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Subject[PATCH 10/14] time: Fix invalid wakeup in alarmtimer_do_nsleep
Date
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@huawei.com>
---
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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