linux-kernel - [PATCH 3.12 015/104] dm bufio: fully initialize shrinker

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Message-Id: <9ee4fa038c195fc4ccd45aedaafbc8fd489ec33b.1408535000.git.jslaby@suse.cz>
Date:	Wed, 20 Aug 2014 13:42:38 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Greg Thelen <gthelen@...gle.com>,
	Mike Snitzer <snitzer@...hat.com>, Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 015/104] dm bufio: fully initialize shrinker

From: Greg Thelen <gthelen@...gle.com>

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

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

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@...gle.com>
Acked-by: Mikulas Patocka <mpatocka@...hat.com>
Signed-off-by: Mike Snitzer <snitzer@...hat.com>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 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 54bdd923316f..5056c45be97f 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;
-- 
2.0.4

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