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

[Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>]

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 373ccbe59270 ("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: 373ccbe59270 ("mm, vmstat: allow WQ concurrency to discover memory reclaim doesn't make any progress")
Reported-by: Jan Stancek <jstancek@redhat.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Cristopher Lameter <clameter@sgi.com>
Cc: Joonsoo Kim <js1304@gmail.com>
Cc: Arkadiusz Miskiewicz <arekm@maven.pl>
Cc: <stable@vger.kernel.org>
---
 mm/backing-dev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 7340353..cbe6f0b 100644
--- a/mm/backing-dev.c
+++ b/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();
 
-- 
1.8.3.1

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