Merge branch 'rcu/next' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into core/rcu

Pull the v3.18 RCU changes from Paul E. McKenney:

"
  * Update RCU documentation.  These were posted to LKML at
    https://lkml.org/lkml/2014/8/28/378.

  * Miscellaneous fixes.  These were posted to LKML at
    https://lkml.org/lkml/2014/8/28/386.  An additional fix that
    eliminates a documented (but now inconvenient) deadlock between
    RCU hotplug and expedited grace periods was posted at
    https://lkml.org/lkml/2014/8/28/573.

  * Changes related to No-CBs CPUs and NO_HZ_FULL.  These were posted
    to LKML at https://lkml.org/lkml/2014/8/28/412.

  * Torture-test updates.  These were posted to LKML at
    https://lkml.org/lkml/2014/8/28/546 and at
    https://lkml.org/lkml/2014/9/11/1114.

  * RCU-tasks implementation.  These were posted to LKML at
    https://lkml.org/lkml/2014/8/28/540.
"

Signed-off-by: Ingo Molnar <mingo@kernel.org>

12 files changed, 1272 insertions, 362 deletions

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 81e2a388a0f6..356450f09c1f 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -79,6 +79,8 @@ static struct {
 
 /* Lockdep annotations for get/put_online_cpus() and cpu_hotplug_begin/end() */
 #define cpuhp_lock_acquire_read() lock_map_acquire_read(&cpu_hotplug.dep_map)
+#define cpuhp_lock_acquire_tryread() \
+				  lock_map_acquire_tryread(&cpu_hotplug.dep_map)
 #define cpuhp_lock_acquire()      lock_map_acquire(&cpu_hotplug.dep_map)
 #define cpuhp_lock_release()      lock_map_release(&cpu_hotplug.dep_map)
 
@@ -91,10 +93,22 @@ void get_online_cpus(void)
 	mutex_lock(&cpu_hotplug.lock);
 	cpu_hotplug.refcount++;
 	mutex_unlock(&cpu_hotplug.lock);
-
 }
 EXPORT_SYMBOL_GPL(get_online_cpus);
 
+bool try_get_online_cpus(void)
+{
+	if (cpu_hotplug.active_writer == current)
+		return true;
+	if (!mutex_trylock(&cpu_hotplug.lock))
+		return false;
+	cpuhp_lock_acquire_tryread();
+	cpu_hotplug.refcount++;
+	mutex_unlock(&cpu_hotplug.lock);
+	return true;
+}
+EXPORT_SYMBOL_GPL(try_get_online_cpus);
+
 void put_online_cpus(void)
 {
 	if (cpu_hotplug.active_writer == current)
diff --git a/kernel/exit.c b/kernel/exit.c
index 32c58f7433a3..d13f2eec4bb8 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -667,6 +667,7 @@ void do_exit(long code)
 {
 	struct task_struct *tsk = current;
 	int group_dead;
+	TASKS_RCU(int tasks_rcu_i);
 
 	profile_task_exit(tsk);
 
@@ -775,6 +776,7 @@ void do_exit(long code)
 	 */
 	flush_ptrace_hw_breakpoint(tsk);
 
+	TASKS_RCU(tasks_rcu_i = __srcu_read_lock(&tasks_rcu_exit_srcu));
 	exit_notify(tsk, group_dead);
 	proc_exit_connector(tsk);
 #ifdef CONFIG_NUMA
@@ -814,6 +816,7 @@ void do_exit(long code)
 	if (tsk->nr_dirtied)
 		__this_cpu_add(dirty_throttle_leaks, tsk->nr_dirtied);
 	exit_rcu();
+	TASKS_RCU(__srcu_read_unlock(&tasks_rcu_exit_srcu, tasks_rcu_i));
 
 	/*
 	 * The setting of TASK_RUNNING by try_to_wake_up() may be delayed
diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
index 0955b885d0dc..540d5dfe1112 100644
--- a/kernel/locking/locktorture.c
+++ b/kernel/locking/locktorture.c
@@ -27,6 +27,7 @@
 #include <linux/kthread.h>
 #include <linux/err.h>
 #include <linux/spinlock.h>
+#include <linux/mutex.h>
 #include <linux/smp.h>
 #include <linux/interrupt.h>
 #include <linux/sched.h>
@@ -51,6 +52,8 @@ MODULE_AUTHOR("Paul E. McKenney <paulmck@us.ibm.com>");
 
 torture_param(int, nwriters_stress, -1,
 	     "Number of write-locking stress-test threads");
+torture_param(int, nreaders_stress, -1,
+	     "Number of read-locking stress-test threads");
 torture_param(int, onoff_holdoff, 0, "Time after boot before CPU hotplugs (s)");
 torture_param(int, onoff_interval, 0,
 	     "Time between CPU hotplugs (s), 0=disable");
@@ -66,30 +69,28 @@ torture_param(bool, verbose, true,
 static char *torture_type = "spin_lock";
 module_param(torture_type, charp, 0444);
 MODULE_PARM_DESC(torture_type,
-		 "Type of lock to torture (spin_lock, spin_lock_irq, ...)");
-
-static atomic_t n_lock_torture_errors;
+		 "Type of lock to torture (spin_lock, spin_lock_irq, mutex_lock, ...)");
 
 static struct task_struct *stats_task;
 static struct task_struct **writer_tasks;
+static struct task_struct **reader_tasks;
 
-static int nrealwriters_stress;
 static bool lock_is_write_held;
+static bool lock_is_read_held;
 
-struct lock_writer_stress_stats {
-	long n_write_lock_fail;
-	long n_write_lock_acquired;
+struct lock_stress_stats {
+	long n_lock_fail;
+	long n_lock_acquired;
 };
-static struct lock_writer_stress_stats *lwsa;
 
 #if defined(MODULE)
 #define LOCKTORTURE_RUNNABLE_INIT 1
 #else
 #define LOCKTORTURE_RUNNABLE_INIT 0
 #endif
-int locktorture_runnable = LOCKTORTURE_RUNNABLE_INIT;
-module_param(locktorture_runnable, int, 0444);
-MODULE_PARM_DESC(locktorture_runnable, "Start locktorture at module init");
+int torture_runnable = LOCKTORTURE_RUNNABLE_INIT;
+module_param(torture_runnable, int, 0444);
+MODULE_PARM_DESC(torture_runnable, "Start locktorture at module init");
 
 /* Forward reference. */
 static void lock_torture_cleanup(void);
@@ -102,12 +103,25 @@ struct lock_torture_ops {
 	int (*writelock)(void);
 	void (*write_delay)(struct torture_random_state *trsp);
 	void (*writeunlock)(void);
+	int (*readlock)(void);
+	void (*read_delay)(struct torture_random_state *trsp);
+	void (*readunlock)(void);
 	unsigned long flags;
 	const char *name;
 };
 
-static struct lock_torture_ops *cur_ops;
-
+struct lock_torture_cxt {
+	int nrealwriters_stress;
+	int nrealreaders_stress;
+	bool debug_lock;
+	atomic_t n_lock_torture_errors;
+	struct lock_torture_ops *cur_ops;
+	struct lock_stress_stats *lwsa; /* writer statistics */
+	struct lock_stress_stats *lrsa; /* reader statistics */
+};
+static struct lock_torture_cxt cxt = { 0, 0, false,
+				       ATOMIC_INIT(0),
+				       NULL, NULL};
 /*
  * Definitions for lock torture testing.
  */
@@ -123,10 +137,10 @@ static void torture_lock_busted_write_delay(struct torture_random_state *trsp)
 
 	/* We want a long delay occasionally to force massive contention.  */
 	if (!(torture_random(trsp) %
-	      (nrealwriters_stress * 2000 * longdelay_us)))
+	      (cxt.nrealwriters_stress * 2000 * longdelay_us)))
 		mdelay(longdelay_us);
 #ifdef CONFIG_PREEMPT
-	if (!(torture_random(trsp) % (nrealwriters_stress * 20000)))
+	if (!(torture_random(trsp) % (cxt.nrealwriters_stress * 20000)))
 		preempt_schedule();  /* Allow test to be preempted. */
 #endif
 }
@@ -140,6 +154,9 @@ static struct lock_torture_ops lock_busted_ops = {
 	.writelock	= torture_lock_busted_write_lock,
 	.write_delay	= torture_lock_busted_write_delay,
 	.writeunlock	= torture_lock_busted_write_unlock,
+	.readlock       = NULL,
+	.read_delay     = NULL,
+	.readunlock     = NULL,
 	.name		= "lock_busted"
 };
 
@@ -160,13 +177,13 @@ static void torture_spin_lock_write_delay(struct torture_random_state *trsp)
 	 * we want a long delay occasionally to force massive contention.
 	 */
 	if (!(torture_random(trsp) %
-	      (nrealwriters_stress * 2000 * longdelay_us)))
+	      (cxt.nrealwriters_stress * 2000 * longdelay_us)))
 		mdelay(longdelay_us);
 	if (!(torture_random(trsp) %
-	      (nrealwriters_stress * 2 * shortdelay_us)))
+	      (cxt.nrealwriters_stress * 2 * shortdelay_us)))
 		udelay(shortdelay_us);
 #ifdef CONFIG_PREEMPT
-	if (!(torture_random(trsp) % (nrealwriters_stress * 20000)))
+	if (!(torture_random(trsp) % (cxt.nrealwriters_stress * 20000)))
 		preempt_schedule();  /* Allow test to be preempted. */
 #endif
 }
@@ -180,6 +197,9 @@ static struct lock_torture_ops spin_lock_ops = {
 	.writelock	= torture_spin_lock_write_lock,
 	.write_delay	= torture_spin_lock_write_delay,
 	.writeunlock	= torture_spin_lock_write_unlock,
+	.readlock       = NULL,
+	.read_delay     = NULL,
+	.readunlock     = NULL,
 	.name		= "spin_lock"
 };
 
@@ -189,30 +209,137 @@ __acquires(torture_spinlock_irq)
 	unsigned long flags;
 
 	spin_lock_irqsave(&torture_spinlock, flags);
-	cur_ops->flags = flags;
+	cxt.cur_ops->flags = flags;
 	return 0;
 }
 
 static void torture_lock_spin_write_unlock_irq(void)
 __releases(torture_spinlock)
 {
-	spin_unlock_irqrestore(&torture_spinlock, cur_ops->flags);
+	spin_unlock_irqrestore(&torture_spinlock, cxt.cur_ops->flags);
 }
 
 static struct lock_torture_ops spin_lock_irq_ops = {
 	.writelock	= torture_spin_lock_write_lock_irq,
 	.write_delay	= torture_spin_lock_write_delay,
 	.writeunlock	= torture_lock_spin_write_unlock_irq,
+	.readlock       = NULL,
+	.read_delay     = NULL,
+	.readunlock     = NULL,
 	.name		= "spin_lock_irq"
 };
 
+static DEFINE_MUTEX(torture_mutex);
+
+static int torture_mutex_lock(void) __acquires(torture_mutex)
+{
+	mutex_lock(&torture_mutex);
+	return 0;
+}
+
+static void torture_mutex_delay(struct torture_random_state *trsp)
+{
+	const unsigned long longdelay_ms = 100;
+
+	/* We want a long delay occasionally to force massive contention.  */
+	if (!(torture_random(trsp) %
+	      (cxt.nrealwriters_stress * 2000 * longdelay_ms)))
+		mdelay(longdelay_ms * 5);
+	else
+		mdelay(longdelay_ms / 5);
+#ifdef CONFIG_PREEMPT
+	if (!(torture_random(trsp) % (cxt.nrealwriters_stress * 20000)))
+		preempt_schedule();  /* Allow test to be preempted. */
+#endif
+}
+
+static void torture_mutex_unlock(void) __releases(torture_mutex)
+{
+	mutex_unlock(&torture_mutex);
+}
+
+static struct lock_torture_ops mutex_lock_ops = {
+	.writelock	= torture_mutex_lock,
+	.write_delay	= torture_mutex_delay,
+	.writeunlock	= torture_mutex_unlock,
+	.readlock       = NULL,
+	.read_delay     = NULL,
+	.readunlock     = NULL,
+	.name		= "mutex_lock"
+};
+
+static DECLARE_RWSEM(torture_rwsem);
+static int torture_rwsem_down_write(void) __acquires(torture_rwsem)
+{
+	down_write(&torture_rwsem);
+	return 0;
+}
+
+static void torture_rwsem_write_delay(struct torture_random_state *trsp)
+{
+	const unsigned long longdelay_ms = 100;
+
+	/* We want a long delay occasionally to force massive contention.  */
+	if (!(torture_random(trsp) %
+	      (cxt.nrealwriters_stress * 2000 * longdelay_ms)))
+		mdelay(longdelay_ms * 10);
+	else
+		mdelay(longdelay_ms / 10);
+#ifdef CONFIG_PREEMPT
+	if (!(torture_random(trsp) % (cxt.nrealwriters_stress * 20000)))
+		preempt_schedule();  /* Allow test to be preempted. */
+#endif
+}
+
+static void torture_rwsem_up_write(void) __releases(torture_rwsem)
+{
+	up_write(&torture_rwsem);
+}
+
+static int torture_rwsem_down_read(void) __acquires(torture_rwsem)
+{
+	down_read(&torture_rwsem);
+	return 0;
+}
+
+static void torture_rwsem_read_delay(struct torture_random_state *trsp)
+{
+	const unsigned long longdelay_ms = 100;
+
+	/* We want a long delay occasionally to force massive contention.  */
+	if (!(torture_random(trsp) %
+	      (cxt.nrealwriters_stress * 2000 * longdelay_ms)))
+		mdelay(longdelay_ms * 2);
+	else
+		mdelay(longdelay_ms / 2);
+#ifdef CONFIG_PREEMPT
+	if (!(torture_random(trsp) % (cxt.nrealreaders_stress * 20000)))
+		preempt_schedule();  /* Allow test to be preempted. */
+#endif
+}
+
+static void torture_rwsem_up_read(void) __releases(torture_rwsem)
+{
+	up_read(&torture_rwsem);
+}
+
+static struct lock_torture_ops rwsem_lock_ops = {
+	.writelock	= torture_rwsem_down_write,
+	.write_delay	= torture_rwsem_write_delay,
+	.writeunlock	= torture_rwsem_up_write,
+	.readlock       = torture_rwsem_down_read,
+	.read_delay     = torture_rwsem_read_delay,
+	.readunlock     = torture_rwsem_up_read,
+	.name		= "rwsem_lock"
+};
+
 /*
  * Lock torture writer kthread.  Repeatedly acquires and releases
  * the lock, checking for duplicate acquisitions.
  */
 static int lock_torture_writer(void *arg)
 {
-	struct lock_writer_stress_stats *lwsp = arg;
+	struct lock_stress_stats *lwsp = arg;
 	static DEFINE_TORTURE_RANDOM(rand);
 
 	VERBOSE_TOROUT_STRING("lock_torture_writer task started");
@@ -221,14 +348,14 @@ static int lock_torture_writer(void *arg)
 	do {
 		if ((torture_random(&rand) & 0xfffff) == 0)
 			schedule_timeout_uninterruptible(1);
-		cur_ops->writelock();
+		cxt.cur_ops->writelock();
 		if (WARN_ON_ONCE(lock_is_write_held))
-			lwsp->n_write_lock_fail++;
+			lwsp->n_lock_fail++;
 		lock_is_write_held = 1;
-		lwsp->n_write_lock_acquired++;
-		cur_ops->write_delay(&rand);
+		lwsp->n_lock_acquired++;
+		cxt.cur_ops->write_delay(&rand);
 		lock_is_write_held = 0;
-		cur_ops->writeunlock();
+		cxt.cur_ops->writeunlock();
 		stutter_wait("lock_torture_writer");
 	} while (!torture_must_stop());
 	torture_kthread_stopping("lock_torture_writer");
@@ -236,32 +363,61 @@ static int lock_torture_writer(void *arg)
 }
 
 /*
+ * Lock torture reader kthread.  Repeatedly acquires and releases
+ * the reader lock.
+ */
+static int lock_torture_reader(void *arg)
+{
+	struct lock_stress_stats *lrsp = arg;
+	static DEFINE_TORTURE_RANDOM(rand);
+
+	VERBOSE_TOROUT_STRING("lock_torture_reader task started");
+	set_user_nice(current, MAX_NICE);
+
+	do {
+		if ((torture_random(&rand) & 0xfffff) == 0)
+			schedule_timeout_uninterruptible(1);
+		cxt.cur_ops->readlock();
+		lock_is_read_held = 1;
+		lrsp->n_lock_acquired++;
+		cxt.cur_ops->read_delay(&rand);
+		lock_is_read_held = 0;
+		cxt.cur_ops->readunlock();
+		stutter_wait("lock_torture_reader");
+	} while (!torture_must_stop());
+	torture_kthread_stopping("lock_torture_reader");
+	return 0;
+}
+
+/*
  * Create an lock-torture-statistics message in the specified buffer.
  */
-static void lock_torture_printk(char *page)
+static void __torture_print_stats(char *page,
+				  struct lock_stress_stats *statp, bool write)
 {
 	bool fail = 0;
-	int i;
+	int i, n_stress;
 	long max = 0;
-	long min = lwsa[0].n_write_lock_acquired;
+	long min = statp[0].n_lock_acquired;
 	long long sum = 0;
 
-	for (i = 0; i < nrealwriters_stress; i++) {
-		if (lwsa[i].n_write_lock_fail)
+	n_stress = write ? cxt.nrealwriters_stress : cxt.nrealreaders_stress;
+	for (i = 0; i < n_stress; i++) {
+		if (statp[i].n_lock_fail)
 			fail = true;
-		sum += lwsa[i].n_write_lock_acquired;
-		if (max < lwsa[i].n_write_lock_fail)
-			max = lwsa[i].n_write_lock_fail;
-		if (min > lwsa[i].n_write_lock_fail)
-			min = lwsa[i].n_write_lock_fail;
+		sum += statp[i].n_lock_acquired;
+		if (max < statp[i].n_lock_fail)
+			max = statp[i].n_lock_fail;
+		if (min > statp[i].n_lock_fail)
+			min = statp[i].n_lock_fail;
 	}
-	page += sprintf(page, "%s%s ", torture_type, TORTURE_FLAG);
 	page += sprintf(page,
-			"Writes:  Total: %lld  Max/Min: %ld/%ld %s  Fail: %d %s\n",
+			"%s:  Total: %lld  Max/Min: %ld/%ld %s  Fail: %d %s\n",
+			write ? "Writes" : "Reads ",
 			sum, max, min, max / 2 > min ? "???" : "",
 			fail, fail ? "!!!" : "");
 	if (fail)
-		atomic_inc(&n_lock_torture_errors);
+		atomic_inc(&cxt.n_lock_torture_errors);
 }
 
 /*
@@ -274,18 +430,35 @@ static void lock_torture_printk(char *page)
  */
 static void lock_torture_stats_print(void)
 {
-	int size = nrealwriters_stress * 200 + 8192;
+	int size = cxt.nrealwriters_stress * 200 + 8192;
 	char *buf;
 
+	if (cxt.cur_ops->readlock)
+		size += cxt.nrealreaders_stress * 200 + 8192;
+
 	buf = kmalloc(size, GFP_KERNEL);
 	if (!buf) {
 		pr_err("lock_torture_stats_print: Out of memory, need: %d",
 		       size);
 		return;
 	}
-	lock_torture_printk(buf);
+
+	__torture_print_stats(buf, cxt.lwsa, true);
 	pr_alert("%s", buf);
 	kfree(buf);
+
+	if (cxt.cur_ops->readlock) {
+		buf = kmalloc(size, GFP_KERNEL);
+		if (!buf) {
+			pr_err("lock_torture_stats_print: Out of memory, need: %d",
+			       size);
+			return;
+		}
+
+		__torture_print_stats(buf, cxt.lrsa, false);
+		pr_alert("%s", buf);
+		kfree(buf);
+	}
 }
 
 /*
@@ -312,9 +485,10 @@ lock_torture_print_module_parms(struct lock_torture_ops *cur_ops,
 				const char *tag)
 {
 	pr_alert("%s" TORTURE_FLAG
-		 "--- %s: nwriters_stress=%d stat_interval=%d verbose=%d shuffle_interval=%d stutter=%d shutdown_secs=%d onoff_interval=%d onoff_holdoff=%d\n",
-		 torture_type, tag, nrealwriters_stress, stat_interval, verbose,
-		 shuffle_interval, stutter, shutdown_secs,
+		 "--- %s%s: nwriters_stress=%d nreaders_stress=%d stat_interval=%d verbose=%d shuffle_interval=%d stutter=%d shutdown_secs=%d onoff_interval=%d onoff_holdoff=%d\n",
+		 torture_type, tag, cxt.debug_lock ? " [debug]": "",
+		 cxt.nrealwriters_stress, cxt.nrealreaders_stress, stat_interval,
+		 verbose, shuffle_interval, stutter, shutdown_secs,
 		 onoff_interval, onoff_holdoff);
 }
 
@@ -322,46 +496,56 @@ static void lock_torture_cleanup(void)
 {
 	int i;
 
-	if (torture_cleanup())
+	if (torture_cleanup_begin())
 		return;
 
 	if (writer_tasks) {
-		for (i = 0; i < nrealwriters_stress; i++)
+		for (i = 0; i < cxt.nrealwriters_stress; i++)
 			torture_stop_kthread(lock_torture_writer,
 					     writer_tasks[i]);
 		kfree(writer_tasks);
 		writer_tasks = NULL;
 	}
 
+	if (reader_tasks) {
+		for (i = 0; i < cxt.nrealreaders_stress; i++)
+			torture_stop_kthread(lock_torture_reader,
+					     reader_tasks[i]);
+		kfree(reader_tasks);
+		reader_tasks = NULL;
+	}
+
 	torture_stop_kthread(lock_torture_stats, stats_task);
 	lock_torture_stats_print();  /* -After- the stats thread is stopped! */
 
-	if (atomic_read(&n_lock_torture_errors))
-		lock_torture_print_module_parms(cur_ops,
+	if (atomic_read(&cxt.n_lock_torture_errors))
+		lock_torture_print_module_parms(cxt.cur_ops,
 						"End of test: FAILURE");
 	else if (torture_onoff_failures())
-		lock_torture_print_module_parms(cur_ops,
+		lock_torture_print_module_parms(cxt.cur_ops,
 						"End of test: LOCK_HOTPLUG");
 	else
-		lock_torture_print_module_parms(cur_ops,
+		lock_torture_print_module_parms(cxt.cur_ops,
 						"End of test: SUCCESS");
+	torture_cleanup_end();
 }
 
 static int __init lock_torture_init(void)
 {
-	int i;
+	int i, j;
 	int firsterr = 0;
 	static struct lock_torture_ops *torture_ops[] = {
 		&lock_busted_ops, &spin_lock_ops, &spin_lock_irq_ops,
+		&mutex_lock_ops, &rwsem_lock_ops,
 	};
 
-	if (!torture_init_begin(torture_type, verbose, &locktorture_runnable))
+	if (!torture_init_begin(torture_type, verbose, &torture_runnable))
 		return -EBUSY;
 
 	/* Process args and tell the world that the torturer is on the job. */
 	for (i = 0; i < ARRAY_SIZE(torture_ops); i++) {
-		cur_ops = torture_ops[i];
-		if (strcmp(torture_type, cur_ops->name) == 0)
+		cxt.cur_ops = torture_ops[i];
+		if (strcmp(torture_type, cxt.cur_ops->name) == 0)
 			break;
 	}
 	if (i == ARRAY_SIZE(torture_ops)) {
@@ -374,31 +558,68 @@ static int __init lock_torture_init(void)
 		torture_init_end();
 		return -EINVAL;
 	}
-	if (cur_ops->init)
-		cur_ops->init(); /* no "goto unwind" prior to this point!!! */
+	if (cxt.cur_ops->init)
+		cxt.cur_ops->init(); /* no "goto unwind" prior to this point!!! */
 
 	if (nwriters_stress >= 0)
-		nrealwriters_stress = nwriters_stress;
+		cxt.nrealwriters_stress = nwriters_stress;
 	else
-		nrealwriters_stress = 2 * num_online_cpus();
-	lock_torture_print_module_parms(cur_ops, "Start of test");
+		cxt.nrealwriters_stress = 2 * num_online_cpus();
+
+#ifdef CONFIG_DEBUG_MUTEXES
+	if (strncmp(torture_type, "mutex", 5) == 0)
+		cxt.debug_lock = true;
+#endif
+#ifdef CONFIG_DEBUG_SPINLOCK
+	if (strncmp(torture_type, "spin", 4) == 0)
+		cxt.debug_lock = true;
+#endif
 
 	/* Initialize the statistics so that each run gets its own numbers. */
 
 	lock_is_write_held = 0;
-	lwsa = kmalloc(sizeof(*lwsa) * nrealwriters_stress, GFP_KERNEL);
-	if (lwsa == NULL) {
-		VERBOSE_TOROUT_STRING("lwsa: Out of memory");
+	cxt.lwsa = kmalloc(sizeof(*cxt.lwsa) * cxt.nrealwriters_stress, GFP_KERNEL);
+	if (cxt.lwsa == NULL) {
+		VERBOSE_TOROUT_STRING("cxt.lwsa: Out of memory");
 		firsterr = -ENOMEM;
 		goto unwind;
 	}
-	for (i = 0; i < nrealwriters_stress; i++) {
-		lwsa[i].n_write_lock_fail = 0;
-		lwsa[i].n_write_lock_acquired = 0;
+	for (i = 0; i < cxt.nrealwriters_stress; i++) {
+		cxt.lwsa[i].n_lock_fail = 0;
+		cxt.lwsa[i].n_lock_acquired = 0;
 	}
 
-	/* Start up the kthreads. */
+	if (cxt.cur_ops->readlock) {
+		if (nreaders_stress >= 0)
+			cxt.nrealreaders_stress = nreaders_stress;
+		else {
+			/*
+			 * By default distribute evenly the number of
+			 * readers and writers. We still run the same number
+			 * of threads as the writer-only locks default.
+			 */
+			if (nwriters_stress < 0) /* user doesn't care */
+				cxt.nrealwriters_stress = num_online_cpus();
+			cxt.nrealreaders_stress = cxt.nrealwriters_stress;
+		}
+
+		lock_is_read_held = 0;
+		cxt.lrsa = kmalloc(sizeof(*cxt.lrsa) * cxt.nrealreaders_stress, GFP_KERNEL);
+		if (cxt.lrsa == NULL) {
+			VERBOSE_TOROUT_STRING("cxt.lrsa: Out of memory");
+			firsterr = -ENOMEM;
+			kfree(cxt.lwsa);
+			goto unwind;
+		}
+
+		for (i = 0; i < cxt.nrealreaders_stress; i++) {
+			cxt.lrsa[i].n_lock_fail = 0;
+			cxt.lrsa[i].n_lock_acquired = 0;
+		}
+	}
+	lock_torture_print_module_parms(cxt.cur_ops, "Start of test");
 
+	/* Prepare torture context. */
 	if (onoff_interval > 0) {
 		firsterr = torture_onoff_init(onoff_holdoff * HZ,
 					      onoff_interval * HZ);
@@ -422,18 +643,51 @@ static int __init lock_torture_init(void)
 			goto unwind;
 	}
 
-	writer_tasks = kzalloc(nrealwriters_stress * sizeof(writer_tasks[0]),
+	writer_tasks = kzalloc(cxt.nrealwriters_stress * sizeof(writer_tasks[0]),
 			       GFP_KERNEL);
 	if (writer_tasks == NULL) {
 		VERBOSE_TOROUT_ERRSTRING("writer_tasks: Out of memory");
 		firsterr = -ENOMEM;
 		goto unwind;
 	}
-	for (i = 0; i < nrealwriters_stress; i++) {
-		firsterr = torture_create_kthread(lock_torture_writer, &lwsa[i],
+
+	if (cxt.cur_ops->readlock) {
+		reader_tasks = kzalloc(cxt.nrealreaders_stress * sizeof(reader_tasks[0]),
+				       GFP_KERNEL);
+		if (reader_tasks == NULL) {
+			VERBOSE_TOROUT_ERRSTRING("reader_tasks: Out of memory");
+			firsterr = -ENOMEM;
+			goto unwind;
+		}
+	}
+
+	/*
+	 * Create the kthreads and start torturing (oh, those poor little locks).
+	 *
+	 * TODO: Note that we interleave writers with readers, giving writers a
+	 * slight advantage, by creating its kthread first. This can be modified
+	 * for very specific needs, or even let the user choose the policy, if
+	 * ever wanted.
+	 */
+	for (i = 0, j = 0; i < cxt.nrealwriters_stress ||
+		    j < cxt.nrealreaders_stress; i++, j++) {
+		if (i >= cxt.nrealwriters_stress)
+			goto create_reader;
+
+		/* Create writer. */
+		firsterr = torture_create_kthread(lock_torture_writer, &cxt.lwsa[i],
 						  writer_tasks[i]);
 		if (firsterr)
 			goto unwind;
+
+	create_reader:
+		if (cxt.cur_ops->readlock == NULL || (j >= cxt.nrealreaders_stress))
+			continue;
+		/* Create reader. */
+		firsterr = torture_create_kthread(lock_torture_reader, &cxt.lrsa[j],
+						  reader_tasks[j]);
+		if (firsterr)
+			goto unwind;
 	}
 	if (stat_interval > 0) {
 		firsterr = torture_create_kthread(lock_torture_stats, NULL,
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 948a7693748e..240fa9094f83 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -49,11 +49,19 @@
 #include <linux/trace_clock.h>
 #include <asm/byteorder.h>
 #include <linux/torture.h>
+#include <linux/vmalloc.h>
 
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Paul E. McKenney <paulmck@us.ibm.com> and Josh Triplett <josh@joshtriplett.org>");
 
 
+torture_param(int, cbflood_inter_holdoff, HZ,
+	      "Holdoff between floods (jiffies)");
+torture_param(int, cbflood_intra_holdoff, 1,
+	      "Holdoff between bursts (jiffies)");
+torture_param(int, cbflood_n_burst, 3, "# bursts in flood, zero to disable");
+torture_param(int, cbflood_n_per_burst, 20000,
+	      "# callbacks per burst in flood");
 torture_param(int, fqs_duration, 0,
 	      "Duration of fqs bursts (us), 0 to disable");
 torture_param(int, fqs_holdoff, 0, "Holdoff time within fqs bursts (us)");
@@ -96,10 +104,12 @@ module_param(torture_type, charp, 0444);
 MODULE_PARM_DESC(torture_type, "Type of RCU to torture (rcu, rcu_bh, ...)");
 
 static int nrealreaders;
+static int ncbflooders;
 static struct task_struct *writer_task;
 static struct task_struct **fakewriter_tasks;
 static struct task_struct **reader_tasks;
 static struct task_struct *stats_task;
+static struct task_struct **cbflood_task;
 static struct task_struct *fqs_task;
 static struct task_struct *boost_tasks[NR_CPUS];
 static struct task_struct *stall_task;
@@ -138,6 +148,7 @@ static long n_rcu_torture_boosts;
 static long n_rcu_torture_timers;
 static long n_barrier_attempts;
 static long n_barrier_successes;
+static atomic_long_t n_cbfloods;
 static struct list_head rcu_torture_removed;
 
 static int rcu_torture_writer_state;
@@ -157,9 +168,9 @@ static int rcu_torture_writer_state;
 #else
 #define RCUTORTURE_RUNNABLE_INIT 0
 #endif
-int rcutorture_runnable = RCUTORTURE_RUNNABLE_INIT;
-module_param(rcutorture_runnable, int, 0444);
-MODULE_PARM_DESC(rcutorture_runnable, "Start rcutorture at boot");
+static int torture_runnable = RCUTORTURE_RUNNABLE_INIT;
+module_param(torture_runnable, int, 0444);
+MODULE_PARM_DESC(torture_runnable, "Start rcutorture at boot");
 
 #if defined(CONFIG_RCU_BOOST) && !defined(CONFIG_HOTPLUG_CPU)
 #define rcu_can_boost() 1
@@ -182,7 +193,7 @@ static u64 notrace rcu_trace_clock_local(void)
 #endif /* #else #ifdef CONFIG_RCU_TRACE */
 
 static unsigned long boost_starttime;	/* jiffies of next boost test start. */
-DEFINE_MUTEX(boost_mutex);		/* protect setting boost_starttime */
+static DEFINE_MUTEX(boost_mutex);	/* protect setting boost_starttime */
 					/*  and boost task create/destroy. */
 static atomic_t barrier_cbs_count;	/* Barrier callbacks registered. */
 static bool barrier_phase;		/* Test phase. */
@@ -242,7 +253,7 @@ struct rcu_torture_ops {
 	void (*call)(struct rcu_head *head, void (*func)(struct rcu_head *rcu));
 	void (*cb_barrier)(void);
 	void (*fqs)(void);
-	void (*stats)(char *page);
+	void (*stats)(void);
 	int irq_capable;
 	int can_boost;
 	const char *name;
@@ -525,21 +536,21 @@ static void srcu_torture_barrier(void)
 	srcu_barrier(&srcu_ctl);
 }
 
-static void srcu_torture_stats(char *page)
+static void srcu_torture_stats(void)
 {
 	int cpu;
 	int idx = srcu_ctl.completed & 0x1;
 
-	page += sprintf(page, "%s%s per-CPU(idx=%d):",
-		       torture_type, TORTURE_FLAG, idx);
+	pr_alert("%s%s per-CPU(idx=%d):",
+		 torture_type, TORTURE_FLAG, idx);
 	for_each_possible_cpu(cpu) {
 		long c0, c1;
 
 		c0 = (long)per_cpu_ptr(srcu_ctl.per_cpu_ref, cpu)->c[!idx];
 		c1 = (long)per_cpu_ptr(srcu_ctl.per_cpu_ref, cpu)->c[idx];
-		page += sprintf(page, " %d(%ld,%ld)", cpu, c0, c1);
+		pr_cont(" %d(%ld,%ld)", cpu, c0, c1);
 	}
-	sprintf(page, "\n");
+	pr_cont("\n");
 }
 
 static void srcu_torture_synchronize_expedited(void)
@@ -601,6 +612,52 @@ static struct rcu_torture_ops sched_ops = {
 	.name		= "sched"
 };
 
+#ifdef CONFIG_TASKS_RCU
+
+/*
+ * Definitions for RCU-tasks torture testing.
+ */
+
+static int tasks_torture_read_lock(void)
+{
+	return 0;
+}
+
+static void tasks_torture_read_unlock(int idx)
+{
+}
+
+static void rcu_tasks_torture_deferred_free(struct rcu_torture *p)
+{
+	call_rcu_tasks(&p->rtort_rcu, rcu_torture_cb);
+}
+
+static struct rcu_torture_ops tasks_ops = {
+	.ttype		= RCU_TASKS_FLAVOR,
+	.init		= rcu_sync_torture_init,
+	.readlock	= tasks_torture_read_lock,
+	.read_delay	= rcu_read_delay,  /* just reuse rcu's version. */
+	.readunlock	= tasks_torture_read_unlock,
+	.completed	= rcu_no_completed,
+	.deferred_free	= rcu_tasks_torture_deferred_free,
+	.sync		= synchronize_rcu_tasks,
+	.exp_sync	= synchronize_rcu_tasks,
+	.call		= call_rcu_tasks,
+	.cb_barrier	= rcu_barrier_tasks,
+	.fqs		= NULL,
+	.stats		= NULL,
+	.irq_capable	= 1,
+	.name		= "tasks"
+};
+
+#define RCUTORTURE_TASKS_OPS &tasks_ops,
+
+#else /* #ifdef CONFIG_TASKS_RCU */
+
+#define RCUTORTURE_TASKS_OPS
+
+#endif /* #else #ifdef CONFIG_TASKS_RCU */
+
 /*
  * RCU torture priority-boost testing.  Runs one real-time thread per
  * CPU for moderate bursts, repeatedly registering RCU callbacks and
@@ -667,7 +724,7 @@ static int rcu_torture_boost(void *arg)
 				}
 				call_rcu_time = jiffies;
 			}
-			cond_resched();
+			cond_resched_rcu_qs();
 			stutter_wait("rcu_torture_boost");
 			if (torture_must_stop())
 				goto checkwait;
@@ -707,6 +764,58 @@ checkwait:	stutter_wait("rcu_torture_boost");
 	return 0;
 }
 
+static void rcu_torture_cbflood_cb(struct rcu_head *rhp)
+{
+}
+
+/*
+ * RCU torture callback-flood kthread.  Repeatedly induces bursts of calls
+ * to call_rcu() or analogous, increasing the probability of occurrence
+ * of callback-overflow corner cases.
+ */
+static int
+rcu_torture_cbflood(void *arg)
+{
+	int err = 1;
+	int i;
+	int j;
+	struct rcu_head *rhp;
+
+	if (cbflood_n_per_burst > 0 &&
+	    cbflood_inter_holdoff > 0 &&
+	    cbflood_intra_holdoff > 0 &&
+	    cur_ops->call &&
+	    cur_ops->cb_barrier) {
+		rhp = vmalloc(sizeof(*rhp) *
+			      cbflood_n_burst * cbflood_n_per_burst);
+		err = !rhp;
+	}
+	if (err) {
+		VERBOSE_TOROUT_STRING("rcu_torture_cbflood disabled: Bad args or OOM");
+		while (!torture_must_stop())
+			schedule_timeout_interruptible(HZ);
+		return 0;
+	}
+	VERBOSE_TOROUT_STRING("rcu_torture_cbflood task started");
+	do {
+		schedule_timeout_interruptible(cbflood_inter_holdoff);
+		atomic_long_inc(&n_cbfloods);
+		WARN_ON(signal_pending(current));
+		for (i = 0; i < cbflood_n_burst; i++) {
+			for (j = 0; j < cbflood_n_per_burst; j++) {
+				cur_ops->call(&rhp[i * cbflood_n_per_burst + j],
+					      rcu_torture_cbflood_cb);
+			}
+			schedule_timeout_interruptible(cbflood_intra_holdoff);
+			WARN_ON(signal_pending(current));
+		}
+		cur_ops->cb_barrier();
+		stutter_wait("rcu_torture_cbflood");
+	} while (!torture_must_stop());
+	torture_kthread_stopping("rcu_torture_cbflood");
+	return 0;
+}
+
 /*
  * RCU torture force-quiescent-state kthread.  Repeatedly induces
  * bursts of calls to force_quiescent_state(), increasing the probability
@@ -1019,7 +1128,7 @@ rcu_torture_reader(void *arg)
 		__this_cpu_inc(rcu_torture_batch[completed]);
 		preempt_enable();
 		cur_ops->readunlock(idx);
-		cond_resched();
+		cond_resched_rcu_qs();
 		stutter_wait("rcu_torture_reader");
 	} while (!torture_must_stop());
 	if (irqreader && cur_ops->irq_capable) {
@@ -1031,10 +1140,15 @@ rcu_torture_reader(void *arg)
 }
 
 /*
- * Create an RCU-torture statistics message in the specified buffer.
+ * Print torture statistics.  Caller must ensure that there is only
+ * one call to this function at a given time!!!  This is normally
+ * accomplished by relying on the module system to only have one copy
+ * of the module loaded, and then by giving the rcu_torture_stats
+ * kthread full control (or the init/cleanup functions when rcu_torture_stats
+ * thread is not running).
  */
 static void
-rcu_torture_printk(char *page)
+rcu_torture_stats_print(void)
 {
 	int cpu;
 	int i;
@@ -1052,55 +1166,61 @@ rcu_torture_printk(char *page)
 		if (pipesummary[i] != 0)
 			break;
 	}
-	page += sprintf(page, "%s%s ", torture_type, TORTURE_FLAG);
-	page += sprintf(page,
-		       "rtc: %p ver: %lu tfle: %d rta: %d rtaf: %d rtf: %d ",
-		       rcu_torture_current,
-		       rcu_torture_current_version,
-		       list_empty(&rcu_torture_freelist),
-		       atomic_read(&n_rcu_torture_alloc),
-		       atomic_read(&n_rcu_torture_alloc_fail),
-		       atomic_read(&n_rcu_torture_free));
-	page += sprintf(page, "rtmbe: %d rtbke: %ld rtbre: %ld ",
-		       atomic_read(&n_rcu_torture_mberror),
-		       n_rcu_torture_boost_ktrerror,
-		       n_rcu_torture_boost_rterror);
-	page += sprintf(page, "rtbf: %ld rtb: %ld nt: %ld ",
-		       n_rcu_torture_boost_failure,
-		       n_rcu_torture_boosts,
-		       n_rcu_torture_timers);
-	page = torture_onoff_stats(page);
-	page += sprintf(page, "barrier: %ld/%ld:%ld",
-		       n_barrier_successes,
-		       n_barrier_attempts,
-		       n_rcu_torture_barrier_error);
-	page += sprintf(page, "\n%s%s ", torture_type, TORTURE_FLAG);
+
+	pr_alert("%s%s ", torture_type, TORTURE_FLAG);
+	pr_cont("rtc: %p ver: %lu tfle: %d rta: %d rtaf: %d rtf: %d ",
+		rcu_torture_current,
+		rcu_torture_current_version,
+		list_empty(&rcu_torture_freelist),
+		atomic_read(&n_rcu_torture_alloc),
+		atomic_read(&n_rcu_torture_alloc_fail),
+		atomic_read(&n_rcu_torture_free));
+	pr_cont("rtmbe: %d rtbke: %ld rtbre: %ld ",
+		atomic_read(&n_rcu_torture_mberror),
+		n_rcu_torture_boost_ktrerror,
+		n_rcu_torture_boost_rterror);
+	pr_cont("rtbf: %ld rtb: %ld nt: %ld ",
+		n_rcu_torture_boost_failure,
+		n_rcu_torture_boosts,
+		n_rcu_torture_timers);
+	torture_onoff_stats();
+	pr_cont("barrier: %ld/%ld:%ld ",
+		n_barrier_successes,
+		n_barrier_attempts,
+		n_rcu_torture_barrier_error);
+	pr_cont("cbflood: %ld\n", atomic_long_read(&n_cbfloods));
+
+	pr_alert("%s%s ", torture_type, TORTURE_FLAG);
 	if (atomic_read(&n_rcu_torture_mberror) != 0 ||
 	    n_rcu_torture_barrier_error != 0 ||
 	    n_rcu_torture_boost_ktrerror != 0 ||
 	    n_rcu_torture_boost_rterror != 0 ||
 	    n_rcu_torture_boost_failure != 0 ||
 	    i > 1) {
-		page += sprintf(page, "!!! ");
+		pr_cont("%s", "!!! ");
 		atomic_inc(&n_rcu_torture_error);
 		WARN_ON_ONCE(1);
 	}
-	page += sprintf(page, "Reader Pipe: ");
+	pr_cont("Reader Pipe: ");
 	for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++)
-		page += sprintf(page, " %ld", pipesummary[i]);
-	page += sprintf(page, "\n%s%s ", torture_type, TORTURE_FLAG);
-	page += sprintf(page, "Reader Batch: ");
+		pr_cont(" %ld", pipesummary[i]);
+	pr_cont("\n");
+
+	pr_alert("%s%s ", torture_type, TORTURE_FLAG);
+	pr_cont("Reader Batch: ");
 	for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++)
-		page += sprintf(page, " %ld", batchsummary[i]);
-	page += sprintf(page, "\n%s%s ", torture_type, TORTURE_FLAG);
-	page += sprintf(page, "Free-Block Circulation: ");
+		pr_cont(" %ld", batchsummary[i]);
+	pr_cont("\n");
+
+	pr_alert("%s%s ", torture_type, TORTURE_FLAG);
+	pr_cont("Free-Block Circulation: ");
 	for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++) {
-		page += sprintf(page, " %d",
-			       atomic_read(&rcu_torture_wcount[i]));
+		pr_cont(" %d", atomic_read(&rcu_torture_wcount[i]));
 	}
-	page += sprintf(page, "\n");
+	pr_cont("\n");
+
 	if (cur_ops->stats)
-		cur_ops->stats(page);
+		cur_ops->stats();
 	if (rtcv_snap == rcu_torture_current_version &&
 	    rcu_torture_current != NULL) {
 		int __maybe_unused flags;
@@ -1109,10 +1229,9 @@ rcu_torture_printk(char *page)
 
 		rcutorture_get_gp_data(cur_ops->ttype,
 				       &flags, &gpnum, &completed);
-		page += sprintf(page,
-				"??? Writer stall state %d g%lu c%lu f%#x\n",
-				rcu_torture_writer_state,
-				gpnum, completed, flags);
+		pr_alert("??? Writer stall state %d g%lu c%lu f%#x\n",
+			 rcu_torture_writer_state,
+			 gpnum, completed, flags);
 		show_rcu_gp_kthreads();
 		rcutorture_trace_dump();
 	}
@@ -1120,30 +1239,6 @@ rcu_torture_printk(char *page)
 }
 
 /*
- * Print torture statistics.  Caller must ensure that there is only
- * one call to this function at a given time!!!  This is normally
- * accomplished by relying on the module system to only have one copy
- * of the module loaded, and then by giving the rcu_torture_stats
- * kthread full control (or the init/cleanup functions when rcu_torture_stats
- * thread is not running).
- */
-static void
-rcu_torture_stats_print(void)
-{
-	int size = nr_cpu_ids * 200 + 8192;
-	char *buf;
-
-	buf = kmalloc(size, GFP_KERNEL);
-	if (!buf) {
-		pr_err("rcu-torture: Out of memory, need: %d", size);
-		return;
-	}
-	rcu_torture_printk(buf);
-	pr_alert("%s", buf);
-	kfree(buf);
-}
-
-/*
  * Periodically prints torture statistics, if periodic statistics printing
  * was specified via the stat_interval module parameter.
  */
@@ -1295,7 +1390,8 @@ static int rcu_torture_barrier_cbs(void *arg)
 		if (atomic_dec_and_test(&barrier_cbs_count))
 			wake_up(&barrier_wq);
 	} while (!torture_must_stop());
-	cur_ops->cb_barrier();
+	if (cur_ops->cb_barrier != NULL)
+		cur_ops->cb_barrier();
 	destroy_rcu_head_on_stack(&rcu);
 	torture_kthread_stopping("rcu_torture_barrier_cbs");
 	return 0;
@@ -1418,7 +1514,7 @@ rcu_torture_cleanup(void)
 	int i;
 
 	rcutorture_record_test_transition();
-	if (torture_cleanup()) {
+	if (torture_cleanup_begin()) {
 		if (cur_ops->cb_barrier != NULL)
 			cur_ops->cb_barrier();
 		return;
@@ -1447,6 +1543,8 @@ rcu_torture_cleanup(void)
 
 	torture_stop_kthread(rcu_torture_stats, stats_task);
 	torture_stop_kthread(rcu_torture_fqs, fqs_task);
+	for (i = 0; i < ncbflooders; i++)
+		torture_stop_kthread(rcu_torture_cbflood, cbflood_task[i]);
 	if ((test_boost == 1 && cur_ops->can_boost) ||
 	    test_boost == 2) {
 		unregister_cpu_notifier(&rcutorture_cpu_nb);
@@ -1468,6 +1566,7 @@ rcu_torture_cleanup(void)
 					       "End of test: RCU_HOTPLUG");
 	else
 		rcu_torture_print_module_parms(cur_ops, "End of test: SUCCESS");
+	torture_cleanup_end();
 }
 
 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
@@ -1534,9 +1633,10 @@ rcu_torture_init(void)
 	int firsterr = 0;
 	static struct rcu_torture_ops *torture_ops[] = {
 		&rcu_ops, &rcu_bh_ops, &rcu_busted_ops, &srcu_ops, &sched_ops,
+		RCUTORTURE_TASKS_OPS
 	};
 
-	if (!torture_init_begin(torture_type, verbose, &rcutorture_runnable))
+	if (!torture_init_begin(torture_type, verbose, &torture_runnable))
 		return -EBUSY;
 
 	/* Process args and tell the world that the torturer is on the job. */
@@ -1693,6 +1793,24 @@ rcu_torture_init(void)
 		goto unwind;
 	if (object_debug)
 		rcu_test_debug_objects();
+	if (cbflood_n_burst > 0) {
+		/* Create the cbflood threads */
+		ncbflooders = (num_online_cpus() + 3) / 4;
+		cbflood_task = kcalloc(ncbflooders, sizeof(*cbflood_task),
+				       GFP_KERNEL);
+		if (!cbflood_task) {
+			VERBOSE_TOROUT_ERRSTRING("out of memory");
+			firsterr = -ENOMEM;
+			goto unwind;
+		}
+		for (i = 0; i < ncbflooders; i++) {
+			firsterr = torture_create_kthread(rcu_torture_cbflood,
+							  NULL,
+							  cbflood_task[i]);
+			if (firsterr)
+				goto unwind;
+		}
+	}
 	rcutorture_record_test_transition();
 	torture_init_end();
 	return 0;
diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
index d9efcc13008c..c0623fc47125 100644
--- a/kernel/rcu/tiny.c
+++ b/kernel/rcu/tiny.c
@@ -51,7 +51,7 @@ static long long rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
 
 #include "tiny_plugin.h"
 
-/* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcutree.c. */
+/* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcu/tree.c. */
 static void rcu_idle_enter_common(long long newval)
 {
 	if (newval) {
@@ -62,7 +62,7 @@ static void rcu_idle_enter_common(long long newval)
 	}
 	RCU_TRACE(trace_rcu_dyntick(TPS("Start"),
 				    rcu_dynticks_nesting, newval));
-	if (!is_idle_task(current)) {
+	if (IS_ENABLED(CONFIG_RCU_TRACE) && !is_idle_task(current)) {
 		struct task_struct *idle __maybe_unused = idle_task(smp_processor_id());
 
 		RCU_TRACE(trace_rcu_dyntick(TPS("Entry error: not idle task"),
@@ -72,7 +72,7 @@ static void rcu_idle_enter_common(long long newval)
 			  current->pid, current->comm,
 			  idle->pid, idle->comm); /* must be idle task! */
 	}
-	rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
+	rcu_sched_qs(); /* implies rcu_bh_inc() */
 	barrier();
 	rcu_dynticks_nesting = newval;
 }
@@ -114,7 +114,7 @@ void rcu_irq_exit(void)
 }
 EXPORT_SYMBOL_GPL(rcu_irq_exit);
 
-/* Common code for rcu_idle_exit() and rcu_irq_enter(), see kernel/rcutree.c. */
+/* Common code for rcu_idle_exit() and rcu_irq_enter(), see kernel/rcu/tree.c. */
 static void rcu_idle_exit_common(long long oldval)
 {
 	if (oldval) {
@@ -123,7 +123,7 @@ static void rcu_idle_exit_common(long long oldval)
 		return;
 	}
 	RCU_TRACE(trace_rcu_dyntick(TPS("End"), oldval, rcu_dynticks_nesting));
-	if (!is_idle_task(current)) {
+	if (IS_ENABLED(CONFIG_RCU_TRACE) && !is_idle_task(current)) {
 		struct task_struct *idle __maybe_unused = idle_task(smp_processor_id());
 
 		RCU_TRACE(trace_rcu_dyntick(TPS("Exit error: not idle task"),
@@ -217,7 +217,7 @@ static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
  * 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)
+void rcu_sched_qs(void)
 {
 	unsigned long flags;
 
@@ -231,7 +231,7 @@ void rcu_sched_qs(int cpu)
 /*
  * Record an rcu_bh quiescent state.
  */
-void rcu_bh_qs(int cpu)
+void rcu_bh_qs(void)
 {
 	unsigned long flags;
 
@@ -251,9 +251,11 @@ void rcu_check_callbacks(int cpu, int user)
 {
 	RCU_TRACE(check_cpu_stalls());
 	if (user || rcu_is_cpu_rrupt_from_idle())
-		rcu_sched_qs(cpu);
+		rcu_sched_qs();
 	else if (!in_softirq())
-		rcu_bh_qs(cpu);
+		rcu_bh_qs();
+	if (user)
+		rcu_note_voluntary_context_switch(current);
 }
 
 /*
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 1b70cb6fbe3c..133e47223095 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -79,9 +79,18 @@ static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
  * the tracing userspace tools to be able to decipher the string
  * address to the matching string.
  */
-#define RCU_STATE_INITIALIZER(sname, sabbr, cr) \
+#ifdef CONFIG_TRACING
+# define DEFINE_RCU_TPS(sname) \
 static char sname##_varname[] = #sname; \
-static const char *tp_##sname##_varname __used __tracepoint_string = sname##_varname; \
+static const char *tp_##sname##_varname __used __tracepoint_string = sname##_varname;
+# define RCU_STATE_NAME(sname) sname##_varname
+#else
+# define DEFINE_RCU_TPS(sname)
+# define RCU_STATE_NAME(sname) __stringify(sname)
+#endif
+
+#define RCU_STATE_INITIALIZER(sname, sabbr, cr) \
+DEFINE_RCU_TPS(sname) \
 struct rcu_state sname##_state = { \
 	.level = { &sname##_state.node[0] }, \
 	.call = cr, \
@@ -93,7 +102,7 @@ struct rcu_state sname##_state = { \
 	.orphan_donetail = &sname##_state.orphan_donelist, \
 	.barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \
 	.onoff_mutex = __MUTEX_INITIALIZER(sname##_state.onoff_mutex), \
-	.name = sname##_varname, \
+	.name = RCU_STATE_NAME(sname), \
 	.abbr = sabbr, \
 }; \
 DEFINE_PER_CPU(struct rcu_data, sname##_data)
@@ -188,22 +197,24 @@ static int rcu_gp_in_progress(struct rcu_state *rsp)
  * one since the start of the grace period, this just sets a flag.
  * The caller must have disabled preemption.
  */
-void rcu_sched_qs(int cpu)
+void rcu_sched_qs(void)
 {
-	struct rcu_data *rdp = &per_cpu(rcu_sched_data, cpu);
-
-	if (rdp->passed_quiesce == 0)
-		trace_rcu_grace_period(TPS("rcu_sched"), rdp->gpnum, TPS("cpuqs"));
-	rdp->passed_quiesce = 1;
+	if (!__this_cpu_read(rcu_sched_data.passed_quiesce)) {
+		trace_rcu_grace_period(TPS("rcu_sched"),
+				       __this_cpu_read(rcu_sched_data.gpnum),
+				       TPS("cpuqs"));
+		__this_cpu_write(rcu_sched_data.passed_quiesce, 1);
+	}
 }
 
-void rcu_bh_qs(int cpu)
+void rcu_bh_qs(void)
 {
-	struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu);
-
-	if (rdp->passed_quiesce == 0)
-		trace_rcu_grace_period(TPS("rcu_bh"), rdp->gpnum, TPS("cpuqs"));
-	rdp->passed_quiesce = 1;
+	if (!__this_cpu_read(rcu_bh_data.passed_quiesce)) {
+		trace_rcu_grace_period(TPS("rcu_bh"),
+				       __this_cpu_read(rcu_bh_data.gpnum),
+				       TPS("cpuqs"));
+		__this_cpu_write(rcu_bh_data.passed_quiesce, 1);
+	}
 }
 
 static DEFINE_PER_CPU(int, rcu_sched_qs_mask);
@@ -278,7 +289,7 @@ static void rcu_momentary_dyntick_idle(void)
 void rcu_note_context_switch(int cpu)
 {
 	trace_rcu_utilization(TPS("Start context switch"));
-	rcu_sched_qs(cpu);
+	rcu_sched_qs();
 	rcu_preempt_note_context_switch(cpu);
 	if (unlikely(raw_cpu_read(rcu_sched_qs_mask)))
 		rcu_momentary_dyntick_idle();
@@ -526,6 +537,7 @@ static void rcu_eqs_enter_common(struct rcu_dynticks *rdtp, long long oldval,
 	atomic_inc(&rdtp->dynticks);
 	smp_mb__after_atomic();  /* Force ordering with next sojourn. */
 	WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
+	rcu_dynticks_task_enter();
 
 	/*
 	 * It is illegal to enter an extended quiescent state while
@@ -642,6 +654,7 @@ void rcu_irq_exit(void)
 static void rcu_eqs_exit_common(struct rcu_dynticks *rdtp, long long oldval,
 			       int user)
 {
+	rcu_dynticks_task_exit();
 	smp_mb__before_atomic();  /* Force ordering w/previous sojourn. */
 	atomic_inc(&rdtp->dynticks);
 	/* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
@@ -819,7 +832,7 @@ bool notrace __rcu_is_watching(void)
  */
 bool notrace rcu_is_watching(void)
 {
-	int ret;
+	bool ret;
 
 	preempt_disable();
 	ret = __rcu_is_watching();
@@ -1647,7 +1660,7 @@ static int rcu_gp_init(struct rcu_state *rsp)
 					    rnp->level, rnp->grplo,
 					    rnp->grphi, rnp->qsmask);
 		raw_spin_unlock_irq(&rnp->lock);
-		cond_resched();
+		cond_resched_rcu_qs();
 	}
 
 	mutex_unlock(&rsp->onoff_mutex);
@@ -1668,7 +1681,7 @@ static int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in)
 	if (fqs_state == RCU_SAVE_DYNTICK) {
 		/* Collect dyntick-idle snapshots. */
 		if (is_sysidle_rcu_state(rsp)) {
-			isidle = 1;
+			isidle = true;
 			maxj = jiffies - ULONG_MAX / 4;
 		}
 		force_qs_rnp(rsp, dyntick_save_progress_counter,
@@ -1677,14 +1690,15 @@ static int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in)
 		fqs_state = RCU_FORCE_QS;
 	} else {
 		/* Handle dyntick-idle and offline CPUs. */
-		isidle = 0;
+		isidle = false;
 		force_qs_rnp(rsp, rcu_implicit_dynticks_qs, &isidle, &maxj);
 	}
 	/* Clear flag to prevent immediate re-entry. */
 	if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
 		raw_spin_lock_irq(&rnp->lock);
 		smp_mb__after_unlock_lock();
-		ACCESS_ONCE(rsp->gp_flags) &= ~RCU_GP_FLAG_FQS;
+		ACCESS_ONCE(rsp->gp_flags) =
+			ACCESS_ONCE(rsp->gp_flags) & ~RCU_GP_FLAG_FQS;
 		raw_spin_unlock_irq(&rnp->lock);
 	}
 	return fqs_state;
@@ -1736,7 +1750,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
 		/* smp_mb() provided by prior unlock-lock pair. */
 		nocb += rcu_future_gp_cleanup(rsp, rnp);
 		raw_spin_unlock_irq(&rnp->lock);
-		cond_resched();
+		cond_resched_rcu_qs();
 	}
 	rnp = rcu_get_root(rsp);
 	raw_spin_lock_irq(&rnp->lock);
@@ -1785,8 +1799,8 @@ static int __noreturn rcu_gp_kthread(void *arg)
 			/* Locking provides needed memory barrier. */
 			if (rcu_gp_init(rsp))
 				break;
-			cond_resched();
-			flush_signals(current);
+			cond_resched_rcu_qs();
+			WARN_ON(signal_pending(current));
 			trace_rcu_grace_period(rsp->name,
 					       ACCESS_ONCE(rsp->gpnum),
 					       TPS("reqwaitsig"));
@@ -1828,11 +1842,11 @@ static int __noreturn rcu_gp_kthread(void *arg)
 				trace_rcu_grace_period(rsp->name,
 						       ACCESS_ONCE(rsp->gpnum),
 						       TPS("fqsend"));
-				cond_resched();
+				cond_resched_rcu_qs();
 			} else {
 				/* Deal with stray signal. */
-				cond_resched();
-				flush_signals(current);
+				cond_resched_rcu_qs();
+				WARN_ON(signal_pending(current));
 				trace_rcu_grace_period(rsp->name,
 						       ACCESS_ONCE(rsp->gpnum),
 						       TPS("fqswaitsig"));
@@ -1928,7 +1942,7 @@ static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
 {
 	WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
 	raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags);
-	wake_up(&rsp->gp_wq);  /* Memory barrier implied by wake_up() path. */
+	rcu_gp_kthread_wake(rsp);
 }
 
 /*
@@ -2210,8 +2224,6 @@ static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
 	/* Adjust any no-longer-needed kthreads. */
 	rcu_boost_kthread_setaffinity(rnp, -1);
 
-	/* Remove the dead CPU from the bitmasks in the rcu_node hierarchy. */
-
 	/* Exclude any attempts to start a new grace period. */
 	mutex_lock(&rsp->onoff_mutex);
 	raw_spin_lock_irqsave(&rsp->orphan_lock, flags);
@@ -2393,8 +2405,8 @@ void rcu_check_callbacks(int cpu, int user)
 		 * at least not while the corresponding CPU is online.
 		 */
 
-		rcu_sched_qs(cpu);
-		rcu_bh_qs(cpu);
+		rcu_sched_qs();
+		rcu_bh_qs();
 
 	} else if (!in_softirq()) {
 
@@ -2405,11 +2417,13 @@ void rcu_check_callbacks(int cpu, int user)
 		 * critical section, so note it.
 		 */
 
-		rcu_bh_qs(cpu);
+		rcu_bh_qs();
 	}
 	rcu_preempt_check_callbacks(cpu);
 	if (rcu_pending(cpu))
 		invoke_rcu_core();
+	if (user)
+		rcu_note_voluntary_context_switch(current);
 	trace_rcu_utilization(TPS("End scheduler-tick"));
 }
 
@@ -2432,7 +2446,7 @@ static void force_qs_rnp(struct rcu_state *rsp,
 	struct rcu_node *rnp;
 
 	rcu_for_each_leaf_node(rsp, rnp) {
-		cond_resched();
+		cond_resched_rcu_qs();
 		mask = 0;
 		raw_spin_lock_irqsave(&rnp->lock, flags);
 		smp_mb__after_unlock_lock();
@@ -2449,7 +2463,7 @@ static void force_qs_rnp(struct rcu_state *rsp,
 		for (; cpu <= rnp->grphi; cpu++, bit <<= 1) {
 			if ((rnp->qsmask & bit) != 0) {
 				if ((rnp->qsmaskinit & bit) != 0)
-					*isidle = 0;
+					*isidle = false;
 				if (f(per_cpu_ptr(rsp->rda, cpu), isidle, maxj))
 					mask |= bit;
 			}
@@ -2505,9 +2519,10 @@ static void force_quiescent_state(struct rcu_state *rsp)
 		raw_spin_unlock_irqrestore(&rnp_old->lock, flags);
 		return;  /* Someone beat us to it. */
 	}
-	ACCESS_ONCE(rsp->gp_flags) |= RCU_GP_FLAG_FQS;
+	ACCESS_ONCE(rsp->gp_flags) =
+		ACCESS_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS;
 	raw_spin_unlock_irqrestore(&rnp_old->lock, flags);
-	wake_up(&rsp->gp_wq);  /* Memory barrier implied by wake_up() path. */
+	rcu_gp_kthread_wake(rsp);
 }
 
 /*
@@ -2925,11 +2940,6 @@ static int synchronize_sched_expedited_cpu_stop(void *data)
  * restructure your code to batch your updates, and then use a single
  * synchronize_sched() instead.
  *
- * Note that it is illegal to call this function while holding any lock
- * that is acquired by a CPU-hotplug notifier.  And yes, it is also illegal
- * to call this function from a CPU-hotplug notifier.  Failing to observe
- * these restriction will result in deadlock.
- *
  * This implementation can be thought of as an application of ticket
  * locking to RCU, with sync_sched_expedited_started and
  * sync_sched_expedited_done taking on the roles of the halves
@@ -2979,7 +2989,12 @@ void synchronize_sched_expedited(void)
 	 */
 	snap = atomic_long_inc_return(&rsp->expedited_start);
 	firstsnap = snap;
-	get_online_cpus();
+	if (!try_get_online_cpus()) {
+		/* CPU hotplug operation in flight, fall back to normal GP. */
+		wait_rcu_gp(call_rcu_sched);
+		atomic_long_inc(&rsp->expedited_normal);
+		return;
+	}
 	WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id()));
 
 	/*
@@ -3026,7 +3041,12 @@ void synchronize_sched_expedited(void)
 		 * and they started after our first try, so their grace
 		 * period works for us.
 		 */
-		get_online_cpus();
+		if (!try_get_online_cpus()) {
+			/* CPU hotplug operation in flight, use normal GP. */
+			wait_rcu_gp(call_rcu_sched);
+			atomic_long_inc(&rsp->expedited_normal);
+			return;
+		}
 		snap = atomic_long_read(&rsp->expedited_start);
 		smp_mb(); /* ensure read is before try_stop_cpus(). */
 	}
@@ -3442,6 +3462,7 @@ static int rcu_cpu_notify(struct notifier_block *self,
 	case CPU_UP_PREPARE_FROZEN:
 		rcu_prepare_cpu(cpu);
 		rcu_prepare_kthreads(cpu);
+		rcu_spawn_all_nocb_kthreads(cpu);
 		break;
 	case CPU_ONLINE:
 	case CPU_DOWN_FAILED:
@@ -3489,7 +3510,7 @@ static int rcu_pm_notify(struct notifier_block *self,
 }
 
 /*
- * Spawn the kthread that handles this RCU flavor's grace periods.
+ * Spawn the kthreads that handle each RCU flavor's grace periods.
  */
 static int __init rcu_spawn_gp_kthread(void)
 {
@@ -3498,6 +3519,7 @@ static int __init rcu_spawn_gp_kthread(void)
 	struct rcu_state *rsp;
 	struct task_struct *t;
 
+	rcu_scheduler_fully_active = 1;
 	for_each_rcu_flavor(rsp) {
 		t = kthread_run(rcu_gp_kthread, rsp, "%s", rsp->name);
 		BUG_ON(IS_ERR(t));
@@ -3505,8 +3527,9 @@ static int __init rcu_spawn_gp_kthread(void)
 		raw_spin_lock_irqsave(&rnp->lock, flags);
 		rsp->gp_kthread = t;
 		raw_spin_unlock_irqrestore(&rnp->lock, flags);
-		rcu_spawn_nocb_kthreads(rsp);
 	}
+	rcu_spawn_nocb_kthreads();
+	rcu_spawn_boost_kthreads();
 	return 0;
 }
 early_initcall(rcu_spawn_gp_kthread);
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 6a86eb7bac45..d03764652d91 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -350,7 +350,7 @@ struct rcu_data {
 	int nocb_p_count_lazy;		/*  (approximate). */
 	wait_queue_head_t nocb_wq;	/* For nocb kthreads to sleep on. */
 	struct task_struct *nocb_kthread;
-	bool nocb_defer_wakeup;		/* Defer wakeup of nocb_kthread. */
+	int nocb_defer_wakeup;		/* Defer wakeup of nocb_kthread. */
 
 	/* The following fields are used by the leader, hence own cacheline. */
 	struct rcu_head *nocb_gp_head ____cacheline_internodealigned_in_smp;
@@ -383,6 +383,11 @@ struct rcu_data {
 #define RCU_FORCE_QS		3	/* Need to force quiescent state. */
 #define RCU_SIGNAL_INIT		RCU_SAVE_DYNTICK
 
+/* Values for nocb_defer_wakeup field in struct rcu_data. */
+#define RCU_NOGP_WAKE_NOT	0
+#define RCU_NOGP_WAKE		1
+#define RCU_NOGP_WAKE_FORCE	2
+
 #define RCU_JIFFIES_TILL_FORCE_QS (1 + (HZ > 250) + (HZ > 500))
 					/* For jiffies_till_first_fqs and */
 					/*  and jiffies_till_next_fqs. */
@@ -572,6 +577,7 @@ static void rcu_preempt_do_callbacks(void);
 static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
 						 struct rcu_node *rnp);
 #endif /* #ifdef CONFIG_RCU_BOOST */
+static void __init rcu_spawn_boost_kthreads(void);
 static void rcu_prepare_kthreads(int cpu);
 static void rcu_cleanup_after_idle(int cpu);
 static void rcu_prepare_for_idle(int cpu);
@@ -589,10 +595,14 @@ static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
 static bool rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
 				      struct rcu_data *rdp,
 				      unsigned long flags);
-static bool rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp);
+static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp);
 static void do_nocb_deferred_wakeup(struct rcu_data *rdp);
 static void rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp);
-static void rcu_spawn_nocb_kthreads(struct rcu_state *rsp);
+static void rcu_spawn_all_nocb_kthreads(int cpu);
+static void __init rcu_spawn_nocb_kthreads(void);
+#ifdef CONFIG_RCU_NOCB_CPU
+static void __init rcu_organize_nocb_kthreads(struct rcu_state *rsp);
+#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
 static void __maybe_unused rcu_kick_nohz_cpu(int cpu);
 static bool init_nocb_callback_list(struct rcu_data *rdp);
 static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq);
@@ -605,6 +615,8 @@ static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
 static void rcu_bind_gp_kthread(void);
 static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp);
 static bool rcu_nohz_full_cpu(struct rcu_state *rsp);
+static void rcu_dynticks_task_enter(void);
+static void rcu_dynticks_task_exit(void);
 
 #endif /* #ifndef RCU_TREE_NONCORE */
 
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index a7997e272564..387dd4599344 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -85,33 +85,6 @@ static void __init rcu_bootup_announce_oddness(void)
 		pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
 	if (nr_cpu_ids != NR_CPUS)
 		pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);
-#ifdef CONFIG_RCU_NOCB_CPU
-#ifndef CONFIG_RCU_NOCB_CPU_NONE
-	if (!have_rcu_nocb_mask) {
-		zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL);
-		have_rcu_nocb_mask = true;
-	}
-#ifdef CONFIG_RCU_NOCB_CPU_ZERO
-	pr_info("\tOffload RCU callbacks from CPU 0\n");
-	cpumask_set_cpu(0, rcu_nocb_mask);
-#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */
-#ifdef CONFIG_RCU_NOCB_CPU_ALL
-	pr_info("\tOffload RCU callbacks from all CPUs\n");
-	cpumask_copy(rcu_nocb_mask, cpu_possible_mask);
-#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */
-#endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */
-	if (have_rcu_nocb_mask) {
-		if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
-			pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n");
-			cpumask_and(rcu_nocb_mask, cpu_possible_mask,
-				    rcu_nocb_mask);
-		}
-		cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask);
-		pr_info("\tOffload RCU callbacks from CPUs: %s.\n", nocb_buf);
-		if (rcu_nocb_poll)
-			pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
-	}
-#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
 }
 
 #ifdef CONFIG_TREE_PREEMPT_RCU
@@ -134,7 +107,7 @@ static void __init rcu_bootup_announce(void)
  * Return the number of RCU-preempt batches processed thus far
  * for debug and statistics.
  */
-long rcu_batches_completed_preempt(void)
+static long rcu_batches_completed_preempt(void)
 {
 	return rcu_preempt_state.completed;
 }
@@ -155,18 +128,19 @@ EXPORT_SYMBOL_GPL(rcu_batches_completed);
  * not in a quiescent state.  There might be any number of tasks blocked
  * while in an RCU read-side critical section.
  *
- * Unlike the other rcu_*_qs() functions, callers to this function
- * must disable irqs in order to protect the assignment to
- * ->rcu_read_unlock_special.
- */
-static void rcu_preempt_qs(int cpu)
-{
-	struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
-
-	if (rdp->passed_quiesce == 0)
-		trace_rcu_grace_period(TPS("rcu_preempt"), rdp->gpnum, TPS("cpuqs"));
-	rdp->passed_quiesce = 1;
-	current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
+ * As with the other rcu_*_qs() functions, callers to this function
+ * must disable preemption.
+ */
+static void rcu_preempt_qs(void)
+{
+	if (!__this_cpu_read(rcu_preempt_data.passed_quiesce)) {
+		trace_rcu_grace_period(TPS("rcu_preempt"),
+				       __this_cpu_read(rcu_preempt_data.gpnum),
+				       TPS("cpuqs"));
+		__this_cpu_write(rcu_preempt_data.passed_quiesce, 1);
+		barrier(); /* Coordinate with rcu_preempt_check_callbacks(). */
+		current->rcu_read_unlock_special.b.need_qs = false;
+	}
 }
 
 /*
@@ -190,14 +164,14 @@ static void rcu_preempt_note_context_switch(int cpu)
 	struct rcu_node *rnp;
 
 	if (t->rcu_read_lock_nesting > 0 &&
-	    (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
+	    !t->rcu_read_unlock_special.b.blocked) {
 
 		/* Possibly blocking in an RCU read-side critical section. */
 		rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu);
 		rnp = rdp->mynode;
 		raw_spin_lock_irqsave(&rnp->lock, flags);
 		smp_mb__after_unlock_lock();
-		t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
+		t->rcu_read_unlock_special.b.blocked = true;
 		t->rcu_blocked_node = rnp;
 
 		/*
@@ -239,7 +213,7 @@ static void rcu_preempt_note_context_switch(int cpu)
 				       : rnp->gpnum + 1);
 		raw_spin_unlock_irqrestore(&rnp->lock, flags);
 	} else if (t->rcu_read_lock_nesting < 0 &&
-		   t->rcu_read_unlock_special) {
+		   t->rcu_read_unlock_special.s) {
 
 		/*
 		 * Complete exit from RCU read-side critical section on
@@ -257,9 +231,7 @@ static void rcu_preempt_note_context_switch(int cpu)
 	 * grace period, then the fact that the task has been enqueued
 	 * means that we continue to block the current grace period.
 	 */
-	local_irq_save(flags);
-	rcu_preempt_qs(cpu);
-	local_irq_restore(flags);
+	rcu_preempt_qs();
 }
 
 /*
@@ -340,7 +312,7 @@ void rcu_read_unlock_special(struct task_struct *t)
 	bool drop_boost_mutex = false;
 #endif /* #ifdef CONFIG_RCU_BOOST */
 	struct rcu_node *rnp;
-	int special;
+	union rcu_special special;
 
 	/* NMI handlers cannot block and cannot safely manipulate state. */
 	if (in_nmi())
@@ -350,12 +322,13 @@ void rcu_read_unlock_special(struct task_struct *t)
 
 	/*
 	 * If RCU core is waiting for this CPU to exit critical section,
-	 * let it know that we have done so.
+	 * let it know that we have done so.  Because irqs are disabled,
+	 * t->rcu_read_unlock_special cannot change.
 	 */
 	special = t->rcu_read_unlock_special;
-	if (special & RCU_READ_UNLOCK_NEED_QS) {
-		rcu_preempt_qs(smp_processor_id());
-		if (!t->rcu_read_unlock_special) {
+	if (special.b.need_qs) {
+		rcu_preempt_qs();
+		if (!t->rcu_read_unlock_special.s) {
 			local_irq_restore(flags);
 			return;
 		}
@@ -368,8 +341,8 @@ void rcu_read_unlock_special(struct task_struct *t)
 	}
 
 	/* Clean up if blocked during RCU read-side critical section. */
-	if (special & RCU_READ_UNLOCK_BLOCKED) {
-		t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
+	if (special.b.blocked) {
+		t->rcu_read_unlock_special.b.blocked = false;
 
 		/*
 		 * Remove this task from the list it blocked on.  The
@@ -653,12 +626,13 @@ static void rcu_preempt_check_callbacks(int cpu)
 	struct task_struct *t = current;
 
 	if (t->rcu_read_lock_nesting == 0) {
-		rcu_preempt_qs(cpu);
+		rcu_preempt_qs();
 		return;
 	}
 	if (t->rcu_read_lock_nesting > 0 &&
-	    per_cpu(rcu_preempt_data, cpu).qs_pending)
-		t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
+	    per_cpu(rcu_preempt_data, cpu).qs_pending &&
+	    !per_cpu(rcu_preempt_data, cpu).passed_quiesce)
+		t->rcu_read_unlock_special.b.need_qs = true;
 }
 
 #ifdef CONFIG_RCU_BOOST
@@ -819,11 +793,6 @@ sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
  * 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.
- *
- * Note that it is illegal to call this function while holding any lock
- * that is acquired by a CPU-hotplug notifier.  And yes, it is also illegal
- * to call this function from a CPU-hotplug notifier.  Failing to observe
- * these restriction will result in deadlock.
  */
 void synchronize_rcu_expedited(void)
 {
@@ -845,7 +814,11 @@ void synchronize_rcu_expedited(void)
 	 * being boosted.  This simplifies the process of moving tasks
 	 * from leaf to root rcu_node structures.
 	 */
-	get_online_cpus();
+	if (!try_get_online_cpus()) {
+		/* CPU-hotplug operation in flight, fall back to normal GP. */
+		wait_rcu_gp(call_rcu);
+		return;
+	}
 
 	/*
 	 * Acquire lock, falling back to synchronize_rcu() if too many
@@ -897,7 +870,8 @@ void synchronize_rcu_expedited(void)
 
 	/* Clean up and exit. */
 	smp_mb(); /* ensure expedited GP seen before counter increment. */
-	ACCESS_ONCE(sync_rcu_preempt_exp_count)++;
+	ACCESS_ONCE(sync_rcu_preempt_exp_count) =
+					sync_rcu_preempt_exp_count + 1;
 unlock_mb_ret:
 	mutex_unlock(&sync_rcu_preempt_exp_mutex);
 mb_ret:
@@ -941,7 +915,7 @@ void exit_rcu(void)
 		return;
 	t->rcu_read_lock_nesting = 1;
 	barrier();
-	t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED;
+	t->rcu_read_unlock_special.b.blocked = true;
 	__rcu_read_unlock();
 }
 
@@ -1462,14 +1436,13 @@ static struct smp_hotplug_thread rcu_cpu_thread_spec = {
 };
 
 /*
- * Spawn all kthreads -- called as soon as the scheduler is running.
+ * Spawn boost kthreads -- called as soon as the scheduler is running.
  */
-static int __init rcu_spawn_kthreads(void)
+static void __init rcu_spawn_boost_kthreads(void)
 {
 	struct rcu_node *rnp;
 	int cpu;
 
-	rcu_scheduler_fully_active = 1;
 	for_each_possible_cpu(cpu)
 		per_cpu(rcu_cpu_has_work, cpu) = 0;
 	BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
@@ -1479,9 +1452,7 @@ static int __init rcu_spawn_kthreads(void)
 		rcu_for_each_leaf_node(rcu_state_p, rnp)
 			(void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
 	}
-	return 0;
 }
-early_initcall(rcu_spawn_kthreads);
 
 static void rcu_prepare_kthreads(int cpu)
 {
@@ -1519,12 +1490,9 @@ static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
 {
 }
 
-static int __init rcu_scheduler_really_started(void)
+static void __init rcu_spawn_boost_kthreads(void)
 {
-	rcu_scheduler_fully_active = 1;
-	return 0;
 }
-early_initcall(rcu_scheduler_really_started);
 
 static void rcu_prepare_kthreads(int cpu)
 {
@@ -1625,7 +1593,7 @@ static bool __maybe_unused rcu_try_advance_all_cbs(void)
 
 	/* Exit early if we advanced recently. */
 	if (jiffies == rdtp->last_advance_all)
-		return 0;
+		return false;
 	rdtp->last_advance_all = jiffies;
 
 	for_each_rcu_flavor(rsp) {
@@ -1848,7 +1816,7 @@ static int rcu_oom_notify(struct notifier_block *self,
 	get_online_cpus();
 	for_each_online_cpu(cpu) {
 		smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
-		cond_resched();
+		cond_resched_rcu_qs();
 	}
 	put_online_cpus();
 
@@ -2075,7 +2043,7 @@ static void wake_nocb_leader(struct rcu_data *rdp, bool force)
 	if (!ACCESS_ONCE(rdp_leader->nocb_kthread))
 		return;
 	if (ACCESS_ONCE(rdp_leader->nocb_leader_sleep) || force) {
-		/* Prior xchg orders against prior callback enqueue. */
+		/* Prior smp_mb__after_atomic() orders against prior enqueue. */
 		ACCESS_ONCE(rdp_leader->nocb_leader_sleep) = false;
 		wake_up(&rdp_leader->nocb_wq);
 	}
@@ -2104,6 +2072,7 @@ static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
 	ACCESS_ONCE(*old_rhpp) = rhp;
 	atomic_long_add(rhcount, &rdp->nocb_q_count);
 	atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy);
+	smp_mb__after_atomic(); /* Store *old_rhpp before _wake test. */
 
 	/* If we are not being polled and there is a kthread, awaken it ... */
 	t = ACCESS_ONCE(rdp->nocb_kthread);
@@ -2120,16 +2089,23 @@ static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
 			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
 					    TPS("WakeEmpty"));
 		} else {
-			rdp->nocb_defer_wakeup = true;
+			rdp->nocb_defer_wakeup = RCU_NOGP_WAKE;
 			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
 					    TPS("WakeEmptyIsDeferred"));
 		}
 		rdp->qlen_last_fqs_check = 0;
 	} else if (len > rdp->qlen_last_fqs_check + qhimark) {
 		/* ... or if many callbacks queued. */
-		wake_nocb_leader(rdp, true);
+		if (!irqs_disabled_flags(flags)) {
+			wake_nocb_leader(rdp, true);
+			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+					    TPS("WakeOvf"));
+		} else {
+			rdp->nocb_defer_wakeup = RCU_NOGP_WAKE_FORCE;
+			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+					    TPS("WakeOvfIsDeferred"));
+		}
 		rdp->qlen_last_fqs_check = LONG_MAX / 2;
-		trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeOvf"));
 	} else {
 		trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot"));
 	}
@@ -2150,7 +2126,7 @@ static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
 {
 
 	if (!rcu_is_nocb_cpu(rdp->cpu))
-		return 0;
+		return false;
 	__call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy, flags);
 	if (__is_kfree_rcu_offset((unsigned long)rhp->func))
 		trace_rcu_kfree_callback(rdp->rsp->name, rhp,
@@ -2161,7 +2137,18 @@ static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
 		trace_rcu_callback(rdp->rsp->name, rhp,
 				   -atomic_long_read(&rdp->nocb_q_count_lazy),
 				   -atomic_long_read(&rdp->nocb_q_count));
-	return 1;
+
+	/*
+	 * If called from an extended quiescent state with interrupts
+	 * disabled, invoke the RCU core in order to allow the idle-entry
+	 * deferred-wakeup check to function.
+	 */
+	if (irqs_disabled_flags(flags) &&
+	    !rcu_is_watching() &&
+	    cpu_online(smp_processor_id()))
+		invoke_rcu_core();
+
+	return true;
 }
 
 /*
@@ -2177,7 +2164,7 @@ static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
 
 	/* If this is not a no-CBs CPU, tell the caller to do it the old way. */
 	if (!rcu_is_nocb_cpu(smp_processor_id()))
-		return 0;
+		return false;
 	rsp->qlen = 0;
 	rsp->qlen_lazy = 0;
 
@@ -2196,7 +2183,7 @@ static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
 		rsp->orphan_nxtlist = NULL;
 		rsp->orphan_nxttail = &rsp->orphan_nxtlist;
 	}
-	return 1;
+	return true;
 }
 
 /*
@@ -2229,7 +2216,7 @@ static void rcu_nocb_wait_gp(struct rcu_data *rdp)
 			(d = ULONG_CMP_GE(ACCESS_ONCE(rnp->completed), c)));
 		if (likely(d))
 			break;
-		flush_signals(current);
+		WARN_ON(signal_pending(current));
 		trace_rcu_future_gp(rnp, rdp, c, TPS("ResumeWait"));
 	}
 	trace_rcu_future_gp(rnp, rdp, c, TPS("EndWait"));
@@ -2288,7 +2275,7 @@ wait_again:
 		if (!rcu_nocb_poll)
 			trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu,
 					    "WokeEmpty");
-		flush_signals(current);
+		WARN_ON(signal_pending(current));
 		schedule_timeout_interruptible(1);
 
 		/* Rescan in case we were a victim of memory ordering. */
@@ -2327,6 +2314,7 @@ wait_again:
 		atomic_long_add(rdp->nocb_gp_count, &rdp->nocb_follower_count);
 		atomic_long_add(rdp->nocb_gp_count_lazy,
 				&rdp->nocb_follower_count_lazy);
+		smp_mb__after_atomic(); /* Store *tail before wakeup. */
 		if (rdp != my_rdp && tail == &rdp->nocb_follower_head) {
 			/*
 			 * List was empty, wake up the follower.
@@ -2367,7 +2355,7 @@ static void nocb_follower_wait(struct rcu_data *rdp)
 		if (!rcu_nocb_poll)
 			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
 					    "WokeEmpty");
-		flush_signals(current);
+		WARN_ON(signal_pending(current));
 		schedule_timeout_interruptible(1);
 	}
 }
@@ -2428,15 +2416,16 @@ static int rcu_nocb_kthread(void *arg)
 			list = next;
 		}
 		trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1);
-		ACCESS_ONCE(rdp->nocb_p_count) -= c;
-		ACCESS_ONCE(rdp->nocb_p_count_lazy) -= cl;
+		ACCESS_ONCE(rdp->nocb_p_count) = rdp->nocb_p_count - c;
+		ACCESS_ONCE(rdp->nocb_p_count_lazy) =
+						rdp->nocb_p_count_lazy - cl;
 		rdp->n_nocbs_invoked += c;
 	}
 	return 0;
 }
 
 /* Is a deferred wakeup of rcu_nocb_kthread() required? */
-static bool rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
+static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
 {
 	return ACCESS_ONCE(rdp->nocb_defer_wakeup);
 }
@@ -2444,11 +2433,79 @@ static bool rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
 /* Do a deferred wakeup of rcu_nocb_kthread(). */
 static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
 {
+	int ndw;
+
 	if (!rcu_nocb_need_deferred_wakeup(rdp))
 		return;
-	ACCESS_ONCE(rdp->nocb_defer_wakeup) = false;
-	wake_nocb_leader(rdp, false);
-	trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("DeferredWakeEmpty"));
+	ndw = ACCESS_ONCE(rdp->nocb_defer_wakeup);
+	ACCESS_ONCE(rdp->nocb_defer_wakeup) = RCU_NOGP_WAKE_NOT;
+	wake_nocb_leader(rdp, ndw == RCU_NOGP_WAKE_FORCE);
+	trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("DeferredWake"));
+}
+
+void __init rcu_init_nohz(void)
+{
+	int cpu;
+	bool need_rcu_nocb_mask = true;
+	struct rcu_state *rsp;
+
+#ifdef CONFIG_RCU_NOCB_CPU_NONE
+	need_rcu_nocb_mask = false;
+#endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */
+
+#if defined(CONFIG_NO_HZ_FULL)
+	if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask))
+		need_rcu_nocb_mask = true;
+#endif /* #if defined(CONFIG_NO_HZ_FULL) */
+
+	if (!have_rcu_nocb_mask && need_rcu_nocb_mask) {
+		if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
+			pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
+			return;
+		}
+		have_rcu_nocb_mask = true;
+	}
+	if (!have_rcu_nocb_mask)
+		return;
+
+#ifdef CONFIG_RCU_NOCB_CPU_ZERO
+	pr_info("\tOffload RCU callbacks from CPU 0\n");
+	cpumask_set_cpu(0, rcu_nocb_mask);
+#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */
+#ifdef CONFIG_RCU_NOCB_CPU_ALL
+	pr_info("\tOffload RCU callbacks from all CPUs\n");
+	cpumask_copy(rcu_nocb_mask, cpu_possible_mask);
+#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */
+#if defined(CONFIG_NO_HZ_FULL)
+	if (tick_nohz_full_running)
+		cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
+#endif /* #if defined(CONFIG_NO_HZ_FULL) */
+
+	if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
+		pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n");
+		cpumask_and(rcu_nocb_mask, cpu_possible_mask,
+			    rcu_nocb_mask);
+	}
+	cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask);
+	pr_info("\tOffload RCU callbacks from CPUs: %s.\n", nocb_buf);
+	if (rcu_nocb_poll)
+		pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
+
+	for_each_rcu_flavor(rsp) {
+		for_each_cpu(cpu, rcu_nocb_mask) {
+			struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
+
+			/*
+			 * If there are early callbacks, they will need
+			 * to be moved to the nocb lists.
+			 */
+			WARN_ON_ONCE(rdp->nxttail[RCU_NEXT_TAIL] !=
+				     &rdp->nxtlist &&
+				     rdp->nxttail[RCU_NEXT_TAIL] != NULL);
+			init_nocb_callback_list(rdp);
+		}
+		rcu_organize_nocb_kthreads(rsp);
+	}
 }
 
 /* Initialize per-rcu_data variables for no-CBs CPUs. */
@@ -2459,15 +2516,85 @@ static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
 	rdp->nocb_follower_tail = &rdp->nocb_follower_head;
 }
 
+/*
+ * If the specified CPU is a no-CBs CPU that does not already have its
+ * rcuo kthread for the specified RCU flavor, spawn it.  If the CPUs are
+ * brought online out of order, this can require re-organizing the
+ * leader-follower relationships.
+ */
+static void rcu_spawn_one_nocb_kthread(struct rcu_state *rsp, int cpu)
+{
+	struct rcu_data *rdp;
+	struct rcu_data *rdp_last;
+	struct rcu_data *rdp_old_leader;
+	struct rcu_data *rdp_spawn = per_cpu_ptr(rsp->rda, cpu);
+	struct task_struct *t;
+
+	/*
+	 * If this isn't a no-CBs CPU or if it already has an rcuo kthread,
+	 * then nothing to do.
+	 */
+	if (!rcu_is_nocb_cpu(cpu) || rdp_spawn->nocb_kthread)
+		return;
+
+	/* If we didn't spawn the leader first, reorganize! */
+	rdp_old_leader = rdp_spawn->nocb_leader;
+	if (rdp_old_leader != rdp_spawn && !rdp_old_leader->nocb_kthread) {
+		rdp_last = NULL;
+		rdp = rdp_old_leader;
+		do {
+			rdp->nocb_leader = rdp_spawn;
+			if (rdp_last && rdp != rdp_spawn)
+				rdp_last->nocb_next_follower = rdp;
+			rdp_last = rdp;
+			rdp = rdp->nocb_next_follower;
+			rdp_last->nocb_next_follower = NULL;
+		} while (rdp);
+		rdp_spawn->nocb_next_follower = rdp_old_leader;
+	}
+
+	/* Spawn the kthread for this CPU and RCU flavor. */
+	t = kthread_run(rcu_nocb_kthread, rdp_spawn,
+			"rcuo%c/%d", rsp->abbr, cpu);
+	BUG_ON(IS_ERR(t));
+	ACCESS_ONCE(rdp_spawn->nocb_kthread) = t;
+}
+
+/*
+ * If the specified CPU is a no-CBs CPU that does not already have its
+ * rcuo kthreads, spawn them.
+ */
+static void rcu_spawn_all_nocb_kthreads(int cpu)
+{
+	struct rcu_state *rsp;
+
+	if (rcu_scheduler_fully_active)
+		for_each_rcu_flavor(rsp)
+			rcu_spawn_one_nocb_kthread(rsp, cpu);
+}
+
+/*
+ * Once the scheduler is running, spawn rcuo kthreads for all online
+ * no-CBs CPUs.  This assumes that the early_initcall()s happen before
+ * non-boot CPUs come online -- if this changes, we will need to add
+ * some mutual exclusion.
+ */
+static void __init rcu_spawn_nocb_kthreads(void)
+{
+	int cpu;
+
+	for_each_online_cpu(cpu)
+		rcu_spawn_all_nocb_kthreads(cpu);
+}
+
 /* How many follower CPU IDs per leader?  Default of -1 for sqrt(nr_cpu_ids). */
 static int rcu_nocb_leader_stride = -1;
 module_param(rcu_nocb_leader_stride, int, 0444);
 
 /*
- * Create a kthread for each RCU flavor for each no-CBs CPU.
- * Also initialize leader-follower relationships.
+ * Initialize leader-follower relationships for all no-CBs CPU.
  */
-static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
+static void __init rcu_organize_nocb_kthreads(struct rcu_state *rsp)
 {
 	int cpu;
 	int ls = rcu_nocb_leader_stride;
@@ -2475,14 +2602,9 @@ static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
 	struct rcu_data *rdp;
 	struct rcu_data *rdp_leader = NULL;  /* Suppress misguided gcc warn. */
 	struct rcu_data *rdp_prev = NULL;
-	struct task_struct *t;
 
-	if (rcu_nocb_mask == NULL)
+	if (!have_rcu_nocb_mask)
 		return;
-#if defined(CONFIG_NO_HZ_FULL) && !defined(CONFIG_NO_HZ_FULL_ALL)
-	if (tick_nohz_full_running)
-		cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
-#endif /* #if defined(CONFIG_NO_HZ_FULL) && !defined(CONFIG_NO_HZ_FULL_ALL) */
 	if (ls == -1) {
 		ls = int_sqrt(nr_cpu_ids);
 		rcu_nocb_leader_stride = ls;
@@ -2505,21 +2627,15 @@ static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
 			rdp_prev->nocb_next_follower = rdp;
 		}
 		rdp_prev = rdp;
-
-		/* Spawn the kthread for this CPU. */
-		t = kthread_run(rcu_nocb_kthread, rdp,
-				"rcuo%c/%d", rsp->abbr, cpu);
-		BUG_ON(IS_ERR(t));
-		ACCESS_ONCE(rdp->nocb_kthread) = t;
 	}
 }
 
 /* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
 static bool init_nocb_callback_list(struct rcu_data *rdp)
 {
-	if (rcu_nocb_mask == NULL ||
-	    !cpumask_test_cpu(rdp->cpu, rcu_nocb_mask))
+	if (!rcu_is_nocb_cpu(rdp->cpu))
 		return false;
+
 	rdp->nxttail[RCU_NEXT_TAIL] = NULL;
 	return true;
 }
@@ -2541,21 +2657,21 @@ static void rcu_init_one_nocb(struct rcu_node *rnp)
 static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
 			    bool lazy, unsigned long flags)
 {
-	return 0;
+	return false;
 }
 
 static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
 						     struct rcu_data *rdp,
 						     unsigned long flags)
 {
-	return 0;
+	return false;
 }
 
 static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
 {
 }
 
-static bool rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
+static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
 {
 	return false;
 }
@@ -2564,7 +2680,11 @@ static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
 {
 }
 
-static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
+static void rcu_spawn_all_nocb_kthreads(int cpu)
+{
+}
+
+static void __init rcu_spawn_nocb_kthreads(void)
 {
 }
 
@@ -2595,16 +2715,6 @@ static void __maybe_unused rcu_kick_nohz_cpu(int cpu)
 
 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
 
-/*
- * Define RCU flavor that holds sysidle state.  This needs to be the
- * most active flavor of RCU.
- */
-#ifdef CONFIG_PREEMPT_RCU
-static struct rcu_state *rcu_sysidle_state = &rcu_preempt_state;
-#else /* #ifdef CONFIG_PREEMPT_RCU */
-static struct rcu_state *rcu_sysidle_state = &rcu_sched_state;
-#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
-
 static int full_sysidle_state;		/* Current system-idle state. */
 #define RCU_SYSIDLE_NOT		0	/* Some CPU is not idle. */
 #define RCU_SYSIDLE_SHORT	1	/* All CPUs idle for brief period. */
@@ -2622,6 +2732,10 @@ static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq)
 {
 	unsigned long j;
 
+	/* If there are no nohz_full= CPUs, no need to track this. */
+	if (!tick_nohz_full_enabled())
+		return;
+
 	/* Adjust nesting, check for fully idle. */
 	if (irq) {
 		rdtp->dynticks_idle_nesting--;
@@ -2687,6 +2801,10 @@ void rcu_sysidle_force_exit(void)
  */
 static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq)
 {
+	/* If there are no nohz_full= CPUs, no need to track this. */
+	if (!tick_nohz_full_enabled())
+		return;
+
 	/* Adjust nesting, check for already non-idle. */
 	if (irq) {
 		rdtp->dynticks_idle_nesting++;
@@ -2741,12 +2859,16 @@ static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
 	unsigned long j;
 	struct rcu_dynticks *rdtp = rdp->dynticks;
 
+	/* If there are no nohz_full= CPUs, don't check system-wide idleness. */
+	if (!tick_nohz_full_enabled())
+		return;
+
 	/*
 	 * If some other CPU has already reported non-idle, if this is
 	 * not the flavor of RCU that tracks sysidle state, or if this
 	 * is an offline or the timekeeping CPU, nothing to do.
 	 */
-	if (!*isidle || rdp->rsp != rcu_sysidle_state ||
+	if (!*isidle || rdp->rsp != rcu_state_p ||
 	    cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu)
 		return;
 	if (rcu_gp_in_progress(rdp->rsp))
@@ -2772,7 +2894,7 @@ static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
  */
 static bool is_sysidle_rcu_state(struct rcu_state *rsp)
 {
-	return rsp == rcu_sysidle_state;
+	return rsp == rcu_state_p;
 }
 
 /*
@@ -2850,7 +2972,7 @@ static void rcu_sysidle_cancel(void)
 static void rcu_sysidle_report(struct rcu_state *rsp, int isidle,
 			       unsigned long maxj, bool gpkt)
 {
-	if (rsp != rcu_sysidle_state)
+	if (rsp != rcu_state_p)
 		return;  /* Wrong flavor, ignore. */
 	if (gpkt && nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
 		return;  /* Running state machine from timekeeping CPU. */
@@ -2867,6 +2989,10 @@ static void rcu_sysidle_report(struct rcu_state *rsp, int isidle,
 static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
 				  unsigned long maxj)
 {
+	/* If there are no nohz_full= CPUs, no need to track this. */
+	if (!tick_nohz_full_enabled())
+		return;
+
 	rcu_sysidle_report(rsp, isidle, maxj, true);
 }
 
@@ -2893,7 +3019,8 @@ static void rcu_sysidle_cb(struct rcu_head *rhp)
 
 /*
  * Check to see if the system is fully idle, other than the timekeeping CPU.
- * The caller must have disabled interrupts.
+ * The caller must have disabled interrupts.  This is not intended to be
+ * called unless tick_nohz_full_enabled().
  */
 bool rcu_sys_is_idle(void)
 {
@@ -2919,13 +3046,12 @@ bool rcu_sys_is_idle(void)
 
 			/* Scan all the CPUs looking for nonidle CPUs. */
 			for_each_possible_cpu(cpu) {
-				rdp = per_cpu_ptr(rcu_sysidle_state->rda, cpu);
+				rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
 				rcu_sysidle_check_cpu(rdp, &isidle, &maxj);
 				if (!isidle)
 					break;
 			}
-			rcu_sysidle_report(rcu_sysidle_state,
-					   isidle, maxj, false);
+			rcu_sysidle_report(rcu_state_p, isidle, maxj, false);
 			oldrss = rss;
 			rss = ACCESS_ONCE(full_sysidle_state);
 		}
@@ -2952,7 +3078,7 @@ bool rcu_sys_is_idle(void)
 	 * provided by the memory allocator.
 	 */
 	if (nr_cpu_ids > CONFIG_NO_HZ_FULL_SYSIDLE_SMALL &&
-	    !rcu_gp_in_progress(rcu_sysidle_state) &&
+	    !rcu_gp_in_progress(rcu_state_p) &&
 	    !rsh.inuse && xchg(&rsh.inuse, 1) == 0)
 		call_rcu(&rsh.rh, rcu_sysidle_cb);
 	return false;
@@ -3036,3 +3162,19 @@ static void rcu_bind_gp_kthread(void)
 		housekeeping_affine(current);
 #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
 }
+
+/* Record the current task on dyntick-idle entry. */
+static void rcu_dynticks_task_enter(void)
+{
+#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
+	ACCESS_ONCE(current->rcu_tasks_idle_cpu) = smp_processor_id();
+#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
+}
+
+/* Record no current task on dyntick-idle exit. */
+static void rcu_dynticks_task_exit(void)
+{
+#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
+	ACCESS_ONCE(current->rcu_tasks_idle_cpu) = -1;
+#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
+}
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 4056d7992a6c..3ef8ba58694e 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -47,6 +47,8 @@
 #include <linux/hardirq.h>
 #include <linux/delay.h>
 #include <linux/module.h>
+#include <linux/kthread.h>
+#include <linux/tick.h>
 
 #define CREATE_TRACE_POINTS
 
@@ -91,7 +93,7 @@ void __rcu_read_unlock(void)
 		barrier();  /* critical section before exit code. */
 		t->rcu_read_lock_nesting = INT_MIN;
 		barrier();  /* assign before ->rcu_read_unlock_special load */
-		if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
+		if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special.s)))
 			rcu_read_unlock_special(t);
 		barrier();  /* ->rcu_read_unlock_special load before assign */
 		t->rcu_read_lock_nesting = 0;
@@ -137,6 +139,38 @@ int notrace debug_lockdep_rcu_enabled(void)
 EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
 
 /**
+ * rcu_read_lock_held() - might we be in RCU read-side critical section?
+ *
+ * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU
+ * read-side critical section.  In absence of CONFIG_DEBUG_LOCK_ALLOC,
+ * this assumes we are in an RCU read-side critical section unless it can
+ * prove otherwise.  This is useful for debug checks in functions that
+ * require that they be called within an RCU read-side critical section.
+ *
+ * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
+ * and while lockdep is disabled.
+ *
+ * Note that rcu_read_lock() and the matching rcu_read_unlock() must
+ * occur in the same context, for example, it is illegal to invoke
+ * rcu_read_unlock() in process context if the matching rcu_read_lock()
+ * was invoked from within an irq handler.
+ *
+ * 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_held(void)
+{
+	if (!debug_lockdep_rcu_enabled())
+		return 1;
+	if (!rcu_is_watching())
+		return 0;
+	if (!rcu_lockdep_current_cpu_online())
+		return 0;
+	return lock_is_held(&rcu_lock_map);
+}
+EXPORT_SYMBOL_GPL(rcu_read_lock_held);
+
+/**
  * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
  *
  * Check for bottom half being disabled, which covers both the
@@ -347,3 +381,312 @@ static int __init check_cpu_stall_init(void)
 early_initcall(check_cpu_stall_init);
 
 #endif /* #ifdef CONFIG_RCU_STALL_COMMON */
+
+#ifdef CONFIG_TASKS_RCU
+
+/*
+ * Simple variant of RCU whose quiescent states are voluntary context switch,
+ * user-space execution, and idle.  As such, grace periods can take one good
+ * long time.  There are no read-side primitives similar to rcu_read_lock()
+ * and rcu_read_unlock() because this implementation is intended to get
+ * the system into a safe state for some of the manipulations involved in
+ * tracing and the like.  Finally, this implementation does not support
+ * high call_rcu_tasks() rates from multiple CPUs.  If this is required,
+ * per-CPU callback lists will be needed.
+ */
+
+/* Global list of callbacks and associated lock. */
+static struct rcu_head *rcu_tasks_cbs_head;
+static struct rcu_head **rcu_tasks_cbs_tail = &rcu_tasks_cbs_head;
+static DECLARE_WAIT_QUEUE_HEAD(rcu_tasks_cbs_wq);
+static DEFINE_RAW_SPINLOCK(rcu_tasks_cbs_lock);
+
+/* Track exiting tasks in order to allow them to be waited for. */
+DEFINE_SRCU(tasks_rcu_exit_srcu);
+
+/* Control stall timeouts.  Disable with <= 0, otherwise jiffies till stall. */
+static int rcu_task_stall_timeout __read_mostly = HZ * 60 * 10;
+module_param(rcu_task_stall_timeout, int, 0644);
+
+static void rcu_spawn_tasks_kthread(void);
+
+/*
+ * Post an RCU-tasks callback.  First call must be from process context
+ * after the scheduler if fully operational.
+ */
+void call_rcu_tasks(struct rcu_head *rhp, void (*func)(struct rcu_head *rhp))
+{
+	unsigned long flags;
+	bool needwake;
+
+	rhp->next = NULL;
+	rhp->func = func;
+	raw_spin_lock_irqsave(&rcu_tasks_cbs_lock, flags);
+	needwake = !rcu_tasks_cbs_head;
+	*rcu_tasks_cbs_tail = rhp;
+	rcu_tasks_cbs_tail = &rhp->next;
+	raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags);
+	if (needwake) {
+		rcu_spawn_tasks_kthread();
+		wake_up(&rcu_tasks_cbs_wq);
+	}
+}
+EXPORT_SYMBOL_GPL(call_rcu_tasks);
+
+/**
+ * synchronize_rcu_tasks - wait until an rcu-tasks grace period has elapsed.
+ *
+ * Control will return to the caller some time after a full rcu-tasks
+ * grace period has elapsed, in other words after all currently
+ * executing rcu-tasks read-side critical sections have elapsed.  These
+ * read-side critical sections are delimited by calls to schedule(),
+ * cond_resched_rcu_qs(), idle execution, userspace execution, calls
+ * to synchronize_rcu_tasks(), and (in theory, anyway) cond_resched().
+ *
+ * This is a very specialized primitive, intended only for a few uses in
+ * tracing and other situations requiring manipulation of function
+ * preambles and profiling hooks.  The synchronize_rcu_tasks() function
+ * is not (yet) intended for heavy use from multiple CPUs.
+ *
+ * Note that this guarantee implies further memory-ordering guarantees.
+ * On systems with more than one CPU, when synchronize_rcu_tasks() returns,
+ * each CPU is guaranteed to have executed a full memory barrier since the
+ * end of its last RCU-tasks read-side critical section whose beginning
+ * preceded the call to synchronize_rcu_tasks().  In addition, each CPU
+ * having an RCU-tasks read-side critical section that extends beyond
+ * the return from synchronize_rcu_tasks() is guaranteed to have executed
+ * a full memory barrier after the beginning of synchronize_rcu_tasks()
+ * and before the beginning of that RCU-tasks read-side critical section.
+ * Note that these guarantees include CPUs that are offline, idle, or
+ * executing in user mode, as well as CPUs that are executing in the kernel.
+ *
+ * Furthermore, if CPU A invoked synchronize_rcu_tasks(), which returned
+ * to its caller on CPU B, then both CPU A and CPU B are guaranteed
+ * to have executed a full memory barrier during the execution of
+ * synchronize_rcu_tasks() -- even if CPU A and CPU B are the same CPU
+ * (but again only if the system has more than one CPU).
+ */
+void synchronize_rcu_tasks(void)
+{
+	/* Complain if the scheduler has not started.  */
+	rcu_lockdep_assert(!rcu_scheduler_active,
+			   "synchronize_rcu_tasks called too soon");
+
+	/* Wait for the grace period. */
+	wait_rcu_gp(call_rcu_tasks);
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu_tasks);
+
+/**
+ * rcu_barrier_tasks - Wait for in-flight call_rcu_tasks() callbacks.
+ *
+ * Although the current implementation is guaranteed to wait, it is not
+ * obligated to, for example, if there are no pending callbacks.
+ */
+void rcu_barrier_tasks(void)
+{
+	/* There is only one callback queue, so this is easy.  ;-) */
+	synchronize_rcu_tasks();
+}
+EXPORT_SYMBOL_GPL(rcu_barrier_tasks);
+
+/* See if tasks are still holding out, complain if so. */
+static void check_holdout_task(struct task_struct *t,
+			       bool needreport, bool *firstreport)
+{
+	int cpu;
+
+	if (!ACCESS_ONCE(t->rcu_tasks_holdout) ||
+	    t->rcu_tasks_nvcsw != ACCESS_ONCE(t->nvcsw) ||
+	    !ACCESS_ONCE(t->on_rq) ||
+	    (IS_ENABLED(CONFIG_NO_HZ_FULL) &&
+	     !is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) {
+		ACCESS_ONCE(t->rcu_tasks_holdout) = false;
+		list_del_init(&t->rcu_tasks_holdout_list);
+		put_task_struct(t);
+		return;
+	}
+	if (!needreport)
+		return;
+	if (*firstreport) {
+		pr_err("INFO: rcu_tasks detected stalls on tasks:\n");
+		*firstreport = false;
+	}
+	cpu = task_cpu(t);
+	pr_alert("%p: %c%c nvcsw: %lu/%lu holdout: %d idle_cpu: %d/%d\n",
+		 t, ".I"[is_idle_task(t)],
+		 "N."[cpu < 0 || !tick_nohz_full_cpu(cpu)],
+		 t->rcu_tasks_nvcsw, t->nvcsw, t->rcu_tasks_holdout,
+		 t->rcu_tasks_idle_cpu, cpu);
+	sched_show_task(t);
+}
+
+/* RCU-tasks kthread that detects grace periods and invokes callbacks. */
+static int __noreturn rcu_tasks_kthread(void *arg)
+{
+	unsigned long flags;
+	struct task_struct *g, *t;
+	unsigned long lastreport;
+	struct rcu_head *list;
+	struct rcu_head *next;
+	LIST_HEAD(rcu_tasks_holdouts);
+
+	/* FIXME: Add housekeeping affinity. */
+
+	/*
+	 * Each pass through the following loop makes one check for
+	 * newly arrived callbacks, and, if there are some, waits for
+	 * one RCU-tasks grace period and then invokes the callbacks.
+	 * This loop is terminated by the system going down.  ;-)
+	 */
+	for (;;) {
+
+		/* Pick up any new callbacks. */
+		raw_spin_lock_irqsave(&rcu_tasks_cbs_lock, flags);
+		list = rcu_tasks_cbs_head;
+		rcu_tasks_cbs_head = NULL;
+		rcu_tasks_cbs_tail = &rcu_tasks_cbs_head;
+		raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags);
+
+		/* If there were none, wait a bit and start over. */
+		if (!list) {
+			wait_event_interruptible(rcu_tasks_cbs_wq,
+						 rcu_tasks_cbs_head);
+			if (!rcu_tasks_cbs_head) {
+				WARN_ON(signal_pending(current));
+				schedule_timeout_interruptible(HZ/10);
+			}
+			continue;
+		}
+
+		/*
+		 * Wait for all pre-existing t->on_rq and t->nvcsw
+		 * transitions to complete.  Invoking synchronize_sched()
+		 * suffices because all these transitions occur with
+		 * interrupts disabled.  Without this synchronize_sched(),
+		 * a read-side critical section that started before the
+		 * grace period might be incorrectly seen as having started
+		 * after the grace period.
+		 *
+		 * This synchronize_sched() also dispenses with the
+		 * need for a memory barrier on the first store to
+		 * ->rcu_tasks_holdout, as it forces the store to happen
+		 * after the beginning of the grace period.
+		 */
+		synchronize_sched();
+
+		/*
+		 * There were callbacks, so we need to wait for an
+		 * RCU-tasks grace period.  Start off by scanning
+		 * the task list for tasks that are not already
+		 * voluntarily blocked.  Mark these tasks and make
+		 * a list of them in rcu_tasks_holdouts.
+		 */
+		rcu_read_lock();
+		for_each_process_thread(g, t) {
+			if (t != current && ACCESS_ONCE(t->on_rq) &&
+			    !is_idle_task(t)) {
+				get_task_struct(t);
+				t->rcu_tasks_nvcsw = ACCESS_ONCE(t->nvcsw);
+				ACCESS_ONCE(t->rcu_tasks_holdout) = true;
+				list_add(&t->rcu_tasks_holdout_list,
+					 &rcu_tasks_holdouts);
+			}
+		}
+		rcu_read_unlock();
+
+		/*
+		 * Wait for tasks that are in the process of exiting.
+		 * This does only part of the job, ensuring that all
+		 * tasks that were previously exiting reach the point
+		 * where they have disabled preemption, allowing the
+		 * later synchronize_sched() to finish the job.
+		 */
+		synchronize_srcu(&tasks_rcu_exit_srcu);
+
+		/*
+		 * Each pass through the following loop scans the list
+		 * of holdout tasks, removing any that are no longer
+		 * holdouts.  When the list is empty, we are done.
+		 */
+		lastreport = jiffies;
+		while (!list_empty(&rcu_tasks_holdouts)) {
+			bool firstreport;
+			bool needreport;
+			int rtst;
+			struct task_struct *t1;
+
+			schedule_timeout_interruptible(HZ);
+			rtst = ACCESS_ONCE(rcu_task_stall_timeout);
+			needreport = rtst > 0 &&
+				     time_after(jiffies, lastreport + rtst);
+			if (needreport)
+				lastreport = jiffies;
+			firstreport = true;
+			WARN_ON(signal_pending(current));
+			list_for_each_entry_safe(t, t1, &rcu_tasks_holdouts,
+						rcu_tasks_holdout_list) {
+				check_holdout_task(t, needreport, &firstreport);
+				cond_resched();
+			}
+		}
+
+		/*
+		 * Because ->on_rq and ->nvcsw are not guaranteed
+		 * to have a full memory barriers prior to them in the
+		 * schedule() path, memory reordering on other CPUs could
+		 * cause their RCU-tasks read-side critical sections to
+		 * extend past the end of the grace period.  However,
+		 * because these ->nvcsw updates are carried out with
+		 * interrupts disabled, we can use synchronize_sched()
+		 * to force the needed ordering on all such CPUs.
+		 *
+		 * This synchronize_sched() also confines all
+		 * ->rcu_tasks_holdout accesses to be within the grace
+		 * period, avoiding the need for memory barriers for
+		 * ->rcu_tasks_holdout accesses.
+		 *
+		 * In addition, this synchronize_sched() waits for exiting
+		 * tasks to complete their final preempt_disable() region
+		 * of execution, cleaning up after the synchronize_srcu()
+		 * above.
+		 */
+		synchronize_sched();
+
+		/* Invoke the callbacks. */
+		while (list) {
+			next = list->next;
+			local_bh_disable();
+			list->func(list);
+			local_bh_enable();
+			list = next;
+			cond_resched();
+		}
+		schedule_timeout_uninterruptible(HZ/10);
+	}
+}
+
+/* Spawn rcu_tasks_kthread() at first call to call_rcu_tasks(). */
+static void rcu_spawn_tasks_kthread(void)
+{
+	static DEFINE_MUTEX(rcu_tasks_kthread_mutex);
+	static struct task_struct *rcu_tasks_kthread_ptr;
+	struct task_struct *t;
+
+	if (ACCESS_ONCE(rcu_tasks_kthread_ptr)) {
+		smp_mb(); /* Ensure caller sees full kthread. */
+		return;
+	}
+	mutex_lock(&rcu_tasks_kthread_mutex);
+	if (rcu_tasks_kthread_ptr) {
+		mutex_unlock(&rcu_tasks_kthread_mutex);
+		return;
+	}
+	t = kthread_run(rcu_tasks_kthread, NULL, "rcu_tasks_kthread");
+	BUG_ON(IS_ERR(t));
+	smp_mb(); /* Ensure others see full kthread. */
+	ACCESS_ONCE(rcu_tasks_kthread_ptr) = t;
+	mutex_unlock(&rcu_tasks_kthread_mutex);
+}
+
+#endif /* #ifdef CONFIG_TASKS_RCU */
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 5918d227730f..348ec763b104 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -278,7 +278,7 @@ restart:
 		pending >>= softirq_bit;
 	}
 
-	rcu_bh_qs(smp_processor_id());
+	rcu_bh_qs();
 	local_irq_disable();
 
 	pending = local_softirq_pending();
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 75875a741b5e..ab456664609d 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1055,15 +1055,6 @@ static struct ctl_table kern_table[] = {
 		.child		= key_sysctls,
 	},
 #endif
-#ifdef CONFIG_RCU_TORTURE_TEST
-	{
-		.procname       = "rcutorture_runnable",
-		.data           = &rcutorture_runnable,
-		.maxlen         = sizeof(int),
-		.mode           = 0644,
-		.proc_handler	= proc_dointvec,
-	},
-#endif
 #ifdef CONFIG_PERF_EVENTS
 	/*
 	 * User-space scripts rely on the existence of this file
diff --git a/kernel/torture.c b/kernel/torture.c
index d600af21f022..dd70993c266c 100644
--- a/kernel/torture.c
+++ b/kernel/torture.c
@@ -211,18 +211,16 @@ EXPORT_SYMBOL_GPL(torture_onoff_cleanup);
 /*
  * Print online/offline testing statistics.
  */
-char *torture_onoff_stats(char *page)
+void torture_onoff_stats(void)
 {
 #ifdef CONFIG_HOTPLUG_CPU
-	page += sprintf(page,
-		       "onoff: %ld/%ld:%ld/%ld %d,%d:%d,%d %lu:%lu (HZ=%d) ",
-		       n_online_successes, n_online_attempts,
-		       n_offline_successes, n_offline_attempts,
-		       min_online, max_online,
-		       min_offline, max_offline,
-		       sum_online, sum_offline, HZ);
+	pr_cont("onoff: %ld/%ld:%ld/%ld %d,%d:%d,%d %lu:%lu (HZ=%d) ",
+		n_online_successes, n_online_attempts,
+		n_offline_successes, n_offline_attempts,
+		min_online, max_online,
+		min_offline, max_offline,
+		sum_online, sum_offline, HZ);
 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
-	return page;
 }
 EXPORT_SYMBOL_GPL(torture_onoff_stats);
 
@@ -635,8 +633,13 @@ EXPORT_SYMBOL_GPL(torture_init_end);
  *
  * This must be called before the caller starts shutting down its own
  * kthreads.
+ *
+ * Both torture_cleanup_begin() and torture_cleanup_end() must be paired,
+ * in order to correctly perform the cleanup. They are separated because
+ * threads can still need to reference the torture_type type, thus nullify
+ * only after completing all other relevant calls.
  */
-bool torture_cleanup(void)
+bool torture_cleanup_begin(void)
 {
 	mutex_lock(&fullstop_mutex);
 	if (ACCESS_ONCE(fullstop) == FULLSTOP_SHUTDOWN) {
@@ -651,12 +654,17 @@ bool torture_cleanup(void)
 	torture_shuffle_cleanup();
 	torture_stutter_cleanup();
 	torture_onoff_cleanup();
+	return false;
+}
+EXPORT_SYMBOL_GPL(torture_cleanup_begin);
+
+void torture_cleanup_end(void)
+{
 	mutex_lock(&fullstop_mutex);
 	torture_type = NULL;
 	mutex_unlock(&fullstop_mutex);
-	return false;
 }
-EXPORT_SYMBOL_GPL(torture_cleanup);
+EXPORT_SYMBOL_GPL(torture_cleanup_end);
 
 /*
  * Is it time for the current torture test to stop?