[3.13.y.z extended stable] Patch "mm/page-writeback.c: fix divide by zero in bdi_dirty_limits()" has been added to staging queue

[Kamal Mostafa]

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

    mm/page-writeback.c: fix divide by zero in bdi_dirty_limits()

to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11.6.

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

For more information about the 3.13.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From fbeb558dcf5f518b2a75949428cb1b88ebc92b69 Mon Sep 17 00:00:00 2001
From: Maxim Patlasov <MPatlasov at parallels.com>
Date: Wed, 30 Jul 2014 16:08:21 -0700
Subject: mm/page-writeback.c: fix divide by zero in bdi_dirty_limits()

commit f6789593d5cea42a4ecb1cbeab6a23ade5ebbba7 upstream.

Under memory pressure, it is possible for dirty_thresh, calculated by
global_dirty_limits() in balance_dirty_pages(), to equal zero.  Then, if
strictlimit is true, bdi_dirty_limits() tries to resolve the proportion:

  bdi_bg_thresh : bdi_thresh = background_thresh : dirty_thresh

by dividing by zero.

Signed-off-by: Maxim Patlasov <mpatlasov at parallels.com>
Acked-by: Rik van Riel <riel at redhat.com>
Cc: Michal Hocko <mhocko at suse.cz>
Cc: KOSAKI Motohiro <kosaki.motohiro at jp.fujitsu.com>
Cc: Wu Fengguang <fengguang.wu at intel.com>
Cc: Johannes Weiner <hannes at cmpxchg.org>
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/page-writeback.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index d013dba..9f45f87 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1324,9 +1324,9 @@ static inline void bdi_dirty_limits(struct backing_dev_info *bdi,
 	*bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);

 	if (bdi_bg_thresh)
-		*bdi_bg_thresh = div_u64((u64)*bdi_thresh *
-					 background_thresh,
-					 dirty_thresh);
+		*bdi_bg_thresh = dirty_thresh ? div_u64((u64)*bdi_thresh *
+							background_thresh,
+							dirty_thresh) : 0;

 	/*
 	 * In order to avoid the stacked BDI deadlock we need
--
1.9.1