each online non-idle CPU for expedited quiescent state. */
 +static void sync_sched_exp_handler(void *data)
 +{
 +	struct rcu_data *rdp;
 +	struct rcu_node *rnp;
 +	struct rcu_state *rsp = data;
 +
 +	rdp = this_cpu_ptr(rsp->rda);
 +	rnp = rdp->mynode;
 +	if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
 +	    __this_cpu_read(rcu_sched_data.cpu_no_qs.b.exp))
 +		return;
 +	if (rcu_is_cpu_rrupt_from_idle()) {
 +		rcu_report_exp_rdp(&rcu_sched_state,
 +				   this_cpu_ptr(&rcu_sched_data), true);
 +		return;
 +	}
 +	__this_cpu_write(rcu_sched_data.cpu_no_qs.b.exp, true);
 +	resched_cpu(smp_processor_id());
 +}
 +
 +/* Send IPI for expedited cleanup if needed at end of CPU-hotplug operation. */
 +static void sync_sched_exp_online_cleanup(int cpu)
 +{
 +	struct rcu_data *rdp;
 +	int ret;
 +	struct rcu_node *rnp;
 +	struct rcu_state *rsp = &rcu_sched_state;
 +
 +	rdp = per_cpu_ptr(rsp->rda, cpu);
 +	rnp = rdp->mynode;
 +	if (!(READ_ONCE(rnp->expmask) & rdp->grpmask))
 +		return;
 +	ret = smp_call_function_single(cpu, sync_sched_exp_handler, rsp, 0);
 +	WARN_ON_ONCE(ret);
 +}
 +
 +/*
 + * Select the nodes that the upcoming expedited grace period needs
 + * to wait for.
 + */
 +static void sync_rcu_exp_select_cpus(struct rcu_state *rsp,
 +				     smp_call_func_t func)
 +{
 +	int cpu;
 +	unsigned long flags;
 +	unsigned long mask_ofl_test;
 +	unsigned long mask_ofl_ipi;
 +	int ret;
 +	struct rcu_node *rnp;
 +
 +	sync_exp_reset_tree(rsp);
 +	rcu_for_each_leaf_node(rsp, rnp) {
 +		raw_spin_lock_irqsave_rcu_node(rnp, flags);
 +
 +		/* Each pass checks a CPU for identity, offline, and idle. */
 +		mask_ofl_test = 0;
 +		for_each_leaf_node_possible_cpu(rnp, cpu) {
 +			struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
 +			struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
 +
 +			if (raw_smp_processor_id() == cpu ||
 +			    !(atomic_add_return(0, &rdtp->dynticks) & 0x1))
 +				mask_ofl_test |= rdp->grpmask;
 +		}
 +		mask_ofl_ipi = rnp->expmask & ~mask_ofl_test;
 +
 +		/*
 +		 * Need to wait for any blocked tasks as well.  Note that
 +		 * additional blocking tasks will also block the expedited
 +		 * GP until such time as the ->expmask bits are cleared.
 +		 */
 +		if (rcu_preempt_has_tasks(rnp))
 +			rnp->exp_tasks = rnp->blkd_tasks.next;
 +		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 +
 +		/* IPI the remaining CPUs for expedited quiescent state. */
 +		for_each_leaf_node_possible_cpu(rnp, cpu) {
 +			unsigned long mask = leaf_node_cpu_bit(rnp, cpu);
 +			if (!(mask_ofl_ipi & mask))
 +				continue;
 +retry_ipi:
 +			ret = smp_call_function_single(cpu, func, rsp, 0);
 +			if (!ret) {
 +				mask_ofl_ipi &= ~mask;
 +				continue;
 +			}
 +			/* Failed, raced with offline. */
 +			raw_spin_lock_irqsave_rcu_node(rnp, flags);
 +			if (cpu_online(cpu) &&
 +			    (rnp->expmask & mask)) {
 +				raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 +				schedule_timeout_uninterruptible(1);
 +				if (cpu_online(cpu) &&
 +				    (rnp->expmask & mask))
 +					goto retry_ipi;
 +				raw_spin_lock_irqsave_rcu_node(rnp, flags);
 +			}
 +			if (!(rnp->expmask & mask))
 +				mask_ofl_ipi &= ~mask;
 +			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 +		}
 +		/* Report quiescent states for those that went offline. */
 +		mask_ofl_test |= mask_ofl_ipi;
 +		if (mask_ofl_test)
 +			rcu_report_exp_cpu_mult(rsp, rnp, mask_ofl_test, false);
 +	}
 +}
 +
 +static void synchronize_sched_expedited_wait(struct rcu_state *rsp)
 +{
 +	int cpu;
 +	unsigned long jiffies_stall;
 +	unsigned long jiffies_start;
 +	unsigned long mask;
 +	int ndetected;
 +	struct rcu_node *rnp;
 +	struct rcu_node *rnp_root = rcu_get_root(rsp);
 +	int ret;
 +
 +	jiffies_stall = rcu_jiffies_till_stall_check();
 +	jiffies_start = jiffies;
 +
 +	for (;;) {
 +		ret = swait_event_timeout(
 +				rsp->expedited_wq,
 +				sync_rcu_preempt_exp_done(rnp_root),
 +				jiffies_stall);
 +		if (ret > 0 || sync_rcu_preempt_exp_done(rnp_root))
 +			return;
 +		if (ret < 0) {
 +			/* Hit a signal, disable CPU stall warnings. */
 +			swait_event(rsp->expedited_wq,
 +				   sync_rcu_preempt_exp_done(rnp_root));
 +			return;
 +		}
 +		pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {",
 +		       rsp->name);
 +		ndetected = 0;
 +		rcu_for_each_leaf_node(rsp, rnp) {
 +			ndetected += rcu_print_task_exp_stall(rnp);
 +			for_each_leaf_node_possible_cpu(rnp, cpu) {
 +				struct rcu_data *rdp;
 +
 +				mask = leaf_node_cpu_bit(rnp, cpu);
 +				if (!(rnp->expmask & mask))
 +					continue;
 +				ndetected++;
 +				rdp = per_cpu_ptr(rsp->rda, cpu);
 +				pr_cont(" %d-%c%c%c", cpu,
 +					"O."[!!cpu_online(cpu)],
 +					"o."[!!(rdp->grpmask & rnp->expmaskinit)],
 +					"N."[!!(rdp->grpmask & rnp->expmaskinitnext)]);
 +			}
 +		}
 +		pr_cont(" } %lu jiffies s: %lu root: %#lx/%c\n",
 +			jiffies - jiffies_start, rsp->expedited_sequence,
 +			rnp_root->expmask, ".T"[!!rnp_root->exp_tasks]);
 +		if (ndetected) {
 +			pr_err("blocking rcu_node structures:");
 +			rcu_for_each_node_breadth_first(rsp, rnp) {
 +				if (rnp == rnp_root)
 +					continue; /* printed unconditionally */
 +				if (sync_rcu_preempt_exp_done(rnp))
 +					continue;
 +				pr_cont(" l=%u:%d-%d:%#lx/%c",
 +					rnp->level, rnp->grplo, rnp->grphi,
 +					rnp->expmask,
 +					".T"[!!rnp->exp_tasks]);
 +			}
 +			pr_cont("\n");
 +		}
 +		rcu_for_each_leaf_node(rsp, rnp) {
 +			for_each_leaf_node_possible_cpu(rnp, cpu) {
 +				mask = leaf_node_cpu_bit(rnp, cpu);
 +				if (!(rnp->expmask & mask))
 +					continue;
 +				dump_cpu_task(cpu);
 +			}
 +		}
 +		jiffies_stall = 3 * rcu_jiffies_till_stall_check() + 3;
 +	}
 +}
 +
 +/*
 + * Wait for the current expedited grace period to complete, and then
 + * wake up everyone who piggybacked on the just-completed expedited
 + * grace period.  Also update all the ->exp_seq_rq counters as needed
 + * in order to avoid counter-wrap problems.
 + */
 +static void rcu_exp_wait_wake(struct rcu_state *rsp, unsigned long s)
 +{
 +	struct rcu_node *rnp;
 +
 +	synchronize_sched_expedited_wait(rsp);
 +	rcu_exp_gp_seq_end(rsp);
 +	trace_rcu_exp_grace_period(rsp->name, s, TPS("end"));
 +
 +	/*
 +	 * Switch over to wakeup mode, allowing the next GP, but -only- the
 +	 * next GP, to proceed.
 +	 */
 +	mutex_lock(&rsp->exp_wake_mutex);
 +	mutex_unlock(&rsp->exp_mutex);
 +
 +	rcu_for_each_node_breadth_first(rsp, rnp) {
 +		if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s)) {
 +			spin_lock(&rnp->exp_lock);
 +			/* Recheck, avoid hang in case someone just arrived. */
 +			if (ULONG_CMP_LT(rnp->exp_seq_rq, s))
 +				rnp->exp_seq_rq = s;
 +			spin_unlock(&rnp->exp_lock);
 +		}
 +		wake_up_all(&rnp->exp_wq[(rsp->expedited_sequence >> 1) & 0x3]);
 +	}
 +	trace_rcu_exp_grace_period(rsp->name, s, TPS("endwake"));
 +	mutex_unlock(&rsp->exp_wake_mutex);
 +}
 +
 +/**
 + * synchronize_sched_expedited - Brute-force RCU-sched grace period
 + *
 + * Wait for an RCU-sched grace period to elapse, but use a "big hammer"
 + * approach to force the grace period to end quickly.  This consumes
 + * significant time on all CPUs and is unfriendly to real-time workloads,
 + * so is thus not recommended for any sort of common-case code.  In fact,
 + * if you are using synchronize_sched_expedited() in a loop, please
 + * restructure your code to batch your updates, and then use a single
 + * synchronize_sched() instead.
 + *
 + * This implementation can be thought of as an application of sequence
 + * locking to expedited grace periods, but using the sequence counter to
 + * determine when someone else has already done the work instead of for
 + * retrying readers.
 + */
 +void synchronize_sched_expedited(void)
 +{
 +	unsigned long s;
 +	struct rcu_state *rsp = &rcu_sched_state;
 +
 +	/* If only one CPU, this is automatically a grace period. */
 +	if (rcu_blocking_is_gp())
 +		return;
 +
 +	/* If expedited grace periods are prohibited, fall back to normal. */
 +	if (rcu_gp_is_normal()) {
 +		wait_rcu_gp(call_rcu_sched);
 +		return;
 +	}
 +
 +	/* Take a snapshot of the sequence number.  */
 +	s = rcu_exp_gp_seq_snap(rsp);
 +	if (exp_funnel_lock(rsp, s))
 +		return;  /* Someone else did our work for us. */
 +
 +	/* Initialize the rcu_node tree in preparation for the wait. */
 +	sync_rcu_exp_select_cpus(rsp, sync_sched_exp_handler);
 +
 +	/* Wait and clean up, including waking everyone. */
 +	rcu_exp_wait_wake(rsp, s);
 +}
 +EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
 +
 +#ifdef CONFIG_PREEMPT_RCU
 +
 +/*
 + * Remote handler for smp_call_function_single().  If there is an
 + * RCU read-side critical section in effect, request that the
 + * next rcu_read_unlock() record the quiescent state up the
 + * ->expmask fields in the rcu_node tree.  Otherwise, immediately
 + * report the quiescent state.
 + */
 +static void sync_rcu_exp_handler(void *info)
 +{
 +	struct rcu_data *rdp;
 +	struct rcu_state *rsp = info;
 +	struct task_struct *t = current;
 +
 +	/*
 +	 * Within an RCU read-side critical section, request that the next
 +	 * rcu_read_unlock() report.  Unless this RCU read-side critical
 +	 * section has already blocked, in which case it is already set
 +	 * up for the expedited grace period to wait on it.
 +	 */
 +	if (t->rcu_read_lock_nesting > 0 &&
 +	    !t->rcu_read_unlock_special.b.blocked) {
 +		t->rcu_read_unlock_special.b.exp_need_qs = true;
 +		return;
 +	}
 +
 +	/*
 +	 * We are either exiting an RCU read-side critical section (negative
 +	 * values of t->rcu_read_lock_nesting) or are not in one at all
 +	 * (zero value of t->rcu_read_lock_nesting).  Or we are in an RCU
 +	 * read-side critical section that blocked before this expedited
 +	 * grace period started.  Either way, we can immediately report
 +	 * the quiescent state.
 +	 */
 +	rdp = this_cpu_ptr(rsp->rda);
 +	rcu_report_exp_rdp(rsp, rdp, true);
 +}
 +
 +/**
 + * synchronize_rcu_expedited - Brute-force RCU grace period
 + *
 + * Wait for an RCU-preempt grace period, but expedite it.  The basic
 + * idea is to IPI all non-idle non-nohz online CPUs.  The IPI handler
 + * checks whether the CPU is in an RCU-preempt critical section, and
 + * if so, it sets a flag that causes the outermost rcu_read_unlock()
 + * to report the quiescent state.  On the other hand, if the CPU is
 + * not in an RCU read-side critical section, the IPI handler reports
 + * the quiescent state immediately.
 + *
 + * Although this is a greate improvement over previous expedited
 + * implementations, it is still 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.
 + */
 +void synchronize_rcu_expedited(void)
 +{
 +	struct rcu_state *rsp = rcu_state_p;
 +	unsigned long s;
 +
 +	/* If expedited grace periods are prohibited, fall back to normal. */
 +	if (rcu_gp_is_normal()) {
 +		wait_rcu_gp(call_rcu);
 +		return;
 +	}
 +
 +	s = rcu_exp_gp_seq_snap(rsp);
 +	if (exp_funnel_lock(rsp, s))
 +		return;  /* Someone else did our work for us. */
 +
 +	/* Initialize the rcu_node tree in preparation for the wait. */
 +	sync_rcu_exp_select_cpus(rsp, sync_rcu_exp_handler);
 +
 +	/* Wait for ->blkd_tasks lists to drain, then wake everyone up. */
 +	rcu_exp_wait_wake(rsp, s);
 +}
 +EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
 +
 +#else /* #ifdef CONFIG_PREEMPT_RCU */
 +
 +/*
 + * Wait for an rcu-preempt grace period, but make it happen quickly.
 + * But because preemptible RCU does not exist, map to rcu-sched.
 + */
 +void synchronize_rcu_expedited(void)
 +{
 +	synchronize_sched_expedited();
 +}
 +EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
 +
 +#endif /* #else #ifdef CONFIG_PREEMPT_RCU */