[4.2.y-ckt stable] Patch "mm, vmstat: fix wrong WQ sleep when memory reclaim doesn't make any progress" has been added to the 4.2.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

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

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt5.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

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

>From c362ac701d20a408f9e3a7d5abae07c2dc356ea7 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel at i-love.sakura.ne.jp>
Date: Fri, 5 Feb 2016 15:36:30 -0800
Subject: mm, vmstat: fix wrong WQ sleep when memory reclaim doesn't make any
 progress

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 632b79b..ebab43e 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -975,7 +975,7 @@ 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