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

Pull v3.7 RCU commits from Paul E. McKenney:

"
0.	A fix for a latent bug that has been in RCU ever since the
        addition of CPU stall warnings.  This bug results in
        false-positive stall warnings, but thus far only on embedded
        systems with severely cut-down userspace configurations.
        This fix is located on an rcu/urgent branch, with the rest
        of the commits based on top of it.  This commit CCs stable.
        Given that the merge window is coming quite soon and given
        the small number of affected users, I do -not- recommend
        pushing it to 3.6, but the separate branch makes it easy to
        find if someone needs it.

1.	Further reductions in latency spikes for huge systems, along
        with additional boot-time adaptation to the actual hardware.
        This is a large change, as it moves RCU grace-period
        initialization and cleanup, along with quiescent-state forcing,
        from softirq to a kthread.  However, it appears to be in
        quite good shape (famous last words).  Posted to LKML at
        https://lkml.org/lkml/2012/9/20/427.
2.	Updates to documentation and rcutorture, the latter category
        including keeping statistics on CPU-hotplug latencies and
        fixing some initialization-time races.  Posted to LKML at
        https://lkml.org/lkml/2012/8/30/193.

3.	Miscellaneous fixes and improvements, posted to LKML at
        https://lkml.org/lkml/2012/8/30/199.

4.	CPU-hotplug fixes and improvements, posted to LKML at
        https://lkml.org/lkml/2012/8/30/292 for first three and at
        https://lkml.org/lkml/2012/8/3/416.

5.	Idle-loop fixes that were omitted on an earlier submission,
        posted to LKML at https://lkml.org/lkml/2012/8/30/251.
"

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

1 files changed, 166 insertions, 19 deletions

diff --git a/kernel/kthread.c b/kernel/kthread.c
index b579af57ea10..146a6fa96825 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -37,11 +37,20 @@ struct kthread_create_info
 };
 
 struct kthread {
-	int should_stop;
+	unsigned long flags;
+	unsigned int cpu;
 	void *data;
+	struct completion parked;
 	struct completion exited;
 };
 
+enum KTHREAD_BITS {
+	KTHREAD_IS_PER_CPU = 0,
+	KTHREAD_SHOULD_STOP,
+	KTHREAD_SHOULD_PARK,
+	KTHREAD_IS_PARKED,
+};
+
 #define to_kthread(tsk)	\
 	container_of((tsk)->vfork_done, struct kthread, exited)
 
@@ -52,13 +61,29 @@ struct kthread {
  * and this will return true.  You should then return, and your return
  * value will be passed through to kthread_stop().
  */
-int kthread_should_stop(void)
+bool kthread_should_stop(void)
 {
-	return to_kthread(current)->should_stop;
+	return test_bit(KTHREAD_SHOULD_STOP, &to_kthread(current)->flags);
 }
 EXPORT_SYMBOL(kthread_should_stop);
 
 /**
+ * kthread_should_park - should this kthread park now?
+ *
+ * When someone calls kthread_park() on your kthread, it will be woken
+ * and this will return true.  You should then do the necessary
+ * cleanup and call kthread_parkme()
+ *
+ * Similar to kthread_should_stop(), but this keeps the thread alive
+ * and in a park position. kthread_unpark() "restarts" the thread and
+ * calls the thread function again.
+ */
+bool kthread_should_park(void)
+{
+	return test_bit(KTHREAD_SHOULD_PARK, &to_kthread(current)->flags);
+}
+
+/**
  * kthread_freezable_should_stop - should this freezable kthread return now?
  * @was_frozen: optional out parameter, indicates whether %current was frozen
  *
@@ -96,6 +121,24 @@ void *kthread_data(struct task_struct *task)
 	return to_kthread(task)->data;
 }
 
+static void __kthread_parkme(struct kthread *self)
+{
+	__set_current_state(TASK_INTERRUPTIBLE);
+	while (test_bit(KTHREAD_SHOULD_PARK, &self->flags)) {
+		if (!test_and_set_bit(KTHREAD_IS_PARKED, &self->flags))
+			complete(&self->parked);
+		schedule();
+		__set_current_state(TASK_INTERRUPTIBLE);
+	}
+	clear_bit(KTHREAD_IS_PARKED, &self->flags);
+	__set_current_state(TASK_RUNNING);
+}
+
+void kthread_parkme(void)
+{
+	__kthread_parkme(to_kthread(current));
+}
+
 static int kthread(void *_create)
 {
 	/* Copy data: it's on kthread's stack */
@@ -105,9 +148,10 @@ static int kthread(void *_create)
 	struct kthread self;
 	int ret;
 
-	self.should_stop = 0;
+	self.flags = 0;
 	self.data = data;
 	init_completion(&self.exited);
+	init_completion(&self.parked);
 	current->vfork_done = &self.exited;
 
 	/* OK, tell user we're spawned, wait for stop or wakeup */
@@ -117,9 +161,11 @@ static int kthread(void *_create)
 	schedule();
 
 	ret = -EINTR;
-	if (!self.should_stop)
-		ret = threadfn(data);
 
+	if (!test_bit(KTHREAD_SHOULD_STOP, &self.flags)) {
+		__kthread_parkme(&self);
+		ret = threadfn(data);
+	}
 	/* we can't just return, we must preserve "self" on stack */
 	do_exit(ret);
 }
@@ -172,8 +218,7 @@ static void create_kthread(struct kthread_create_info *create)
  * Returns a task_struct or ERR_PTR(-ENOMEM).
  */
 struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
-					   void *data,
-					   int node,
+					   void *data, int node,
 					   const char namefmt[],
 					   ...)
 {
@@ -210,6 +255,13 @@ struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
 }
 EXPORT_SYMBOL(kthread_create_on_node);
 
+static void __kthread_bind(struct task_struct *p, unsigned int cpu)
+{
+	/* It's safe because the task is inactive. */
+	do_set_cpus_allowed(p, cpumask_of(cpu));
+	p->flags |= PF_THREAD_BOUND;
+}
+
 /**
  * kthread_bind - bind a just-created kthread to a cpu.
  * @p: thread created by kthread_create().
@@ -226,14 +278,112 @@ void kthread_bind(struct task_struct *p, unsigned int cpu)
 		WARN_ON(1);
 		return;
 	}
-
-	/* It's safe because the task is inactive. */
-	do_set_cpus_allowed(p, cpumask_of(cpu));
-	p->flags |= PF_THREAD_BOUND;
+	__kthread_bind(p, cpu);
 }
 EXPORT_SYMBOL(kthread_bind);
 
 /**
+ * kthread_create_on_cpu - Create a cpu bound kthread
+ * @threadfn: the function to run until signal_pending(current).
+ * @data: data ptr for @threadfn.
+ * @cpu: The cpu on which the thread should be bound,
+ * @namefmt: printf-style name for the thread. Format is restricted
+ *	     to "name.*%u". Code fills in cpu number.
+ *
+ * Description: This helper function creates and names a kernel thread
+ * The thread will be woken and put into park mode.
+ */
+struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data),
+					  void *data, unsigned int cpu,
+					  const char *namefmt)
+{
+	struct task_struct *p;
+
+	p = kthread_create_on_node(threadfn, data, cpu_to_node(cpu), namefmt,
+				   cpu);
+	if (IS_ERR(p))
+		return p;
+	set_bit(KTHREAD_IS_PER_CPU, &to_kthread(p)->flags);
+	to_kthread(p)->cpu = cpu;
+	/* Park the thread to get it out of TASK_UNINTERRUPTIBLE state */
+	kthread_park(p);
+	return p;
+}
+
+static struct kthread *task_get_live_kthread(struct task_struct *k)
+{
+	struct kthread *kthread;
+
+	get_task_struct(k);
+	kthread = to_kthread(k);
+	/* It might have exited */
+	barrier();
+	if (k->vfork_done != NULL)
+		return kthread;
+	return NULL;
+}
+
+/**
+ * kthread_unpark - unpark a thread created by kthread_create().
+ * @k:		thread created by kthread_create().
+ *
+ * Sets kthread_should_park() for @k to return false, wakes it, and
+ * waits for it to return. If the thread is marked percpu then its
+ * bound to the cpu again.
+ */
+void kthread_unpark(struct task_struct *k)
+{
+	struct kthread *kthread = task_get_live_kthread(k);
+
+	if (kthread) {
+		clear_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
+		/*
+		 * We clear the IS_PARKED bit here as we don't wait
+		 * until the task has left the park code. So if we'd
+		 * park before that happens we'd see the IS_PARKED bit
+		 * which might be about to be cleared.
+		 */
+		if (test_and_clear_bit(KTHREAD_IS_PARKED, &kthread->flags)) {
+			if (test_bit(KTHREAD_IS_PER_CPU, &kthread->flags))
+				__kthread_bind(k, kthread->cpu);
+			wake_up_process(k);
+		}
+	}
+	put_task_struct(k);
+}
+
+/**
+ * kthread_park - park a thread created by kthread_create().
+ * @k: thread created by kthread_create().
+ *
+ * Sets kthread_should_park() for @k to return true, wakes it, and
+ * waits for it to return. This can also be called after kthread_create()
+ * instead of calling wake_up_process(): the thread will park without
+ * calling threadfn().
+ *
+ * Returns 0 if the thread is parked, -ENOSYS if the thread exited.
+ * If called by the kthread itself just the park bit is set.
+ */
+int kthread_park(struct task_struct *k)
+{
+	struct kthread *kthread = task_get_live_kthread(k);
+	int ret = -ENOSYS;
+
+	if (kthread) {
+		if (!test_bit(KTHREAD_IS_PARKED, &kthread->flags)) {
+			set_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
+			if (k != current) {
+				wake_up_process(k);
+				wait_for_completion(&kthread->parked);
+			}
+		}
+		ret = 0;
+	}
+	put_task_struct(k);
+	return ret;
+}
+
+/**
  * kthread_stop - stop a thread created by kthread_create().
  * @k: thread created by kthread_create().
  *
@@ -250,16 +400,13 @@ EXPORT_SYMBOL(kthread_bind);
  */
 int kthread_stop(struct task_struct *k)
 {
-	struct kthread *kthread;
+	struct kthread *kthread = task_get_live_kthread(k);
 	int ret;
 
 	trace_sched_kthread_stop(k);
-	get_task_struct(k);
-
-	kthread = to_kthread(k);
-	barrier(); /* it might have exited */
-	if (k->vfork_done != NULL) {
-		kthread->should_stop = 1;
+	if (kthread) {
+		set_bit(KTHREAD_SHOULD_STOP, &kthread->flags);
+		clear_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
 		wake_up_process(k);
 		wait_for_completion(&kthread->exited);
 	}