dm cache: fix NULL pointer when switching from cleaner policy

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@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org

diff --git a/drivers/md/dm-cache-policy-cleaner.c b/drivers/md/dm-cache-policy-cleaner.c
index 240c9f0e85e74e864624f0cb972c5b4394eaf11f..8a096456579bead67b182f27e65956341a7c8d73 100644 (file)
--- 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(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
 };