worker_thread() can miss freeze_process()->signal_wake_up() if it happens
between try_to_freeze() and prepare_to_wait(). We should check freezing()
before entering schedule().
This race was introduced by me in
[PATCH 1/1] workqueue: don't migrate pending works from the dead CPU
Looks like mm/vmscan.c:kswapd() has the same race.
Signed-off-by: Oleg Nesterov <[email protected]>
--- 2.6.21-rc5-mm4/kernel/workqueue.c~wq_freeze 2007-04-07 20:11:14.000000000 +0400
+++ 2.6.21-rc5-mm4/kernel/workqueue.c 2007-04-08 21:37:43.000000000 +0400
@@ -307,14 +307,14 @@ static int worker_thread(void *__cwq)
do_sigaction(SIGCHLD, &sa, (struct k_sigaction *)0);
for (;;) {
- if (cwq->wq->freezeable)
- try_to_freeze();
-
prepare_to_wait(&cwq->more_work, &wait, TASK_INTERRUPTIBLE);
- if (!cwq->should_stop && list_empty(&cwq->worklist))
+ if (!freezing(current) && !cwq->should_stop
+ && list_empty(&cwq->worklist))
schedule();
finish_wait(&cwq->more_work, &wait);
+ try_to_freeze();
+
if (cwq_should_stop(cwq))
break;
-
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