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[3.13,193/259] mm/page-writeback.c: fix divide by zero in bdi_dirty_limits()

Message ID 1407530482-4483-194-git-send-email-kamal@canonical.com
State New
Headers show

Commit Message

Kamal Mostafa Aug. 8, 2014, 8:40 p.m. UTC 
3.13.11.6 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Maxim Patlasov <MPatlasov@parallels.com>

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@parallels.com>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
 mm/page-writeback.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
diff mbox

Patch

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