[PATCH 3.12 008/104] mm/page-writeback.c: fix divide by zero in bdi_dirty_limits()

From: Jiri Slaby
Date: Wed Aug 20 2014 - 08:11:53 EST


From: Maxim Patlasov <MPatlasov@xxxxxxxxxxxxx>

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

===============

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@xxxxxxxxxxxxx>
Acked-by: Rik van Riel <riel@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxx>
Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Cc: Wu Fengguang <fengguang.wu@xxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
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 d013dba21429..9f45f87a5859 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
--
2.0.4

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