[PATCH 3.13 200/259] dm bufio: fully initialize shrinker

From: Kamal Mostafa
Date: Fri Aug 08 2014 - 17:08:18 EST -stable review patch. If anyone has any objections, please let me know.


From: Greg Thelen <gthelen@xxxxxxxxxx>

commit d8c712ea471ce7a4fd1734ad2211adf8469ddddc upstream.

1d3d4437eae1 ("vmscan: per-node deferred work") added a flags field to
struct shrinker assuming that all shrinkers were zero filled. The dm
bufio shrinker is not zero filled, which leaves arbitrary kmalloc() data
in flags. So far the only defined flags bit is SHRINKER_NUMA_AWARE.
But there are proposed patches which add other bits to shrinker.flags
(e.g. memcg awareness).

Rather than simply initializing the shrinker, this patch uses kzalloc()
when allocating the dm_bufio_client to ensure that the embedded shrinker
and any other similar structures are zeroed.

This fixes theoretical over aggressive shrinking of dm bufio objects.
If the uninitialized dm_bufio_client.shrinker.flags contains
SHRINKER_NUMA_AWARE then shrink_slab() would call the dm shrinker for
each numa node rather than just once. This has been broken since 3.12.

Signed-off-by: Greg Thelen <gthelen@xxxxxxxxxx>
Acked-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
drivers/md/dm-bufio.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
index 54bdd923..5056c45 100644
--- a/drivers/md/dm-bufio.c
+++ b/drivers/md/dm-bufio.c
@@ -1511,7 +1511,7 @@ struct dm_bufio_client *dm_bufio_client_create(struct block_device *bdev, unsign
BUG_ON(block_size < 1 << SECTOR_SHIFT ||
(block_size & (block_size - 1)));

- c = kmalloc(sizeof(*c), GFP_KERNEL);
+ c = kzalloc(sizeof(*c), GFP_KERNEL);
if (!c) {
r = -ENOMEM;
goto bad_client;

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