[PATCH 04/14] exit: Fix invalid wakeup in do_wait

[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/exit.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index a949819..1ea7736 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1521,7 +1521,6 @@ repeat:
 	   (!wo->wo_pid || hlist_empty(&wo->wo_pid->tasks[wo->wo_type])))
 		goto notask;
 
-	set_current_state(TASK_INTERRUPTIBLE);
 	read_lock(&tasklist_lock);
 	tsk = current;
 	do {
@@ -1539,16 +1538,20 @@ repeat:
 	read_unlock(&tasklist_lock);
 
 notask:
+	preempt_disable();
+	set_current_state(TASK_INTERRUPTIBLE);
 	retval = wo->notask_error;
 	if (!retval && !(wo->wo_flags & WNOHANG)) {
 		retval = -ERESTARTSYS;
 		if (!signal_pending(current)) {
+			preempt_enable();
 			schedule();
 			goto repeat;
 		}
 	}
-end:
 	__set_current_state(TASK_RUNNING);
+	preempt_enable();
+end:
 	remove_wait_queue(&current->signal->wait_chldexit, &wo->child_wait);
 	return retval;
 }
-- 
1.8.2.1


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