[PATCH 4.2 248/258] dm cache: fix NULL pointer when switching from cleaner policy

[Greg Kroah-Hartman]

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

------------------

From: Joe Thornber <ejt@xxxxxxxxxx>

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@xxxxxxxxxx>
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/md/dm-cache-policy-cleaner.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/md/dm-cache-policy-cleaner.c
+++ b/drivers/md/dm-cache-policy-cleaner.c
@@ -436,7 +436,7 @@ static struct dm_cache_policy *wb_create
 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
 };


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