Merge branch 'core-rcu-for-linus' of...

Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: (31 commits)
  rcu: Make RCU's CPU-stall detector be default
  rcu: Add expedited grace-period support for preemptible RCU
  rcu: Enable fourth level of TREE_RCU hierarchy
  rcu: Rename "quiet" functions
  rcu: Re-arrange code to reduce #ifdef pain
  rcu: Eliminate unneeded function wrapping
  rcu: Fix grace-period-stall bug on large systems with CPU hotplug
  rcu: Eliminate __rcu_pending() false positives
  rcu: Further cleanups of use of lastcomp
  rcu: Simplify association of forced quiescent states with grace periods
  rcu: Accelerate callback processing on CPUs not detecting GP end
  rcu: Mark init-time-only rcu_bootup_announce() as __init
  rcu: Simplify association of quiescent states with grace periods
  rcu: Rename dynticks_completed to completed_fqs
  rcu: Enable synchronize_sched_expedited() fastpath
  rcu: Remove inline from forward-referenced functions
  rcu: Fix note_new_gpnum() uses of ->gpnum
  rcu: Fix synchronization for rcu_process_gp_end() uses of ->completed counter
  rcu: Prepare for synchronization fixes: clean up for non-NO_HZ handling of ->completed counter
  rcu: Cleanup: balance rcu_irq_enter()/rcu_irq_exit() calls
  ...

Documentation/RCU/whatisRCU.txt

@@ -830,7 +830,7 @@ sched:	Critical sections	Grace period		Barrier
 SRCU:	Critical sections	Grace period		Barrier
 
 	srcu_read_lock		synchronize_srcu	N/A
-	srcu_read_unlock
+	srcu_read_unlock	synchronize_srcu_expedited
 
 SRCU:	Initialization/cleanup
 	init_srcu_struct

include/linux/hardirq.h

@@ -139,10 +139,34 @@ static inline void account_system_vtime(struct task_struct *tsk)
 #endif
 
 #if defined(CONFIG_NO_HZ)
+#if defined(CONFIG_TINY_RCU)
+extern void rcu_enter_nohz(void);
+extern void rcu_exit_nohz(void);
+
+static inline void rcu_irq_enter(void)
+{
+	rcu_exit_nohz();
+}
+
+static inline void rcu_irq_exit(void)
+{
+	rcu_enter_nohz();
+}
+
+static inline void rcu_nmi_enter(void)
+{
+}
+
+static inline void rcu_nmi_exit(void)
+{
+}
+
+#else
 extern void rcu_irq_enter(void);
 extern void rcu_irq_exit(void);
 extern void rcu_nmi_enter(void);
 extern void rcu_nmi_exit(void);
+#endif
 #else
 # define rcu_irq_enter() do { } while (0)
 # define rcu_irq_exit() do { } while (0)

include/linux/rcupdate.h

@@ -52,11 +52,6 @@ struct rcu_head {
 };
 
 /* Exported common interfaces */
-#ifdef CONFIG_TREE_PREEMPT_RCU
-extern void synchronize_rcu(void);
-#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
-#define synchronize_rcu synchronize_sched
-#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
 extern void synchronize_rcu_bh(void);
 extern void synchronize_sched(void);
 extern void rcu_barrier(void);
@@ -67,12 +62,11 @@ extern int sched_expedited_torture_stats(char *page);
 
 /* Internal to kernel */
 extern void rcu_init(void);
-extern void rcu_scheduler_starting(void);
-extern int rcu_needs_cpu(int cpu);
-extern int rcu_scheduler_active;
 
 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
 #include <linux/rcutree.h>
+#elif defined(CONFIG_TINY_RCU)
+#include <linux/rcutiny.h>
 #else
 #error "Unknown RCU implementation specified to kernel configuration"
 #endif

include/linux/rcutiny.h

+/*
+ * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition.
+ *
+ * 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 IBM Corporation, 2008
+ *
+ * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
+ *
+ * For detailed explanation of Read-Copy Update mechanism see -
+ *		Documentation/RCU
+ */
+#ifndef __LINUX_TINY_H
+#define __LINUX_TINY_H
+
+#include <linux/cache.h>
+
+void rcu_sched_qs(int cpu);
+void rcu_bh_qs(int cpu);
+
+#define __rcu_read_lock()	preempt_disable()
+#define __rcu_read_unlock()	preempt_enable()
+#define __rcu_read_lock_bh()	local_bh_disable()
+#define __rcu_read_unlock_bh()	local_bh_enable()
+#define call_rcu_sched		call_rcu
+
+#define rcu_init_sched()	do { } while (0)
+extern void rcu_check_callbacks(int cpu, int user);
+
+static inline int rcu_needs_cpu(int cpu)
+{
+	return 0;
+}
+
+/*
+ * Return the number of grace periods.
+ */
+static inline long rcu_batches_completed(void)
+{
+	return 0;
+}
+
+/*
+ * Return the number of bottom-half grace periods.
+ */
+static inline long rcu_batches_completed_bh(void)
+{
+	return 0;
+}
+
+extern int rcu_expedited_torture_stats(char *page);
+
+#define synchronize_rcu synchronize_sched
+
+static inline void synchronize_rcu_expedited(void)
+{
+	synchronize_sched();
+}
+
+static inline void synchronize_rcu_bh_expedited(void)
+{
+	synchronize_sched();
+}
+
+struct notifier_block;
+
+#ifdef CONFIG_NO_HZ
+
+extern void rcu_enter_nohz(void);
+extern void rcu_exit_nohz(void);
+
+#else /* #ifdef CONFIG_NO_HZ */
+
+static inline void rcu_enter_nohz(void)
+{
+}
+
+static inline void rcu_exit_nohz(void)
+{
+}
+
+#endif /* #else #ifdef CONFIG_NO_HZ */
+
+static inline void rcu_scheduler_starting(void)
+{
+}
+
+static inline void exit_rcu(void)
+{
+}
+
+#endif /* __LINUX_RCUTINY_H */

include/linux/rcutree.h

@@ -34,15 +34,15 @@ struct notifier_block;
 
 extern void rcu_sched_qs(int cpu);
 extern void rcu_bh_qs(int cpu);
-extern int rcu_cpu_notify(struct notifier_block *self,
-			  unsigned long action, void *hcpu);
 extern int rcu_needs_cpu(int cpu);
+extern void rcu_scheduler_starting(void);
 extern int rcu_expedited_torture_stats(char *page);
 
 #ifdef CONFIG_TREE_PREEMPT_RCU
 
 extern void __rcu_read_lock(void);
 extern void __rcu_read_unlock(void);
+extern void synchronize_rcu(void);
 extern void exit_rcu(void);
 
 #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
@@ -57,7 +57,7 @@ static inline void __rcu_read_unlock(void)
 	preempt_enable();
 }
 
-#define __synchronize_sched() synchronize_rcu()
+#define synchronize_rcu synchronize_sched
 
 static inline void exit_rcu(void)
 {
@@ -83,7 +83,6 @@ static inline void synchronize_rcu_bh_expedited(void)
 	synchronize_sched_expedited();
 }
 
-extern void __rcu_init(void);
 extern void rcu_check_callbacks(int cpu, int user);
 
 extern long rcu_batches_completed(void);

include/linux/srcu.h

@@ -48,6 +48,7 @@ void cleanup_srcu_struct(struct srcu_struct *sp);
 int srcu_read_lock(struct srcu_struct *sp) __acquires(sp);
 void srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp);
 void synchronize_srcu(struct srcu_struct *sp);
+void synchronize_srcu_expedited(struct srcu_struct *sp);
 long srcu_batches_completed(struct srcu_struct *sp);
 
 #endif

init/Kconfig

@@ -334,6 +334,15 @@ config TREE_PREEMPT_RCU
 	  is also required.  It also scales down nicely to
 	  smaller systems.
 
+config TINY_RCU
+	bool "UP-only small-memory-footprint RCU"
+	depends on !SMP
+	help
+	  This option selects the RCU implementation that is
+	  designed for UP systems from which real-time response
+	  is not required.  This option greatly reduces the
+	  memory footprint of RCU.
+
 endchoice
 
 config RCU_TRACE

kernel/Makefile

@@ -82,6 +82,7 @@ obj-$(CONFIG_RCU_TORTURE_TEST) += rcutorture.o
 obj-$(CONFIG_TREE_RCU) += rcutree.o
 obj-$(CONFIG_TREE_PREEMPT_RCU) += rcutree.o
 obj-$(CONFIG_TREE_RCU_TRACE) += rcutree_trace.o
+obj-$(CONFIG_TINY_RCU) += rcutiny.o
 obj-$(CONFIG_RELAY) += relay.o
 obj-$(CONFIG_SYSCTL) += utsname_sysctl.o
 obj-$(CONFIG_TASK_DELAY_ACCT) += delayacct.o

kernel/rcupdate.c

@@ -44,7 +44,6 @@
 #include <linux/cpu.h>
 #include <linux/mutex.h>
 #include <linux/module.h>
-#include <linux/kernel_stat.h>
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 static struct lock_class_key rcu_lock_key;
@@ -53,8 +52,6 @@ struct lockdep_map rcu_lock_map =
 EXPORT_SYMBOL_GPL(rcu_lock_map);
 #endif
 
-int rcu_scheduler_active __read_mostly;
-
 /*
  * Awaken the corresponding synchronize_rcu() instance now that a
  * grace period has elapsed.
@@ -66,122 +63,3 @@ void wakeme_after_rcu(struct rcu_head  *head)
 	rcu = container_of(head, struct rcu_synchronize, head);
 	complete(&rcu->completion);
 }
-
-#ifdef CONFIG_TREE_PREEMPT_RCU
-
-/**
- * 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
- * read-side critical sections have completed.  RCU read-side critical
- * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
- * and may be nested.
- */
-void synchronize_rcu(void)
-{
-	struct rcu_synchronize rcu;
-
-	if (!rcu_scheduler_active)
-		return;
-
-	init_completion(&rcu.completion);
-	/* Will wake me after RCU finished. */
-	call_rcu(&rcu.head, wakeme_after_rcu);
-	/* Wait for it. */
-	wait_for_completion(&rcu.completion);
-}
-EXPORT_SYMBOL_GPL(synchronize_rcu);
-
-#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
-
-/**
- * synchronize_sched - wait until an rcu-sched grace period has elapsed.
- *
- * Control will return to the caller some time after a full rcu-sched
- * grace period has elapsed, in other words after all currently executing
- * rcu-sched read-side critical sections have completed.   These read-side
- * critical sections are delimited by rcu_read_lock_sched() and
- * rcu_read_unlock_sched(), and may be nested.  Note that preempt_disable(),
- * local_irq_disable(), and so on may be used in place of
- * rcu_read_lock_sched().
- *
- * This means that all preempt_disable code sequences, including NMI and
- * hardware-interrupt handlers, in progress on entry will have completed
- * before this primitive returns.  However, this does not guarantee that
- * softirq handlers will have completed, since in some kernels, these
- * handlers can run in process context, and can block.
- *
- * This primitive provides the guarantees made by the (now removed)
- * synchronize_kernel() API.  In contrast, synchronize_rcu() only
- * guarantees that rcu_read_lock() sections will have completed.
- * In "classic RCU", these two guarantees happen to be one and
- * the same, but can differ in realtime RCU implementations.
- */
-void synchronize_sched(void)
-{
-	struct rcu_synchronize rcu;
-
-	if (rcu_blocking_is_gp())
-		return;
-
-	init_completion(&rcu.completion);
-	/* Will wake me after RCU finished. */
-	call_rcu_sched(&rcu.head, wakeme_after_rcu);
-	/* Wait for it. */
-	wait_for_completion(&rcu.completion);
-}
-EXPORT_SYMBOL_GPL(synchronize_sched);
-
-/**
- * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
- *
- * Control will return to the caller some time after a full rcu_bh grace
- * period has elapsed, in other words after all currently executing rcu_bh
- * read-side critical sections have completed.  RCU read-side critical
- * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
- * and may be nested.
- */
-void synchronize_rcu_bh(void)
-{
-	struct rcu_synchronize rcu;
-
-	if (rcu_blocking_is_gp())
-		return;
-
-	init_completion(&rcu.completion);
-	/* Will wake me after RCU finished. */
-	call_rcu_bh(&rcu.head, wakeme_after_rcu);
-	/* Wait for it. */
-	wait_for_completion(&rcu.completion);
-}
-EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
-
-static int __cpuinit rcu_barrier_cpu_hotplug(struct notifier_block *self,
-		unsigned long action, void *hcpu)
-{
-	return rcu_cpu_notify(self, action, hcpu);
-}
-
-void __init rcu_init(void)
-{
-	int i;
-
-	__rcu_init();
-	cpu_notifier(rcu_barrier_cpu_hotplug, 0);
-
-	/*
-	 * We don't need protection against CPU-hotplug here because
-	 * this is called early in boot, before either interrupts
-	 * or the scheduler are operational.
-	 */
-	for_each_online_cpu(i)
-		rcu_barrier_cpu_hotplug(NULL, CPU_UP_PREPARE, (void *)(long)i);
-}
-
-void rcu_scheduler_starting(void)
-{
-	WARN_ON(num_online_cpus() != 1);
-	WARN_ON(nr_context_switches() > 0);
-	rcu_scheduler_active = 1;
-}

kernel/rcutiny.c

+/*
+ * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition.
+ *
+ * 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 IBM Corporation, 2008
+ *
+ * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
+ *
+ * For detailed explanation of Read-Copy Update mechanism see -
+ *		Documentation/RCU
+ */
+#include <linux/moduleparam.h>
+#include <linux/completion.h>
+#include <linux/interrupt.h>
+#include <linux/notifier.h>
+#include <linux/rcupdate.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/sched.h>
+#include <linux/types.h>
+#include <linux/init.h>
+#include <linux/time.h>
+#include <linux/cpu.h>
+
+/* Global control variables for rcupdate callback mechanism. */
+struct rcu_ctrlblk {
+	struct rcu_head *rcucblist;	/* List of pending callbacks (CBs). */
+	struct rcu_head **donetail;	/* ->next pointer of last "done" CB. */
+	struct rcu_head **curtail;	/* ->next pointer of last CB. */
+};
+
+/* Definition for rcupdate control block. */
+static struct rcu_ctrlblk rcu_ctrlblk = {
+	.donetail	= &rcu_ctrlblk.rcucblist,
+	.curtail	= &rcu_ctrlblk.rcucblist,
+};
+
+static struct rcu_ctrlblk rcu_bh_ctrlblk = {
+	.donetail	= &rcu_bh_ctrlblk.rcucblist,
+	.curtail	= &rcu_bh_ctrlblk.rcucblist,
+};
+
+#ifdef CONFIG_NO_HZ
+
+static long rcu_dynticks_nesting = 1;
+
+/*
+ * Enter dynticks-idle mode, which is an extended quiescent state
+ * if we have fully entered that mode (i.e., if the new value of
+ * dynticks_nesting is zero).
+ */
+void rcu_enter_nohz(void)
+{
+	if (--rcu_dynticks_nesting == 0)
+		rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
+}
+
+/*
+ * Exit dynticks-idle mode, so that we are no longer in an extended
+ * quiescent state.
+ */
+void rcu_exit_nohz(void)
+{
+	rcu_dynticks_nesting++;
+}
+
+#endif /* #ifdef CONFIG_NO_HZ */
+
+/*
+ * Helper function for rcu_qsctr_inc() and rcu_bh_qsctr_inc().
+ * Also disable irqs to avoid confusion due to interrupt handlers
+ * invoking call_rcu().
+ */
+static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
+{
+	unsigned long flags;
+
+	local_irq_save(flags);
+	if (rcp->rcucblist != NULL &&
+	    rcp->donetail != rcp->curtail) {
+		rcp->donetail = rcp->curtail;
+		local_irq_restore(flags);
+		return 1;
+	}
+	local_irq_restore(flags);
+
+	return 0;
+}
+
+/*
+ * Record an rcu quiescent state.  And an rcu_bh quiescent state while we
+ * are at it, given that any rcu quiescent state is also an rcu_bh
+ * quiescent state.  Use "+" instead of "||" to defeat short circuiting.
+ */
+void rcu_sched_qs(int cpu)
+{
+	if (rcu_qsctr_help(&rcu_ctrlblk) + rcu_qsctr_help(&rcu_bh_ctrlblk))
+		raise_softirq(RCU_SOFTIRQ);
+}
+
+/*
+ * Record an rcu_bh quiescent state.
+ */
+void rcu_bh_qs(int cpu)
+{
+	if (rcu_qsctr_help(&rcu_bh_ctrlblk))
+		raise_softirq(RCU_SOFTIRQ);
+}
+
+/*
+ * Check to see if the scheduling-clock interrupt came from an extended
+ * quiescent state, and, if so, tell RCU about it.
+ */
+void rcu_check_callbacks(int cpu, int user)
+{
+	if (user ||
+	    (idle_cpu(cpu) &&
+	     !in_softirq() &&
+	     hardirq_count() <= (1 << HARDIRQ_SHIFT)))
+		rcu_sched_qs(cpu);
+	else if (!in_softirq())
+		rcu_bh_qs(cpu);
+}
+
+/*
+ * Helper function for rcu_process_callbacks() that operates on the
+ * specified rcu_ctrlkblk structure.
+ */
+static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
+{
+	struct rcu_head *next, *list;
+	unsigned long flags;
+
+	/* If no RCU callbacks ready to invoke, just return. */
+	if (&rcp->rcucblist == rcp->donetail)
+		return;
+
+	/* Move the ready-to-invoke callbacks to a local list. */
+	local_irq_save(flags);
+	list = rcp->rcucblist;
+	rcp->rcucblist = *rcp->donetail;
+	*rcp->donetail = NULL;
+	if (rcp->curtail == rcp->donetail)
+		rcp->curtail = &rcp->rcucblist;
+	rcp->donetail = &rcp->rcucblist;
+	local_irq_restore(flags);
+
+	/* Invoke the callbacks on the local list. */
+	while (list) {
+		next = list->next;
+		prefetch(next);
+		list->func(list);
+		list = next;
+	}
+}
+
+/*
+ * Invoke any callbacks whose grace period has completed.
+ */
+static void rcu_process_callbacks(struct softirq_action *unused)
+{
+	__rcu_process_callbacks(&rcu_ctrlblk);
+	__rcu_process_callbacks(&rcu_bh_ctrlblk);
+}
+
+/*
+ * Wait for a grace period to elapse.  But it is illegal to invoke
+ * synchronize_sched() from within an RCU read-side critical section.
+ * Therefore, any legal call to synchronize_sched() is a quiescent
+ * state, and so on a UP system, synchronize_sched() need do nothing.
+ * Ditto for synchronize_rcu_bh().  (But Lai Jiangshan points out the
+ * benefits of doing might_sleep() to reduce latency.)
+ *
+ * Cool, huh?  (Due to Josh Triplett.)
+ *
+ * But we want to make this a static inline later.
+ */
+void synchronize_sched(void)
+{
+	cond_resched();
+}
+EXPORT_SYMBOL_GPL(synchronize_sched);
+
+void synchronize_rcu_bh(void)
+{
+	synchronize_sched();
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
+
+/*
+ * Helper function for call_rcu() and call_rcu_bh().
+ */
+static void __call_rcu(struct rcu_head *head,
+		       void (*func)(struct rcu_head *rcu),
+		       struct rcu_ctrlblk *rcp)
+{
+	unsigned long flags;
+
+	head->func = func;
+	head->next = NULL;
+
+	local_irq_save(flags);
+	*rcp->curtail = head;
+	rcp->curtail = &head->next;
+	local_irq_restore(flags);
+}
+
+/*
+ * Post an RCU callback to be invoked after the end of an RCU grace
+ * period.  But since we have but one CPU, that would be after any
+ * quiescent state.
+ */
+void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
+{
+	__call_rcu(head, func, &rcu_ctrlblk);
+}
+EXPORT_SYMBOL_GPL(call_rcu);
+
+/*
+ * Post an RCU bottom-half callback to be invoked after any subsequent
+ * quiescent state.
+ */
+void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
+{
+	__call_rcu(head, func, &rcu_bh_ctrlblk);
+}
+EXPORT_SYMBOL_GPL(call_rcu_bh);
+
+void rcu_barrier(void)
+{
+	struct rcu_synchronize rcu;
+
+	init_completion(&rcu.completion);
+	/* Will wake me after RCU finished. */
+	call_rcu(&rcu.head, wakeme_after_rcu);
+	/* Wait for it. */
+	wait_for_completion(&rcu.completion);
+}
+EXPORT_SYMBOL_GPL(rcu_barrier);
+
+void rcu_barrier_bh(void)
+{
+	struct rcu_synchronize rcu;
+
+	init_completion(&rcu.completion);
+	/* Will wake me after RCU finished. */
+	call_rcu_bh(&rcu.head, wakeme_after_rcu);
+	/* Wait for it. */
+	wait_for_completion(&rcu.completion);
+}
+EXPORT_SYMBOL_GPL(rcu_barrier_bh);
+
+void rcu_barrier_sched(void)
+{
+	struct rcu_synchronize rcu;
+
+	init_completion(&rcu.completion);
+	/* Will wake me after RCU finished. */
+	call_rcu_sched(&rcu.head, wakeme_after_rcu);
+	/* Wait for it. */
+	wait_for_completion(&rcu.completion);
+}
+EXPORT_SYMBOL_GPL(rcu_barrier_sched);
+
+void __init rcu_init(void)
+{
+	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
+}

kernel/rcutorture.c

@@ -327,6 +327,11 @@ rcu_torture_cb(struct rcu_head *p)
 		cur_ops->deferred_free(rp);
 }
 
+static int rcu_no_completed(void)
+{
+	return 0;
+}
+
 static void rcu_torture_deferred_free(struct rcu_torture *p)
 {
 	call_rcu(&p->rtort_rcu, rcu_torture_cb);
@@ -388,6 +393,21 @@ static struct rcu_torture_ops rcu_sync_ops = {
 	.name		= "rcu_sync"
 };
 
+static struct rcu_torture_ops rcu_expedited_ops = {
+	.init		= rcu_sync_torture_init,
+	.cleanup	= NULL,
+	.readlock	= rcu_torture_read_lock,
+	.read_delay	= rcu_read_delay,  /* just reuse rcu's version. */
+	.readunlock	= rcu_torture_read_unlock,
+	.completed	= rcu_no_completed,
+	.deferred_free	= rcu_sync_torture_deferred_free,
+	.sync		= synchronize_rcu_expedited,
+	.cb_barrier	= NULL,
+	.stats		= NULL,
+	.irq_capable	= 1,
+	.name		= "rcu_expedited"
+};
+
 /*
  * Definitions for rcu_bh torture testing.
  */
@@ -547,6 +567,25 @@ static struct rcu_torture_ops srcu_ops = {
 	.name		= "srcu"
 };
 
+static void srcu_torture_synchronize_expedited(void)
+{
+	synchronize_srcu_expedited(&srcu_ctl);
+}
+
+static struct rcu_torture_ops srcu_expedited_ops = {
+	.init		= srcu_torture_init,
+	.cleanup	= srcu_torture_cleanup,
+	.readlock	= srcu_torture_read_lock,
+	.read_delay	= srcu_read_delay,
+	.readunlock	= srcu_torture_read_unlock,
+	.completed	= srcu_torture_completed,
+	.deferred_free	= rcu_sync_torture_deferred_free,
+	.sync		= srcu_torture_synchronize_expedited,
+	.cb_barrier	= NULL,
+	.stats		= srcu_torture_stats,
+	.name		= "srcu_expedited"
+};
+
 /*
  * Definitions for sched torture testing.
  */
@@ -562,11 +601,6 @@ static void sched_torture_read_unlock(int idx)
 	preempt_enable();
 }
 
-static int sched_torture_completed(void)
-{
-	return 0;
-}
-
 static void rcu_sched_torture_deferred_free(struct rcu_torture *p)
 {
 	call_rcu_sched(&p->rtort_rcu, rcu_torture_cb);
@@ -583,7 +617,7 @@ static struct rcu_torture_ops sched_ops = {
 	.readlock	= sched_torture_read_lock,
 	.read_delay	= rcu_read_delay,  /* just reuse rcu's version. */
 	.readunlock	= sched_torture_read_unlock,
-	.completed	= sched_torture_completed,
+	.completed	= rcu_no_completed,
 	.deferred_free	= rcu_sched_torture_deferred_free,
 	.sync		= sched_torture_synchronize,
 	.cb_barrier	= rcu_barrier_sched,
@@ -592,13 +626,13 @@ static struct rcu_torture_ops sched_ops = {
 	.name		= "sched"
 };
 
-static struct rcu_torture_ops sched_ops_sync = {
+static struct rcu_torture_ops sched_sync_ops = {
 	.init		= rcu_sync_torture_init,
 	.cleanup	= NULL,
 	.readlock	= sched_torture_read_lock,
 	.read_delay	= rcu_read_delay,  /* just reuse rcu's version. */
 	.readunlock	= sched_torture_read_unlock,
-	.completed	= sched_torture_completed,
+	.completed	= rcu_no_completed,
 	.deferred_free	= rcu_sync_torture_deferred_free,
 	.sync		= sched_torture_synchronize,
 	.cb_barrier	= NULL,
@@ -612,7 +646,7 @@ static struct rcu_torture_ops sched_expedited_ops = {
 	.readlock	= sched_torture_read_lock,
 	.read_delay	= rcu_read_delay,  /* just reuse rcu's version. */
 	.readunlock	= sched_torture_read_unlock,
-	.completed	= sched_torture_completed,
+	.completed	= rcu_no_completed,
 	.deferred_free	= rcu_sync_torture_deferred_free,
 	.sync		= synchronize_sched_expedited,
 	.cb_barrier	= NULL,
@@ -1097,9 +1131,10 @@ rcu_torture_init(void)
 	int cpu;
 	int firsterr = 0;
 	static struct rcu_torture_ops *torture_ops[] =
-		{ &rcu_ops, &rcu_sync_ops, &rcu_bh_ops, &rcu_bh_sync_ops,
-		  &sched_expedited_ops,
-		  &srcu_ops, &sched_ops, &sched_ops_sync, };
+		{ &rcu_ops, &rcu_sync_ops, &rcu_expedited_ops,
+		  &rcu_bh_ops, &rcu_bh_sync_ops,
+		  &srcu_ops, &srcu_expedited_ops,
+		  &sched_ops, &sched_sync_ops, &sched_expedited_ops, };
 
 	mutex_lock(&fullstop_mutex);
 
@@ -1110,8 +1145,12 @@ rcu_torture_init(void)
 			break;
 	}
 	if (i == ARRAY_SIZE(torture_ops)) {
-		printk(KERN_ALERT "rcutorture: invalid torture type: \"%s\"\n",
+		printk(KERN_ALERT "rcu-torture: invalid torture type: \"%s\"\n",
 		       torture_type);
+		printk(KERN_ALERT "rcu-torture types:");
+		for (i = 0; i < ARRAY_SIZE(torture_ops); i++)
+			printk(KERN_ALERT " %s", torture_ops[i]->name);
+		printk(KERN_ALERT "\n");
 		mutex_unlock(&fullstop_mutex);
 		return -EINVAL;
 	}

kernel/rcutree.h

@@ -34,10 +34,11 @@
  * In practice, this has not been tested, so there is probably some
  * bug somewhere.
  */
-#define MAX_RCU_LVLS 3
+#define MAX_RCU_LVLS 4
 #define RCU_FANOUT	      (CONFIG_RCU_FANOUT)
 #define RCU_FANOUT_SQ	      (RCU_FANOUT * RCU_FANOUT)
 #define RCU_FANOUT_CUBE	      (RCU_FANOUT_SQ * RCU_FANOUT)
+#define RCU_FANOUT_FOURTH     (RCU_FANOUT_CUBE * RCU_FANOUT)
 
 #if NR_CPUS <= RCU_FANOUT
 #  define NUM_RCU_LVLS	      1
@@ -45,23 +46,33 @@
 #  define NUM_RCU_LVL_1	      (NR_CPUS)
 #  define NUM_RCU_LVL_2	      0
 #  define NUM_RCU_LVL_3	      0
+#  define NUM_RCU_LVL_4	      0
 #elif NR_CPUS <= RCU_FANOUT_SQ
 #  define NUM_RCU_LVLS	      2
 #  define NUM_RCU_LVL_0	      1
 #  define NUM_RCU_LVL_1	      DIV_ROUND_UP(NR_CPUS, RCU_FANOUT)
 #  define NUM_RCU_LVL_2	      (NR_CPUS)
 #  define NUM_RCU_LVL_3	      0
+#  define NUM_RCU_LVL_4	      0
 #elif NR_CPUS <= RCU_FANOUT_CUBE
 #  define NUM_RCU_LVLS	      3
 #  define NUM_RCU_LVL_0	      1
 #  define NUM_RCU_LVL_1	      DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_SQ)
 #  define NUM_RCU_LVL_2	      DIV_ROUND_UP(NR_CPUS, RCU_FANOUT)
 #  define NUM_RCU_LVL_3	      NR_CPUS
+#  define NUM_RCU_LVL_4	      0
+#elif NR_CPUS <= RCU_FANOUT_FOURTH
+#  define NUM_RCU_LVLS	      4
+#  define NUM_RCU_LVL_0	      1
+#  define NUM_RCU_LVL_1	      DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_CUBE)
+#  define NUM_RCU_LVL_2	      DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_SQ)
+#  define NUM_RCU_LVL_3	      DIV_ROUND_UP(NR_CPUS, RCU_FANOUT)
+#  define NUM_RCU_LVL_4	      NR_CPUS
 #else
 # error "CONFIG_RCU_FANOUT insufficient for NR_CPUS"
 #endif /* #if (NR_CPUS) <= RCU_FANOUT */
 
-#define RCU_SUM (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2 + NUM_RCU_LVL_3)
+#define RCU_SUM (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2 + NUM_RCU_LVL_3 + NUM_RCU_LVL_4)
 #define NUM_RCU_NODES (RCU_SUM - NR_CPUS)
 
 /*
@@ -84,14 +95,21 @@ struct rcu_node {
 	long	gpnum;		/* Current grace period for this node. */
 				/*  This will either be equal to or one */
 				/*  behind the root rcu_node's gpnum. */
+	long	completed;	/* Last grace period completed for this node. */
+				/*  This will either be equal to or one */
+				/*  behind the root rcu_node's gpnum. */
 	unsigned long qsmask;	/* CPUs or groups that need to switch in */
 				/*  order for current grace period to proceed.*/
 				/*  In leaf rcu_node, each bit corresponds to */
 				/*  an rcu_data structure, otherwise, each */
 				/*  bit corresponds to a child rcu_node */
 				/*  structure. */
+	unsigned long expmask;	/* Groups that have ->blocked_tasks[] */
+				/*  elements that need to drain to allow the */
+				/*  current expedited grace period to */
+				/*  complete (only for TREE_PREEMPT_RCU). */
 	unsigned long qsmaskinit;
-				/* Per-GP initialization for qsmask. */
+				/* Per-GP initial value for qsmask & expmask. */
 	unsigned long grpmask;	/* Mask to apply to parent qsmask. */
 				/*  Only one bit will be set in this mask. */
 	int	grplo;		/* lowest-numbered CPU or group here. */
@@ -99,7 +117,7 @@ struct rcu_node {
 	u8	grpnum;		/* CPU/group number for next level up. */
 	u8	level;		/* root is at level 0. */
 	struct rcu_node *parent;
-	struct list_head blocked_tasks[2];
+	struct list_head blocked_tasks[4];
 				/* Tasks blocked in RCU read-side critsect. */
 				/*  Grace period number (->gpnum) x blocked */
 				/*  by tasks on the (x & 0x1) element of the */
@@ -114,6 +132,21 @@ struct rcu_node {
 	for ((rnp) = &(rsp)->node[0]; \
 	     (rnp) < &(rsp)->node[NUM_RCU_NODES]; (rnp)++)
 
+/*
+ * Do a breadth-first scan of the non-leaf rcu_node structures for the
+ * specified rcu_state structure.  Note that if there is a singleton
+ * rcu_node tree with but one rcu_node structure, this loop is a no-op.
+ */
+#define rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) \
+	for ((rnp) = &(rsp)->node[0]; \
+	     (rnp) < (rsp)->level[NUM_RCU_LVLS - 1]; (rnp)++)
+
+/*
+ * Scan the leaves of the rcu_node hierarchy for the specified rcu_state
+ * structure.  Note that if there is a singleton rcu_node tree with but
+ * one rcu_node structure, this loop -will- visit the rcu_node structure.
+ * It is still a leaf node, even if it is also the root node.
+ */
 #define rcu_for_each_leaf_node(rsp, rnp) \
 	for ((rnp) = (rsp)->level[NUM_RCU_LVLS - 1]; \
 	     (rnp) < &(rsp)->node[NUM_RCU_NODES]; (rnp)++)
@@ -204,11 +237,12 @@ struct rcu_data {
 #define RCU_GP_IDLE		0	/* No grace period in progress. */
 #define RCU_GP_INIT		1	/* Grace period being initialized. */
 #define RCU_SAVE_DYNTICK	2	/* Need to scan dyntick state. */
-#define RCU_FORCE_QS		3	/* Need to force quiescent state. */
+#define RCU_SAVE_COMPLETED	3	/* Need to save rsp->completed. */
+#define RCU_FORCE_QS		4	/* Need to force quiescent state. */
 #ifdef CONFIG_NO_HZ
 #define RCU_SIGNAL_INIT		RCU_SAVE_DYNTICK
 #else /* #ifdef CONFIG_NO_HZ */
-#define RCU_SIGNAL_INIT		RCU_FORCE_QS
+#define RCU_SIGNAL_INIT		RCU_SAVE_COMPLETED
 #endif /* #else #ifdef CONFIG_NO_HZ */
 
 #define RCU_JIFFIES_TILL_FORCE_QS	 3	/* for rsp->jiffies_force_qs */
@@ -246,7 +280,7 @@ struct rcu_state {
 	long	gpnum;				/* Current gp number. */
 	long	completed;			/* # of last completed gp. */
 
-	/* End  of fields guarded by root rcu_node's lock. */
+	/* End of fields guarded by root rcu_node's lock. */
 
 	spinlock_t onofflock;			/* exclude on/offline and */
 						/*  starting new GP.  Also */
@@ -260,6 +294,8 @@ struct rcu_state {
 	long orphan_qlen;			/* Number of orphaned cbs. */
 	spinlock_t fqslock;			/* Only one task forcing */
 						/*  quiescent states. */
+	long	completed_fqs;			/* Value of completed @ snap. */
+						/*  Protected by fqslock. */
 	unsigned long jiffies_force_qs;		/* Time at which to invoke */
 						/*  force_quiescent_state(). */
 	unsigned long n_force_qs;		/* Number of calls to */
@@ -274,11 +310,15 @@ struct rcu_state {
 	unsigned long jiffies_stall;		/* Time at which to check */
 						/*  for CPU stalls. */
 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
-#ifdef CONFIG_NO_HZ
-	long dynticks_completed;		/* Value of completed @ snap. */
-#endif /* #ifdef CONFIG_NO_HZ */
 };
 
+/* Return values for rcu_preempt_offline_tasks(). */
+
+#define RCU_OFL_TASKS_NORM_GP	0x1		/* Tasks blocking normal */
+						/*  GP were moved to root. */
+#define RCU_OFL_TASKS_EXP_GP	0x2		/* Tasks blocking expedited */
+						/*  GP were moved to root. */
+
 #ifdef RCU_TREE_NONCORE
 
 /*
@@ -298,10 +338,14 @@ DECLARE_PER_CPU(struct rcu_data, rcu_preempt_data);
 #else /* #ifdef RCU_TREE_NONCORE */
 
 /* Forward declarations for rcutree_plugin.h */
-static inline void rcu_bootup_announce(void);
+static void rcu_bootup_announce(void);
 long rcu_batches_completed(void);
 static void rcu_preempt_note_context_switch(int cpu);
 static int rcu_preempted_readers(struct rcu_node *rnp);
+#ifdef CONFIG_HOTPLUG_CPU
+static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp,
+				      unsigned long flags);
+#endif /* #ifdef CONFIG_HOTPLUG_CPU */
 #ifdef CONFIG_RCU_CPU_STALL_DETECTOR
 static void rcu_print_task_stall(struct rcu_node *rnp);
 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
@@ -315,6 +359,9 @@ static void rcu_preempt_offline_cpu(int cpu);
 static void rcu_preempt_check_callbacks(int cpu);
 static void rcu_preempt_process_callbacks(void);
 void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu));
+#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_TREE_PREEMPT_RCU)
+static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp);
+#endif /* #if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_TREE_PREEMPT_RCU) */
 static int rcu_preempt_pending(int cpu);
 static int rcu_preempt_needs_cpu(int cpu);
 static void __cpuinit rcu_preempt_init_percpu_data(int cpu);

kernel/rcutree_trace.c

@@ -155,12 +155,15 @@ static const struct file_operations rcudata_csv_fops = {
 
 static void print_one_rcu_state(struct seq_file *m, struct rcu_state *rsp)
 {
+	long gpnum;
 	int level = 0;
+	int phase;
 	struct rcu_node *rnp;
 
+	gpnum = rsp->gpnum;
 	seq_printf(m, "c=%ld g=%ld s=%d jfq=%ld j=%x "
 		      "nfqs=%lu/nfqsng=%lu(%lu) fqlh=%lu oqlen=%ld\n",
-		   rsp->completed, rsp->gpnum, rsp->signaled,
+		   rsp->completed, gpnum, rsp->signaled,
 		   (long)(rsp->jiffies_force_qs - jiffies),
 		   (int)(jiffies & 0xffff),
 		   rsp->n_force_qs, rsp->n_force_qs_ngp,
@@ -171,8 +174,13 @@ static void print_one_rcu_state(struct seq_file *m, struct rcu_state *rsp)
 			seq_puts(m, "\n");
 			level = rnp->level;
 		}
-		seq_printf(m, "%lx/%lx %d:%d ^%d    ",
+		phase = gpnum & 0x1;
+		seq_printf(m, "%lx/%lx %c%c>%c%c %d:%d ^%d    ",
 			   rnp->qsmask, rnp->qsmaskinit,
+			   "T."[list_empty(&rnp->blocked_tasks[phase])],
+			   "E."[list_empty(&rnp->blocked_tasks[phase + 2])],
+			   "T."[list_empty(&rnp->blocked_tasks[!phase])],
+			   "E."[list_empty(&rnp->blocked_tasks[!phase + 2])],
 			   rnp->grplo, rnp->grphi, rnp->grpnum);
 	}
 	seq_puts(m, "\n");

kernel/sched.c

@@ -10901,6 +10901,7 @@ void synchronize_sched_expedited(void)
 		spin_unlock_irqrestore(&rq->lock, flags);
 	}
 	rcu_expedited_state = RCU_EXPEDITED_STATE_IDLE;
+	synchronize_sched_expedited_count++;
 	mutex_unlock(&rcu_sched_expedited_mutex);
 	put_online_cpus();
 	if (need_full_sync)

kernel/softirq.c

@@ -302,9 +302,9 @@ void irq_exit(void)
 	if (!in_interrupt() && local_softirq_pending())
 		invoke_softirq();
 
+	rcu_irq_exit();
 #ifdef CONFIG_NO_HZ
 	/* Make sure that timer wheel updates are propagated */
-	rcu_irq_exit();
 	if (idle_cpu(smp_processor_id()) && !in_interrupt() && !need_resched())
 		tick_nohz_stop_sched_tick(0);
 #endif

kernel/srcu.c

@@ -49,6 +49,7 @@ int init_srcu_struct(struct srcu_struct *sp)
 	sp->per_cpu_ref = alloc_percpu(struct srcu_struct_array);
 	return (sp->per_cpu_ref ? 0 : -ENOMEM);
 }
+EXPORT_SYMBOL_GPL(init_srcu_struct);
 
 /*
  * srcu_readers_active_idx -- returns approximate number of readers
@@ -97,6 +98,7 @@ void cleanup_srcu_struct(struct srcu_struct *sp)
 	free_percpu(sp->per_cpu_ref);
 	sp->per_cpu_ref = NULL;
 }
+EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
 
 /**
  * srcu_read_lock - register a new reader for an SRCU-protected structure.
@@ -118,6 +120,7 @@ int srcu_read_lock(struct srcu_struct *sp)
 	preempt_enable();
 	return idx;
 }
+EXPORT_SYMBOL_GPL(srcu_read_lock);
 
 /**
  * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
@@ -136,22 +139,12 @@ void srcu_read_unlock(struct srcu_struct *sp, int idx)
 	per_cpu_ptr(sp->per_cpu_ref, smp_processor_id())->c[idx]--;
 	preempt_enable();
 }
+EXPORT_SYMBOL_GPL(srcu_read_unlock);
 
-/**
- * synchronize_srcu - wait for prior SRCU read-side critical-section completion
- * @sp: srcu_struct with which to synchronize.
- *
- * Flip the completed counter, and wait for the old count to drain to zero.
- * As with classic RCU, the updater must use some separate means of
- * synchronizing concurrent updates.  Can block; must be called from
- * process context.
- *
- * Note that it is illegal to call synchornize_srcu() from the corresponding
- * SRCU read-side critical section; doing so will result in deadlock.
- * However, it is perfectly legal to call synchronize_srcu() on one
- * srcu_struct from some other srcu_struct's read-side critical section.
+/*
+ * Helper function for synchronize_srcu() and synchronize_srcu_expedited().
  */
-void synchronize_srcu(struct srcu_struct *sp)
+void __synchronize_srcu(struct srcu_struct *sp, void (*sync_func)(void))
 {
 	int idx;
 
@@ -173,7 +166,7 @@ void synchronize_srcu(struct srcu_struct *sp)
 		return;
 	}
 
-	synchronize_sched();  /* Force memory barrier on all CPUs. */
+	sync_func();  /* Force memory barrier on all CPUs. */
 
 	/*
 	 * The preceding synchronize_sched() ensures that any CPU that
@@ -190,7 +183,7 @@ void synchronize_srcu(struct srcu_struct *sp)
 	idx = sp->completed & 0x1;
 	sp->completed++;
 
-	synchronize_sched();  /* Force memory barrier on all CPUs. */
+	sync_func();  /* Force memory barrier on all CPUs. */
 
 	/*
 	 * At this point, because of the preceding synchronize_sched(),
@@ -203,7 +196,7 @@ void synchronize_srcu(struct srcu_struct *sp)
 	while (srcu_readers_active_idx(sp, idx))
 		schedule_timeout_interruptible(1);
 
-	synchronize_sched();  /* Force memory barrier on all CPUs. */
+	sync_func();  /* Force memory barrier on all CPUs. */
 
 	/*
 	 * The preceding synchronize_sched() forces all srcu_read_unlock()
@@ -236,6 +229,47 @@ void synchronize_srcu(struct srcu_struct *sp)
 	mutex_unlock(&sp->mutex);
 }
 
+/**
+ * synchronize_srcu - wait for prior SRCU read-side critical-section completion
+ * @sp: srcu_struct with which to synchronize.
+ *
+ * Flip the completed counter, and wait for the old count to drain to zero.
+ * As with classic RCU, the updater must use some separate means of
+ * synchronizing concurrent updates.  Can block; must be called from
+ * process context.
+ *
+ * Note that it is illegal to call synchronize_srcu() from the corresponding
+ * SRCU read-side critical section; doing so will result in deadlock.
+ * However, it is perfectly legal to call synchronize_srcu() on one
+ * srcu_struct from some other srcu_struct's read-side critical section.
+ */
+void synchronize_srcu(struct srcu_struct *sp)
+{
+	__synchronize_srcu(sp, synchronize_sched);
+}
+EXPORT_SYMBOL_GPL(synchronize_srcu);
+
+/**
+ * synchronize_srcu_expedited - like synchronize_srcu, but less patient
+ * @sp: srcu_struct with which to synchronize.
+ *
+ * Flip the completed counter, and wait for the old count to drain to zero.
+ * As with classic RCU, the updater must use some separate means of
+ * synchronizing concurrent updates.  Can block; must be called from
+ * process context.
+ *
+ * Note that it is illegal to call synchronize_srcu_expedited()
+ * from the corresponding SRCU read-side critical section; doing so
+ * will result in deadlock.  However, it is perfectly legal to call
+ * synchronize_srcu_expedited() on one srcu_struct from some other
+ * srcu_struct's read-side critical section.
+ */
+void synchronize_srcu_expedited(struct srcu_struct *sp)
+{
+	__synchronize_srcu(sp, synchronize_sched_expedited);
+}
+EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
+
 /**
  * srcu_batches_completed - return batches completed.
  * @sp: srcu_struct on which to report batch completion.
@@ -248,10 +282,4 @@ long srcu_batches_completed(struct srcu_struct *sp)
 {
 	return sp->completed;
 }
-
-EXPORT_SYMBOL_GPL(init_srcu_struct);
-EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
-EXPORT_SYMBOL_GPL(srcu_read_lock);
-EXPORT_SYMBOL_GPL(srcu_read_unlock);
-EXPORT_SYMBOL_GPL(synchronize_srcu);
 EXPORT_SYMBOL_GPL(srcu_batches_completed);

lib/Kconfig.debug

@@ -750,7 +750,7 @@ config RCU_TORTURE_TEST_RUNNABLE
 config RCU_CPU_STALL_DETECTOR
 	bool "Check for stalled CPUs delaying RCU grace periods"
 	depends on TREE_RCU || TREE_PREEMPT_RCU
-	default n
+	default y
 	help
 	  This option causes RCU to printk information on which
 	  CPUs are delaying the current grace period, but only when