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authorJoe Thornber <ejt@redhat.com>2014-04-03 16:16:44 +0100
committerMike Snitzer <snitzer@redhat.com>2014-04-04 14:53:05 -0400
commit0596661f0a16d9d69bf1033320e70b6ff52b5e81 (patch)
tree5f2393ddece9f82f9fa7853c7aa6f9d9dbffddd1 /drivers
parent67324ea18812bc952ef96892fbd5817b9050413f (diff)
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
Diffstat (limited to 'drivers')
-rw-r--r--drivers/md/dm-cache-metadata.c35
-rw-r--r--drivers/md/dm-cache-metadata.h9
-rw-r--r--drivers/md/dm-cache-target.c28
3 files changed, 20 insertions, 52 deletions
diff --git a/drivers/md/dm-cache-metadata.c b/drivers/md/dm-cache-metadata.c
index 66f102ab102c..4ead4ba60656 100644
--- a/drivers/md/dm-cache-metadata.c
+++ b/drivers/md/dm-cache-metadata.c
@@ -1245,22 +1245,12 @@ static int begin_hints(struct dm_cache_metadata *cmd, struct dm_cache_policy *po
return 0;
}
-int dm_cache_begin_hints(struct dm_cache_metadata *cmd, struct dm_cache_policy *policy)
+static int save_hint(void *context, dm_cblock_t cblock, dm_oblock_t oblock, uint32_t hint)
{
+ struct dm_cache_metadata *cmd = context;
+ __le32 value = cpu_to_le32(hint);
int r;
- down_write(&cmd->root_lock);
- r = begin_hints(cmd, policy);
- up_write(&cmd->root_lock);
-
- return r;
-}
-
-static int save_hint(struct dm_cache_metadata *cmd, dm_cblock_t cblock,
- uint32_t hint)
-{
- int r;
- __le32 value = cpu_to_le32(hint);
__dm_bless_for_disk(&value);
r = dm_array_set_value(&cmd->hint_info, cmd->hint_root,
@@ -1270,16 +1260,25 @@ static int save_hint(struct dm_cache_metadata *cmd, dm_cblock_t cblock,
return r;
}
-int dm_cache_save_hint(struct dm_cache_metadata *cmd, dm_cblock_t cblock,
- uint32_t hint)
+static int write_hints(struct dm_cache_metadata *cmd, struct dm_cache_policy *policy)
{
int r;
- if (!hints_array_initialized(cmd))
- return 0;
+ r = begin_hints(cmd, policy);
+ if (r) {
+ DMERR("begin_hints failed");
+ return r;
+ }
+
+ return policy_walk_mappings(policy, save_hint, cmd);
+}
+
+int dm_cache_write_hints(struct dm_cache_metadata *cmd, struct dm_cache_policy *policy)
+{
+ int r;
down_write(&cmd->root_lock);
- r = save_hint(cmd, cblock, hint);
+ r = write_hints(cmd, policy);
up_write(&cmd->root_lock);
return r;
diff --git a/drivers/md/dm-cache-metadata.h b/drivers/md/dm-cache-metadata.h
index ce8468bb616e..cd70a78623a3 100644
--- a/drivers/md/dm-cache-metadata.h
+++ b/drivers/md/dm-cache-metadata.h
@@ -128,14 +128,7 @@ void dm_cache_dump(struct dm_cache_metadata *cmd);
* rather than querying the policy for each cblock, we let it walk its data
* structures and fill in the hints in whatever order it wishes.
*/
-
-int dm_cache_begin_hints(struct dm_cache_metadata *cmd, struct dm_cache_policy *p);
-
-/*
- * requests hints for every cblock and stores in the metadata device.
- */
-int dm_cache_save_hint(struct dm_cache_metadata *cmd,
- dm_cblock_t cblock, uint32_t hint);
+int dm_cache_write_hints(struct dm_cache_metadata *cmd, struct dm_cache_policy *p);
/*
* Query method. Are all the blocks in the cache clean?
diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
index 8534679918f4..1bf4a71919ec 100644
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -2582,30 +2582,6 @@ static int write_discard_bitset(struct cache *cache)
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 @@ static bool sync_metadata(struct cache *cache)
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 void cache_io_hints(struct dm_target *ti, struct queue_limits *limits)
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,