[PATCH 05/14] hrtimer: Fix invalid wakeup in do_nanosleep

[Libin]

If thread is preempted before calling set_current_state(TASK_INTERRUPTIBLE),
and the other thread set the condition followed with wake_up_process. After
that when this thread is re-scheduled, calling set_current_state to set itself
as state TASK_INTERRUPTIBLE, if it is preempted again after that and before
__set_current_state(TASK_RUNNING), it triggers the invalid wakeup problem.

To solve this problem, using preempt_disable() to bound the operaion that
setting the task state and the conditions(set by the wake thread) validation.

Signed-off-by: Libin <huawei.libin@xxxxxxxxxx>
---
 kernel/hrtimer.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 383319b..a7845ba 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -1539,14 +1539,18 @@ static int __sched do_nanosleep(struct hrtimer_sleeper *t, enum hrtimer_mode mod
 {
 	hrtimer_init_sleeper(t, current);
 
+	preempt_disable();
 	do {
 		set_current_state(TASK_INTERRUPTIBLE);
 		hrtimer_start_expires(&t->timer, mode);
 		if (!hrtimer_active(&t->timer))
 			t->task = NULL;
 
-		if (likely(t->task))
+		if (likely(t->task)) {
+			preempt_enable();
 			freezable_schedule();
+			preempt_disable();
+		}
 
 		hrtimer_cancel(&t->timer);
 		mode = HRTIMER_MODE_ABS;
@@ -1554,6 +1558,7 @@ static int __sched do_nanosleep(struct hrtimer_sleeper *t, enum hrtimer_mode mod
 	} while (t->task && !signal_pending(current));
 
 	__set_current_state(TASK_RUNNING);
+	preempt_enable();
 
 	return t->task == NULL;
 }
-- 
1.8.2.1


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