worker_thread: fix racy try_to_freeze() usage

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 <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 4 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 87693b37d017..63885abf1ba0 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -308,14 +308,14 @@ 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;