dm cache: fix a lock-inversion
When suspending a cache the policy is walked and the individual policy
hints written to the metadata via sync_metadata(). This led to this
lock order:
policy->lock
cache_metadata->root_lock
When loading the cache target the policy is populated while the metadata
lock is held:
cache_metadata->root_lock
policy->lock
Fix this potential lock-inversion (ABBA) deadlock in sync_metadata() by
ensuring the cache_metadata root_lock is held whilst all the hints are
written, rather than being repeatedly locked while policy->lock is held
(as was the case with each callout that policy_walk_mappings() made to
the old save_hint() method).
Found by turning on the CONFIG_PROVE_LOCKING ("Lock debugging: prove
locking correctness") build option. However, it is not clear how the
LOCKDEP reported paths can lead to a deadlock since the two paths,
suspending a target and loading a target, never occur at the same time.
But that doesn't mean the same lock-inversion couldn't have occurred
elsewhere.
Reported-by: Marian Csontos <mcsontos@redhat.com>
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-target.c b/drivers/md/dm-cache-target.c
index 8534679..1bf4a71 100644
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -2582,30 +2582,6 @@
return 0;
}
-static int save_hint(void *context, dm_cblock_t cblock, dm_oblock_t oblock,
- uint32_t hint)
-{
- struct cache *cache = context;
- return dm_cache_save_hint(cache->cmd, cblock, hint);
-}
-
-static int write_hints(struct cache *cache)
-{
- int r;
-
- r = dm_cache_begin_hints(cache->cmd, cache->policy);
- if (r) {
- DMERR("dm_cache_begin_hints failed");
- return r;
- }
-
- r = policy_walk_mappings(cache->policy, save_hint, cache);
- if (r)
- DMERR("policy_walk_mappings failed");
-
- return r;
-}
-
/*
* returns true on success
*/
@@ -2623,7 +2599,7 @@
save_stats(cache);
- r3 = write_hints(cache);
+ r3 = dm_cache_write_hints(cache->cmd, cache->policy);
if (r3)
DMERR("could not write hints");
@@ -3094,7 +3070,7 @@
static struct target_type cache_target = {
.name = "cache",
- .version = {1, 3, 0},
+ .version = {1, 4, 0},
.module = THIS_MODULE,
.ctr = cache_ctr,
.dtr = cache_dtr,