[PATCH 3.19.y-ckt 066/196] mm, vmstat: fix wrong WQ sleep when memory reclaim doesn't make any progress

[Kamal Mostafa]

3.19.8-ckt16 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Tetsuo Handa <penguin-kernel at i-love.sakura.ne.jp>

commit 564e81a57f9788b1475127012e0fd44e9049e342 upstream.

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")
Signed-off-by: Tetsuo Handa <penguin-kernel at I-love.SAKURA.ne.jp>
Reported-by: Jan Stancek <jstancek at redhat.com>
Acked-by: Michal Hocko <mhocko at suse.com>
Cc: Tejun Heo <tj at kernel.org>
Cc: Cristopher Lameter <clameter at sgi.com>
Cc: Joonsoo Kim <iamjoonsoo.kim at lge.com>
Cc: Arkadiusz Miskiewicz <arekm at maven.pl>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 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 b685f4c..ace24de 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -635,7 +635,7 @@ 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();
 
-- 
2.7.0