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

Pull RCU changes for v3.4 from Ingo Molnar.  The major features of this
series are:

 - making RCU more aggressive about entering dyntick-idle mode in order
   to improve energy efficiency

 - converting a few more call_rcu()s to kfree_rcu()s

 - applying a number of rcutree fixes and cleanups to rcutiny

 - removing CONFIG_SMP #ifdefs from treercu

 - allowing RCU CPU stall times to be set via sysfs

 - adding CPU-stall capability to rcutorture

 - adding more RCU-abuse diagnostics

 - updating documentation

 - fixing yet more issues located by the still-ongoing top-to-bottom
   inspection of RCU, this time with a special focus on the CPU-hotplug
   code path.

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (48 commits)
  rcu: Stop spurious warnings from synchronize_sched_expedited
  rcu: Hold off RCU_FAST_NO_HZ after timer posted
  rcu: Eliminate softirq-mediated RCU_FAST_NO_HZ idle-entry loop
  rcu: Add RCU_NONIDLE() for idle-loop RCU read-side critical sections
  rcu: Allow nesting of rcu_idle_enter() and rcu_idle_exit()
  rcu: Remove redundant check for rcu_head misalignment
  PTR_ERR should be called before its argument is cleared.
  rcu: Convert WARN_ON_ONCE() in rcu_lock_acquire() to lockdep
  rcu: Trace only after NULL-pointer check
  rcu: Call out dangers of expedited RCU primitives
  rcu: Rework detection of use of RCU by offline CPUs
  lockdep: Add CPU-idle/offline warning to lockdep-RCU splat
  rcu: No interrupt disabling for rcu_prepare_for_idle()
  rcu: Move synchronize_sched_expedited() to rcutree.c
  rcu: Check for illegal use of RCU from offlined CPUs
  rcu: Update stall-warning documentation
  rcu: Add CPU-stall capability to rcutorture
  rcu: Make documentation give more realistic rcutorture duration
  rcutorture: Permit holding off CPU-hotplug operations during boot
  rcu: Print scheduling-clock information on RCU CPU stall-warning messages
  ...

11 files changed, 893 insertions, 369 deletions

diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 8889f7dd7c46..ea9ee4518c35 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -4176,7 +4176,13 @@ void lockdep_rcu_suspicious(const char *file, const int line, const char *s)
 	printk("-------------------------------\n");
 	printk("%s:%d %s!\n", file, line, s);
 	printk("\nother info that might help us debug this:\n\n");
-	printk("\nrcu_scheduler_active = %d, debug_locks = %d\n", rcu_scheduler_active, debug_locks);
+	printk("\n%srcu_scheduler_active = %d, debug_locks = %d\n",
+	       !rcu_lockdep_current_cpu_online()
+			? "RCU used illegally from offline CPU!\n"
+			: rcu_is_cpu_idle()
+				? "RCU used illegally from idle CPU!\n"
+				: "",
+	       rcu_scheduler_active, debug_locks);
 
 	/*
 	 * If a CPU is in the RCU-free window in idle (ie: in the section
diff --git a/kernel/rcu.h b/kernel/rcu.h
index aa88baab5f78..8ba99cdc6515 100644
--- a/kernel/rcu.h
+++ b/kernel/rcu.h
@@ -33,8 +33,27 @@
  * Process-level increment to ->dynticks_nesting field.  This allows for
  * architectures that use half-interrupts and half-exceptions from
  * process context.
+ *
+ * DYNTICK_TASK_NEST_MASK defines a field of width DYNTICK_TASK_NEST_WIDTH
+ * that counts the number of process-based reasons why RCU cannot
+ * consider the corresponding CPU to be idle, and DYNTICK_TASK_NEST_VALUE
+ * is the value used to increment or decrement this field.
+ *
+ * The rest of the bits could in principle be used to count interrupts,
+ * but this would mean that a negative-one value in the interrupt
+ * field could incorrectly zero out the DYNTICK_TASK_NEST_MASK field.
+ * We therefore provide a two-bit guard field defined by DYNTICK_TASK_MASK
+ * that is set to DYNTICK_TASK_FLAG upon initial exit from idle.
+ * The DYNTICK_TASK_EXIT_IDLE value is thus the combined value used upon
+ * initial exit from idle.
  */
-#define DYNTICK_TASK_NESTING (LLONG_MAX / 2 - 1)
+#define DYNTICK_TASK_NEST_WIDTH 7
+#define DYNTICK_TASK_NEST_VALUE ((LLONG_MAX >> DYNTICK_TASK_NEST_WIDTH) + 1)
+#define DYNTICK_TASK_NEST_MASK  (LLONG_MAX - DYNTICK_TASK_NEST_VALUE + 1)
+#define DYNTICK_TASK_FLAG	   ((DYNTICK_TASK_NEST_VALUE / 8) * 2)
+#define DYNTICK_TASK_MASK	   ((DYNTICK_TASK_NEST_VALUE / 8) * 3)
+#define DYNTICK_TASK_EXIT_IDLE	   (DYNTICK_TASK_NEST_VALUE + \
+				    DYNTICK_TASK_FLAG)
 
 /*
  * debug_rcu_head_queue()/debug_rcu_head_unqueue() are used internally
@@ -50,7 +69,6 @@ extern struct debug_obj_descr rcuhead_debug_descr;
 
 static inline void debug_rcu_head_queue(struct rcu_head *head)
 {
-	WARN_ON_ONCE((unsigned long)head & 0x3);
 	debug_object_activate(head, &rcuhead_debug_descr);
 	debug_object_active_state(head, &rcuhead_debug_descr,
 				  STATE_RCU_HEAD_READY,
@@ -76,16 +94,18 @@ static inline void debug_rcu_head_unqueue(struct rcu_head *head)
 
 extern void kfree(const void *);
 
-static inline void __rcu_reclaim(char *rn, struct rcu_head *head)
+static inline bool __rcu_reclaim(char *rn, struct rcu_head *head)
 {
 	unsigned long offset = (unsigned long)head->func;
 
 	if (__is_kfree_rcu_offset(offset)) {
 		RCU_TRACE(trace_rcu_invoke_kfree_callback(rn, head, offset));
 		kfree((void *)head - offset);
+		return 1;
 	} else {
 		RCU_TRACE(trace_rcu_invoke_callback(rn, head));
 		head->func(head);
+		return 0;
 	}
 }
 
diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index 2bc4e135ff23..a86f1741cc27 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -88,6 +88,9 @@ EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
  * section.
  *
  * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
+ *
+ * Note that rcu_read_lock() is disallowed if the CPU is either idle or
+ * offline from an RCU perspective, so check for those as well.
  */
 int rcu_read_lock_bh_held(void)
 {
@@ -95,6 +98,8 @@ int rcu_read_lock_bh_held(void)
 		return 1;
 	if (rcu_is_cpu_idle())
 		return 0;
+	if (!rcu_lockdep_current_cpu_online())
+		return 0;
 	return in_softirq() || irqs_disabled();
 }
 EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
index 977296dca0a4..37a5444204d2 100644
--- a/kernel/rcutiny.c
+++ b/kernel/rcutiny.c
@@ -53,7 +53,7 @@ static void __call_rcu(struct rcu_head *head,
 
 #include "rcutiny_plugin.h"
 
-static long long rcu_dynticks_nesting = DYNTICK_TASK_NESTING;
+static long long rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
 
 /* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcutree.c. */
 static void rcu_idle_enter_common(long long oldval)
@@ -88,10 +88,16 @@ void rcu_idle_enter(void)
 
 	local_irq_save(flags);
 	oldval = rcu_dynticks_nesting;
-	rcu_dynticks_nesting = 0;
+	WARN_ON_ONCE((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) == 0);
+	if ((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) ==
+	    DYNTICK_TASK_NEST_VALUE)
+		rcu_dynticks_nesting = 0;
+	else
+		rcu_dynticks_nesting  -= DYNTICK_TASK_NEST_VALUE;
 	rcu_idle_enter_common(oldval);
 	local_irq_restore(flags);
 }
+EXPORT_SYMBOL_GPL(rcu_idle_enter);
 
 /*
  * Exit an interrupt handler towards idle.
@@ -140,11 +146,15 @@ void rcu_idle_exit(void)
 
 	local_irq_save(flags);
 	oldval = rcu_dynticks_nesting;
-	WARN_ON_ONCE(oldval != 0);
-	rcu_dynticks_nesting = DYNTICK_TASK_NESTING;
+	WARN_ON_ONCE(rcu_dynticks_nesting < 0);
+	if (rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK)
+		rcu_dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
+	else
+		rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
 	rcu_idle_exit_common(oldval);
 	local_irq_restore(flags);
 }
+EXPORT_SYMBOL_GPL(rcu_idle_exit);
 
 /*
  * Enter an interrupt handler, moving away from idle.
@@ -258,7 +268,7 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 
 	/* If no RCU callbacks ready to invoke, just return. */
 	if (&rcp->rcucblist == rcp->donetail) {
-		RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, -1));
+		RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, 0, -1));
 		RCU_TRACE(trace_rcu_batch_end(rcp->name, 0,
 					      ACCESS_ONCE(rcp->rcucblist),
 					      need_resched(),
@@ -269,7 +279,7 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 
 	/* Move the ready-to-invoke callbacks to a local list. */
 	local_irq_save(flags);
-	RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, -1));
+	RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1));
 	list = rcp->rcucblist;
 	rcp->rcucblist = *rcp->donetail;
 	*rcp->donetail = NULL;
@@ -319,6 +329,10 @@ static void rcu_process_callbacks(struct softirq_action *unused)
  */
 void synchronize_sched(void)
 {
+	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_sched() in RCU read-side critical section");
 	cond_resched();
 }
 EXPORT_SYMBOL_GPL(synchronize_sched);
diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
index 9cb1ae4aabdd..22ecea0dfb62 100644
--- a/kernel/rcutiny_plugin.h
+++ b/kernel/rcutiny_plugin.h
@@ -132,6 +132,7 @@ static struct rcu_preempt_ctrlblk rcu_preempt_ctrlblk = {
 	RCU_TRACE(.rcb.name = "rcu_preempt")
 };
 
+static void rcu_read_unlock_special(struct task_struct *t);
 static int rcu_preempted_readers_exp(void);
 static void rcu_report_exp_done(void);
 
@@ -146,6 +147,16 @@ static int rcu_cpu_blocking_cur_gp(void)
 /*
  * Check for a running RCU reader.  Because there is only one CPU,
  * there can be but one running RCU reader at a time.  ;-)
+ *
+ * Returns zero if there are no running readers.  Returns a positive
+ * number if there is at least one reader within its RCU read-side
+ * critical section.  Returns a negative number if an outermost reader
+ * is in the midst of exiting from its RCU read-side critical section
+ *
+ * Returns zero if there are no running readers.  Returns a positive
+ * number if there is at least one reader within its RCU read-side
+ * critical section.  Returns a negative number if an outermost reader
+ * is in the midst of exiting from its RCU read-side critical section.
  */
 static int rcu_preempt_running_reader(void)
 {
@@ -307,7 +318,6 @@ static int rcu_boost(void)
 	t = container_of(tb, struct task_struct, rcu_node_entry);
 	rt_mutex_init_proxy_locked(&mtx, t);
 	t->rcu_boost_mutex = &mtx;
-	t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BOOSTED;
 	raw_local_irq_restore(flags);
 	rt_mutex_lock(&mtx);
 	rt_mutex_unlock(&mtx);  /* Keep lockdep happy. */
@@ -475,7 +485,7 @@ void rcu_preempt_note_context_switch(void)
 	unsigned long flags;
 
 	local_irq_save(flags); /* must exclude scheduler_tick(). */
-	if (rcu_preempt_running_reader() &&
+	if (rcu_preempt_running_reader() > 0 &&
 	    (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
 
 		/* Possibly blocking in an RCU read-side critical section. */
@@ -494,6 +504,13 @@ void rcu_preempt_note_context_switch(void)
 		list_add(&t->rcu_node_entry, &rcu_preempt_ctrlblk.blkd_tasks);
 		if (rcu_cpu_blocking_cur_gp())
 			rcu_preempt_ctrlblk.gp_tasks = &t->rcu_node_entry;
+	} else if (rcu_preempt_running_reader() < 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);
 	}
 
 	/*
@@ -526,12 +543,15 @@ EXPORT_SYMBOL_GPL(__rcu_read_lock);
  * notify RCU core processing or task having blocked during the RCU
  * read-side critical section.
  */
-static void rcu_read_unlock_special(struct task_struct *t)
+static noinline void rcu_read_unlock_special(struct task_struct *t)
 {
 	int empty;
 	int empty_exp;
 	unsigned long flags;
 	struct list_head *np;
+#ifdef CONFIG_RCU_BOOST
+	struct rt_mutex *rbmp = NULL;
+#endif /* #ifdef CONFIG_RCU_BOOST */
 	int special;
 
 	/*
@@ -552,7 +572,7 @@ static void rcu_read_unlock_special(struct task_struct *t)
 		rcu_preempt_cpu_qs();
 
 	/* Hardware IRQ handlers cannot block. */
-	if (in_irq()) {
+	if (in_irq() || in_serving_softirq()) {
 		local_irq_restore(flags);
 		return;
 	}
@@ -597,10 +617,10 @@ static void rcu_read_unlock_special(struct task_struct *t)
 	}
 #ifdef CONFIG_RCU_BOOST
 	/* Unboost self if was boosted. */
-	if (special & RCU_READ_UNLOCK_BOOSTED) {
-		t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BOOSTED;
-		rt_mutex_unlock(t->rcu_boost_mutex);
+	if (t->rcu_boost_mutex != NULL) {
+		rbmp = t->rcu_boost_mutex;
 		t->rcu_boost_mutex = NULL;
+		rt_mutex_unlock(rbmp);
 	}
 #endif /* #ifdef CONFIG_RCU_BOOST */
 	local_irq_restore(flags);
@@ -618,13 +638,22 @@ void __rcu_read_unlock(void)
 	struct task_struct *t = current;
 
 	barrier();  /* needed if we ever invoke rcu_read_unlock in rcutiny.c */
-	--t->rcu_read_lock_nesting;
-	barrier();  /* decrement before load of ->rcu_read_unlock_special */
-	if (t->rcu_read_lock_nesting == 0 &&
-	    unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
-		rcu_read_unlock_special(t);
+	if (t->rcu_read_lock_nesting != 1)
+		--t->rcu_read_lock_nesting;
+	else {
+		t->rcu_read_lock_nesting = INT_MIN;
+		barrier();  /* assign before ->rcu_read_unlock_special load */
+		if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
+			rcu_read_unlock_special(t);
+		barrier();  /* ->rcu_read_unlock_special load before assign */
+		t->rcu_read_lock_nesting = 0;
+	}
 #ifdef CONFIG_PROVE_LOCKING
-	WARN_ON_ONCE(t->rcu_read_lock_nesting < 0);
+	{
+		int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting);
+
+		WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
+	}
 #endif /* #ifdef CONFIG_PROVE_LOCKING */
 }
 EXPORT_SYMBOL_GPL(__rcu_read_unlock);
@@ -649,7 +678,7 @@ static void rcu_preempt_check_callbacks(void)
 		invoke_rcu_callbacks();
 	if (rcu_preempt_gp_in_progress() &&
 	    rcu_cpu_blocking_cur_gp() &&
-	    rcu_preempt_running_reader())
+	    rcu_preempt_running_reader() > 0)
 		t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
 }
 
@@ -706,6 +735,11 @@ EXPORT_SYMBOL_GPL(call_rcu);
  */
 void synchronize_rcu(void)
 {
+	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");
+
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	if (!rcu_scheduler_active)
 		return;
@@ -882,7 +916,8 @@ static void rcu_preempt_process_callbacks(void)
 static void invoke_rcu_callbacks(void)
 {
 	have_rcu_kthread_work = 1;
-	wake_up(&rcu_kthread_wq);
+	if (rcu_kthread_task != NULL)
+		wake_up(&rcu_kthread_wq);
 }
 
 #ifdef CONFIG_RCU_TRACE
@@ -943,12 +978,16 @@ early_initcall(rcu_spawn_kthreads);
 
 #else /* #ifdef CONFIG_RCU_BOOST */
 
+/* Hold off callback invocation until early_initcall() time. */
+static int rcu_scheduler_fully_active __read_mostly;
+
 /*
  * Start up softirq processing of callbacks.
  */
 void invoke_rcu_callbacks(void)
 {
-	raise_softirq(RCU_SOFTIRQ);
+	if (rcu_scheduler_fully_active)
+		raise_softirq(RCU_SOFTIRQ);
 }
 
 #ifdef CONFIG_RCU_TRACE
@@ -963,10 +1002,14 @@ static bool rcu_is_callbacks_kthread(void)
 
 #endif /* #ifdef CONFIG_RCU_TRACE */
 
-void rcu_init(void)
+static int __init rcu_scheduler_really_started(void)
 {
+	rcu_scheduler_fully_active = 1;
 	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
+	raise_softirq(RCU_SOFTIRQ);  /* Invoke any callbacks from early boot. */
+	return 0;
 }
+early_initcall(rcu_scheduler_really_started);
 
 #endif /* #else #ifdef CONFIG_RCU_BOOST */
 
diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c
index a58ac285fc69..a89b381a8c6e 100644
--- a/kernel/rcutorture.c
+++ b/kernel/rcutorture.c
@@ -65,7 +65,10 @@ static int fqs_duration;	/* Duration of bursts (us), 0 to disable. */
 static int fqs_holdoff;		/* Hold time within burst (us). */
 static int fqs_stutter = 3;	/* Wait time between bursts (s). */
 static int onoff_interval;	/* Wait time between CPU hotplugs, 0=disable. */
+static int onoff_holdoff;	/* Seconds after boot before CPU hotplugs. */
 static int shutdown_secs;	/* Shutdown time (s).  <=0 for no shutdown. */
+static int stall_cpu;		/* CPU-stall duration (s).  0 for no stall. */
+static int stall_cpu_holdoff = 10; /* Time to wait until stall (s).  */
 static int test_boost = 1;	/* Test RCU prio boost: 0=no, 1=maybe, 2=yes. */
 static int test_boost_interval = 7; /* Interval between boost tests, seconds. */
 static int test_boost_duration = 4; /* Duration of each boost test, seconds. */
@@ -95,8 +98,14 @@ module_param(fqs_stutter, int, 0444);
 MODULE_PARM_DESC(fqs_stutter, "Wait time between fqs bursts (s)");
 module_param(onoff_interval, int, 0444);
 MODULE_PARM_DESC(onoff_interval, "Time between CPU hotplugs (s), 0=disable");
+module_param(onoff_holdoff, int, 0444);
+MODULE_PARM_DESC(onoff_holdoff, "Time after boot before CPU hotplugs (s)");
 module_param(shutdown_secs, int, 0444);
 MODULE_PARM_DESC(shutdown_secs, "Shutdown time (s), zero to disable.");
+module_param(stall_cpu, int, 0444);
+MODULE_PARM_DESC(stall_cpu, "Stall duration (s), zero to disable.");
+module_param(stall_cpu_holdoff, int, 0444);
+MODULE_PARM_DESC(stall_cpu_holdoff, "Time to wait before starting stall (s).");
 module_param(test_boost, int, 0444);
 MODULE_PARM_DESC(test_boost, "Test RCU prio boost: 0=no, 1=maybe, 2=yes.");
 module_param(test_boost_interval, int, 0444);
@@ -129,6 +138,7 @@ static struct task_struct *shutdown_task;
 #ifdef CONFIG_HOTPLUG_CPU
 static struct task_struct *onoff_task;
 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
+static struct task_struct *stall_task;
 
 #define RCU_TORTURE_PIPE_LEN 10
 
@@ -990,12 +1000,12 @@ static void rcu_torture_timer(unsigned long unused)
 				  rcu_read_lock_bh_held() ||
 				  rcu_read_lock_sched_held() ||
 				  srcu_read_lock_held(&srcu_ctl));
-	do_trace_rcu_torture_read(cur_ops->name, &p->rtort_rcu);
 	if (p == NULL) {
 		/* Leave because rcu_torture_writer is not yet underway */
 		cur_ops->readunlock(idx);
 		return;
 	}
+	do_trace_rcu_torture_read(cur_ops->name, &p->rtort_rcu);
 	if (p->rtort_mbtest == 0)
 		atomic_inc(&n_rcu_torture_mberror);
 	spin_lock(&rand_lock);
@@ -1053,13 +1063,13 @@ rcu_torture_reader(void *arg)
 					  rcu_read_lock_bh_held() ||
 					  rcu_read_lock_sched_held() ||
 					  srcu_read_lock_held(&srcu_ctl));
-		do_trace_rcu_torture_read(cur_ops->name, &p->rtort_rcu);
 		if (p == NULL) {
 			/* Wait for rcu_torture_writer to get underway */
 			cur_ops->readunlock(idx);
 			schedule_timeout_interruptible(HZ);
 			continue;
 		}
+		do_trace_rcu_torture_read(cur_ops->name, &p->rtort_rcu);
 		if (p->rtort_mbtest == 0)
 			atomic_inc(&n_rcu_torture_mberror);
 		cur_ops->read_delay(&rand);
@@ -1300,13 +1310,13 @@ rcu_torture_print_module_parms(struct rcu_torture_ops *cur_ops, char *tag)
 		"fqs_duration=%d fqs_holdoff=%d fqs_stutter=%d "
 		"test_boost=%d/%d test_boost_interval=%d "
 		"test_boost_duration=%d shutdown_secs=%d "
-		"onoff_interval=%d\n",
+		"onoff_interval=%d onoff_holdoff=%d\n",
 		torture_type, tag, nrealreaders, nfakewriters,
 		stat_interval, verbose, test_no_idle_hz, shuffle_interval,
 		stutter, irqreader, fqs_duration, fqs_holdoff, fqs_stutter,
 		test_boost, cur_ops->can_boost,
 		test_boost_interval, test_boost_duration, shutdown_secs,
-		onoff_interval);
+		onoff_interval, onoff_holdoff);
 }
 
 static struct notifier_block rcutorture_shutdown_nb = {
@@ -1410,6 +1420,11 @@ rcu_torture_onoff(void *arg)
 	for_each_online_cpu(cpu)
 		maxcpu = cpu;
 	WARN_ON(maxcpu < 0);
+	if (onoff_holdoff > 0) {
+		VERBOSE_PRINTK_STRING("rcu_torture_onoff begin holdoff");
+		schedule_timeout_interruptible(onoff_holdoff * HZ);
+		VERBOSE_PRINTK_STRING("rcu_torture_onoff end holdoff");
+	}
 	while (!kthread_should_stop()) {
 		cpu = (rcu_random(&rand) >> 4) % (maxcpu + 1);
 		if (cpu_online(cpu) && cpu_is_hotpluggable(cpu)) {
@@ -1450,12 +1465,15 @@ rcu_torture_onoff(void *arg)
 static int __cpuinit
 rcu_torture_onoff_init(void)
 {
+	int ret;
+
 	if (onoff_interval <= 0)
 		return 0;
 	onoff_task = kthread_run(rcu_torture_onoff, NULL, "rcu_torture_onoff");
 	if (IS_ERR(onoff_task)) {
+		ret = PTR_ERR(onoff_task);
 		onoff_task = NULL;
-		return PTR_ERR(onoff_task);
+		return ret;
 	}
 	return 0;
 }
@@ -1481,6 +1499,63 @@ static void rcu_torture_onoff_cleanup(void)
 
 #endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
 
+/*
+ * CPU-stall kthread.  It waits as specified by stall_cpu_holdoff, then
+ * induces a CPU stall for the time specified by stall_cpu.
+ */
+static int __cpuinit rcu_torture_stall(void *args)
+{
+	unsigned long stop_at;
+
+	VERBOSE_PRINTK_STRING("rcu_torture_stall task started");
+	if (stall_cpu_holdoff > 0) {
+		VERBOSE_PRINTK_STRING("rcu_torture_stall begin holdoff");
+		schedule_timeout_interruptible(stall_cpu_holdoff * HZ);
+		VERBOSE_PRINTK_STRING("rcu_torture_stall end holdoff");
+	}
+	if (!kthread_should_stop()) {
+		stop_at = get_seconds() + stall_cpu;
+		/* RCU CPU stall is expected behavior in following code. */
+		printk(KERN_ALERT "rcu_torture_stall start.\n");
+		rcu_read_lock();
+		preempt_disable();
+		while (ULONG_CMP_LT(get_seconds(), stop_at))
+			continue;  /* Induce RCU CPU stall warning. */
+		preempt_enable();
+		rcu_read_unlock();
+		printk(KERN_ALERT "rcu_torture_stall end.\n");
+	}
+	rcutorture_shutdown_absorb("rcu_torture_stall");
+	while (!kthread_should_stop())
+		schedule_timeout_interruptible(10 * HZ);
+	return 0;
+}
+
+/* Spawn CPU-stall kthread, if stall_cpu specified. */
+static int __init rcu_torture_stall_init(void)
+{
+	int ret;
+
+	if (stall_cpu <= 0)
+		return 0;
+	stall_task = kthread_run(rcu_torture_stall, NULL, "rcu_torture_stall");
+	if (IS_ERR(stall_task)) {
+		ret = PTR_ERR(stall_task);
+		stall_task = NULL;
+		return ret;
+	}
+	return 0;
+}
+
+/* Clean up after the CPU-stall kthread, if one was spawned. */
+static void rcu_torture_stall_cleanup(void)
+{
+	if (stall_task == NULL)
+		return;
+	VERBOSE_PRINTK_STRING("Stopping rcu_torture_stall_task.");
+	kthread_stop(stall_task);
+}
+
 static int rcutorture_cpu_notify(struct notifier_block *self,
 				 unsigned long action, void *hcpu)
 {
@@ -1523,6 +1598,7 @@ rcu_torture_cleanup(void)
 	fullstop = FULLSTOP_RMMOD;
 	mutex_unlock(&fullstop_mutex);
 	unregister_reboot_notifier(&rcutorture_shutdown_nb);
+	rcu_torture_stall_cleanup();
 	if (stutter_task) {
 		VERBOSE_PRINTK_STRING("Stopping rcu_torture_stutter task");
 		kthread_stop(stutter_task);
@@ -1602,6 +1678,10 @@ rcu_torture_cleanup(void)
 		cur_ops->cleanup();
 	if (atomic_read(&n_rcu_torture_error))
 		rcu_torture_print_module_parms(cur_ops, "End of test: FAILURE");
+	else if (n_online_successes != n_online_attempts ||
+		 n_offline_successes != n_offline_attempts)
+		rcu_torture_print_module_parms(cur_ops,
+					       "End of test: RCU_HOTPLUG");
 	else
 		rcu_torture_print_module_parms(cur_ops, "End of test: SUCCESS");
 }
@@ -1819,6 +1899,7 @@ rcu_torture_init(void)
 	}
 	rcu_torture_onoff_init();
 	register_reboot_notifier(&rcutorture_shutdown_nb);
+	rcu_torture_stall_init();
 	rcutorture_record_test_transition();
 	mutex_unlock(&fullstop_mutex);
 	return 0;
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 6c4a6722abfd..1050d6d3922c 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -50,6 +50,8 @@
 #include <linux/wait.h>
 #include <linux/kthread.h>
 #include <linux/prefetch.h>
+#include <linux/delay.h>
+#include <linux/stop_machine.h>
 
 #include "rcutree.h"
 #include <trace/events/rcu.h>
@@ -196,7 +198,7 @@ void rcu_note_context_switch(int cpu)
 EXPORT_SYMBOL_GPL(rcu_note_context_switch);
 
 DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
-	.dynticks_nesting = DYNTICK_TASK_NESTING,
+	.dynticks_nesting = DYNTICK_TASK_EXIT_IDLE,
 	.dynticks = ATOMIC_INIT(1),
 };
 
@@ -208,8 +210,11 @@ module_param(blimit, int, 0);
 module_param(qhimark, int, 0);
 module_param(qlowmark, int, 0);
 
-int rcu_cpu_stall_suppress __read_mostly;
+int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */
+int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;
+
 module_param(rcu_cpu_stall_suppress, int, 0644);
+module_param(rcu_cpu_stall_timeout, int, 0644);
 
 static void force_quiescent_state(struct rcu_state *rsp, int relaxed);
 static int rcu_pending(int cpu);
@@ -301,8 +306,6 @@ static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
 	return &rsp->node[0];
 }
 
-#ifdef CONFIG_SMP
-
 /*
  * If the specified CPU is offline, tell the caller that it is in
  * a quiescent state.  Otherwise, whack it with a reschedule IPI.
@@ -317,30 +320,21 @@ static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
 static int rcu_implicit_offline_qs(struct rcu_data *rdp)
 {
 	/*
-	 * If the CPU is offline, it is in a quiescent state.  We can
-	 * trust its state not to change because interrupts are disabled.
+	 * If the CPU is offline for more than a jiffy, it is in a quiescent
+	 * state.  We can trust its state not to change because interrupts
+	 * are disabled.  The reason for the jiffy's worth of slack is to
+	 * handle CPUs initializing on the way up and finding their way
+	 * to the idle loop on the way down.
 	 */
-	if (cpu_is_offline(rdp->cpu)) {
+	if (cpu_is_offline(rdp->cpu) &&
+	    ULONG_CMP_LT(rdp->rsp->gp_start + 2, jiffies)) {
 		trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, "ofl");
 		rdp->offline_fqs++;
 		return 1;
 	}
-
-	/*
-	 * The CPU is online, so send it a reschedule IPI.  This forces
-	 * it through the scheduler, and (inefficiently) also handles cases
-	 * where idle loops fail to inform RCU about the CPU being idle.
-	 */
-	if (rdp->cpu != smp_processor_id())
-		smp_send_reschedule(rdp->cpu);
-	else
-		set_need_resched();
-	rdp->resched_ipi++;
 	return 0;
 }
 
-#endif /* #ifdef CONFIG_SMP */
-
 /*
  * rcu_idle_enter_common - inform RCU that current CPU is moving towards idle
  *
@@ -366,6 +360,17 @@ static void rcu_idle_enter_common(struct rcu_dynticks *rdtp, long long oldval)
 	atomic_inc(&rdtp->dynticks);
 	smp_mb__after_atomic_inc();  /* Force ordering with next sojourn. */
 	WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
+
+	/*
+	 * The idle task is not permitted to enter the idle loop while
+	 * in an RCU read-side critical section.
+	 */
+	rcu_lockdep_assert(!lock_is_held(&rcu_lock_map),
+			   "Illegal idle entry in RCU read-side critical section.");
+	rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map),
+			   "Illegal idle entry in RCU-bh read-side critical section.");
+	rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map),
+			   "Illegal idle entry in RCU-sched read-side critical section.");
 }
 
 /**
@@ -389,10 +394,15 @@ void rcu_idle_enter(void)
 	local_irq_save(flags);
 	rdtp = &__get_cpu_var(rcu_dynticks);
 	oldval = rdtp->dynticks_nesting;
-	rdtp->dynticks_nesting = 0;
+	WARN_ON_ONCE((oldval & DYNTICK_TASK_NEST_MASK) == 0);
+	if ((oldval & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE)
+		rdtp->dynticks_nesting = 0;
+	else
+		rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE;
 	rcu_idle_enter_common(rdtp, oldval);
 	local_irq_restore(flags);
 }
+EXPORT_SYMBOL_GPL(rcu_idle_enter);
 
 /**
  * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
@@ -462,7 +472,7 @@ static void rcu_idle_exit_common(struct rcu_dynticks *rdtp, long long oldval)
  * Exit idle mode, in other words, -enter- the mode in which RCU
  * read-side critical sections can occur.
  *
- * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NESTING to
+ * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST to
  * allow for the possibility of usermode upcalls messing up our count
  * of interrupt nesting level during the busy period that is just
  * now starting.
@@ -476,11 +486,15 @@ void rcu_idle_exit(void)
 	local_irq_save(flags);
 	rdtp = &__get_cpu_var(rcu_dynticks);
 	oldval = rdtp->dynticks_nesting;
-	WARN_ON_ONCE(oldval != 0);
-	rdtp->dynticks_nesting = DYNTICK_TASK_NESTING;
+	WARN_ON_ONCE(oldval < 0);
+	if (oldval & DYNTICK_TASK_NEST_MASK)
+		rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
+	else
+		rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
 	rcu_idle_exit_common(rdtp, oldval);
 	local_irq_restore(flags);
 }
+EXPORT_SYMBOL_GPL(rcu_idle_exit);
 
 /**
  * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
@@ -581,6 +595,49 @@ int rcu_is_cpu_idle(void)
 }
 EXPORT_SYMBOL(rcu_is_cpu_idle);
 
+#ifdef CONFIG_HOTPLUG_CPU
+
+/*
+ * Is the current CPU online?  Disable preemption to avoid false positives
+ * that could otherwise happen due to the current CPU number being sampled,
+ * this task being preempted, its old CPU being taken offline, resuming
+ * on some other CPU, then determining that its old CPU is now offline.
+ * It is OK to use RCU on an offline processor during initial boot, hence
+ * the check for rcu_scheduler_fully_active.  Note also that it is OK
+ * for a CPU coming online to use RCU for one jiffy prior to marking itself
+ * online in the cpu_online_mask.  Similarly, it is OK for a CPU going
+ * offline to continue to use RCU for one jiffy after marking itself
+ * offline in the cpu_online_mask.  This leniency is necessary given the
+ * non-atomic nature of the online and offline processing, for example,
+ * the fact that a CPU enters the scheduler after completing the CPU_DYING
+ * notifiers.
+ *
+ * This is also why RCU internally marks CPUs online during the
+ * CPU_UP_PREPARE phase and offline during the CPU_DEAD phase.
+ *
+ * Disable checking if in an NMI handler because we cannot safely report
+ * errors from NMI handlers anyway.
+ */
+bool rcu_lockdep_current_cpu_online(void)
+{
+	struct rcu_data *rdp;
+	struct rcu_node *rnp;
+	bool ret;
+
+	if (in_nmi())
+		return 1;
+	preempt_disable();
+	rdp = &__get_cpu_var(rcu_sched_data);
+	rnp = rdp->mynode;
+	ret = (rdp->grpmask & rnp->qsmaskinit) ||
+	      !rcu_scheduler_fully_active;
+	preempt_enable();
+	return ret;
+}
+EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
+
+#endif /* #ifdef CONFIG_HOTPLUG_CPU */
+
 #endif /* #ifdef CONFIG_PROVE_RCU */
 
 /**
@@ -595,8 +652,6 @@ int rcu_is_cpu_rrupt_from_idle(void)
 	return __get_cpu_var(rcu_dynticks).dynticks_nesting <= 1;
 }
 
-#ifdef CONFIG_SMP
-
 /*
  * Snapshot the specified CPU's dynticks counter so that we can later
  * credit them with an implicit quiescent state.  Return 1 if this CPU
@@ -640,12 +695,28 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
 	return rcu_implicit_offline_qs(rdp);
 }
 
-#endif /* #ifdef CONFIG_SMP */
+static int jiffies_till_stall_check(void)
+{
+	int till_stall_check = ACCESS_ONCE(rcu_cpu_stall_timeout);
+
+	/*
+	 * Limit check must be consistent with the Kconfig limits
+	 * for CONFIG_RCU_CPU_STALL_TIMEOUT.
+	 */
+	if (till_stall_check < 3) {
+		ACCESS_ONCE(rcu_cpu_stall_timeout) = 3;
+		till_stall_check = 3;
+	} else if (till_stall_check > 300) {
+		ACCESS_ONCE(rcu_cpu_stall_timeout) = 300;
+		till_stall_check = 300;
+	}
+	return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;
+}
 
 static void record_gp_stall_check_time(struct rcu_state *rsp)
 {
 	rsp->gp_start = jiffies;
-	rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_CHECK;
+	rsp->jiffies_stall = jiffies + jiffies_till_stall_check();
 }
 
 static void print_other_cpu_stall(struct rcu_state *rsp)
@@ -664,13 +735,7 @@ static void print_other_cpu_stall(struct rcu_state *rsp)
 		raw_spin_unlock_irqrestore(&rnp->lock, flags);
 		return;
 	}
-	rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_RECHECK;
-
-	/*
-	 * Now rat on any tasks that got kicked up to the root rcu_node
-	 * due to CPU offlining.
-	 */
-	ndetected = rcu_print_task_stall(rnp);
+	rsp->jiffies_stall = jiffies + 3 * jiffies_till_stall_check() + 3;
 	raw_spin_unlock_irqrestore(&rnp->lock, flags);
 
 	/*
@@ -678,8 +743,9 @@ static void print_other_cpu_stall(struct rcu_state *rsp)
 	 * See Documentation/RCU/stallwarn.txt for info on how to debug
 	 * RCU CPU stall warnings.
 	 */
-	printk(KERN_ERR "INFO: %s detected stalls on CPUs/tasks: {",
+	printk(KERN_ERR "INFO: %s detected stalls on CPUs/tasks:",
 	       rsp->name);
+	print_cpu_stall_info_begin();
 	rcu_for_each_leaf_node(rsp, rnp) {
 		raw_spin_lock_irqsave(&rnp->lock, flags);
 		ndetected += rcu_print_task_stall(rnp);
@@ -688,11 +754,22 @@ static void print_other_cpu_stall(struct rcu_state *rsp)
 			continue;
 		for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
 			if (rnp->qsmask & (1UL << cpu)) {
-				printk(" %d", rnp->grplo + cpu);
+				print_cpu_stall_info(rsp, rnp->grplo + cpu);
 				ndetected++;
 			}
 	}
-	printk("} (detected by %d, t=%ld jiffies)\n",
+
+	/*
+	 * Now rat on any tasks that got kicked up to the root rcu_node
+	 * due to CPU offlining.
+	 */
+	rnp = rcu_get_root(rsp);
+	raw_spin_lock_irqsave(&rnp->lock, flags);
+	ndetected = rcu_print_task_stall(rnp);
+	raw_spin_unlock_irqrestore(&rnp->lock, flags);
+
+	print_cpu_stall_info_end();
+	printk(KERN_CONT "(detected by %d, t=%ld jiffies)\n",
 	       smp_processor_id(), (long)(jiffies - rsp->gp_start));
 	if (ndetected == 0)
 		printk(KERN_ERR "INFO: Stall ended before state dump start\n");
@@ -716,15 +793,18 @@ static void print_cpu_stall(struct rcu_state *rsp)
 	 * See Documentation/RCU/stallwarn.txt for info on how to debug
 	 * RCU CPU stall warnings.
 	 */
-	printk(KERN_ERR "INFO: %s detected stall on CPU %d (t=%lu jiffies)\n",
-	       rsp->name, smp_processor_id(), jiffies - rsp->gp_start);
+	printk(KERN_ERR "INFO: %s self-detected stall on CPU", rsp->name);
+	print_cpu_stall_info_begin();
+	print_cpu_stall_info(rsp, smp_processor_id());
+	print_cpu_stall_info_end();
+	printk(KERN_CONT " (t=%lu jiffies)\n", jiffies - rsp->gp_start);
 	if (!trigger_all_cpu_backtrace())
 		dump_stack();
 
 	raw_spin_lock_irqsave(&rnp->lock, flags);
 	if (ULONG_CMP_GE(jiffies, rsp->jiffies_stall))
-		rsp->jiffies_stall =
-			jiffies + RCU_SECONDS_TILL_STALL_RECHECK;
+		rsp->jiffies_stall = jiffies +
+				     3 * jiffies_till_stall_check() + 3;
 	raw_spin_unlock_irqrestore(&rnp->lock, flags);
 
 	set_need_resched();  /* kick ourselves to get things going. */
@@ -807,6 +887,7 @@ static void __note_new_gpnum(struct rcu_state *rsp, struct rcu_node *rnp, struct
 			rdp->passed_quiesce = 0