mm, vmstat: fix wrong WQ sleep when memory reclaim doesn't make any progress

Jan Stancek has reported that system occasionally hanging after "oom01"
testcase from LTP triggers OOM.  Guessing from a result that there is a
kworker thread doing memory allocation and the values between "Node 0
Normal free:" and "Node 0 Normal:" differs when hanging, vmstat is not
up-to-date for some reason.

According to commit 373ccbe592 ("mm, vmstat: allow WQ concurrency to
discover memory reclaim doesn't make any progress"), it meant to force
the kworker thread to take a short sleep, but it by error used
schedule_timeout(1).  We missed that schedule_timeout() in state
TASK_RUNNING doesn't do anything.

Fix it by using schedule_timeout_uninterruptible(1) which forces the
kworker thread to take a short sleep in order to make sure that vmstat
is up-to-date.

Fixes: 373ccbe592 ("mm, vmstat: allow WQ concurrency to discover memory reclaim doesn't make any progress")
Signed-off-by: Tetsuo Handa <[email protected]>
Reported-by: Jan Stancek <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Cristopher Lameter <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Arkadiusz Miskiewicz <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/backing-dev.c

@@ -989,7 +989,7 @@ long wait_iff_congested(struct zone *zone, int sync, long timeout)
 		 * here rather than calling cond_resched().
 		 */
 		if (current->flags & PF_WQ_WORKER)
-			schedule_timeout(1);
+			schedule_timeout_uninterruptible(1);
 		else
 			cond_resched();