[PATCH 10/14] time: Fix invalid wakeup in alarmtimer_do_nsleep

[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/time/alarmtimer.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/time/alarmtimer.c b/kernel/time/alarmtimer.c
index eec50fc..624f2ed 100644
--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -629,16 +629,21 @@ static enum alarmtimer_restart alarmtimer_nsleep_wakeup(struct alarm *alarm,
 static int alarmtimer_do_nsleep(struct alarm *alarm, ktime_t absexp)
 {
 	alarm->data = (void *)current;
+	preempt_disable();
 	do {
 		set_current_state(TASK_INTERRUPTIBLE);
 		alarm_start(alarm, absexp);
-		if (likely(alarm->data))
+		if (likely(alarm->data)) {
+			preempt_enable();
 			schedule();
+			preempt_disable();
+		}
 
 		alarm_cancel(alarm);
 	} while (alarm->data && !signal_pending(current));
 
 	__set_current_state(TASK_RUNNING);
+	preempt_enable();
 
 	return (alarm->data == NULL);
 }
-- 
1.8.2.1


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