[3.19.y-ckt stable] Patch "dm cache: fix NULL pointer when switching from cleaner policy" 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 cache: fix NULL pointer when switching from cleaner policy

to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue

This patch is scheduled to be released in version 3.19.8-ckt10.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 2a3b137eb8406f2f0c34b9c39eecea51f0dc02a7 Mon Sep 17 00:00:00 2001
From: Joe Thornber <ejt at redhat.com>
Date: Fri, 9 Oct 2015 14:03:38 +0100
Subject: [PATCH 030/120] dm cache: fix NULL pointer when switching from
 cleaner policy

commit 2bffa1503c5c06192eb1459180fac4416575a966 upstream.

The cleaner policy doesn't make use of the per cache block hint space in
the metadata (unlike the other policies).  When switching from the
cleaner policy to mq or smq a NULL pointer crash (in dm_tm_new_block)
was observed.  The crash was caused by bugs in dm-cache-metadata.c
when trying to skip creation of the hint btree.

The minimal fix is to change hint size for the cleaner policy to 4 bytes
(only hint size supported).

Signed-off-by: Joe Thornber <ejt at redhat.com>
Signed-off-by: Mike Snitzer <snitzer at redhat.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/md/dm-cache-policy-cleaner.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/md/dm-cache-policy-cleaner.c b/drivers/md/dm-cache-policy-cleaner.c
index 004e463..8308f4b 100644
--- a/drivers/md/dm-cache-policy-cleaner.c
+++ b/drivers/md/dm-cache-policy-cleaner.c
@@ -435,7 +435,7 @@ static struct dm_cache_policy *wb_create(dm_cblock_t cache_size,
 static struct dm_cache_policy_type wb_policy_type = {
 	.name = "cleaner",
 	.version = {1, 0, 0},
-	.hint_size = 0,
+	.hint_size = 4,
 	.owner = THIS_MODULE,
 	.create = wb_create
 };
--
1.9.1