[3.13.y.z extended stable] Patch "dm bufio: fully initialize shrinker" has been added to staging queue

[Kamal Mostafa]

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

    dm bufio: fully initialize shrinker

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 b45bb0fda08b2fa736463782fd7ea258b568a396 Mon Sep 17 00:00:00 2001
From: Greg Thelen <gthelen at google.com>
Date: Thu, 31 Jul 2014 09:07:19 -0700
Subject: dm bufio: fully initialize shrinker

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 at google.com>
Acked-by: Mikulas Patocka <mpatocka at redhat.com>
Signed-off-by: Mike Snitzer <snitzer at redhat.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 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;
--
1.9.1