diff options
author | Joe Thornber <ejt@redhat.com> | 2014-04-03 16:16:44 +0100 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2014-05-13 13:32:55 +0200 |
commit | 834c39f49d48a4ffb1d03d7348ae77e538db00a3 (patch) | |
tree | 11b9d840f42a597fcb3a910ba9d889feb7f186ef | |
parent | bd702549e01ac3eb04e9f5a6ec74050c5ada7087 (diff) | |
download | lwn-834c39f49d48a4ffb1d03d7348ae77e538db00a3.tar.gz lwn-834c39f49d48a4ffb1d03d7348ae77e538db00a3.zip |
dm cache: fix a lock-inversion
commit 0596661f0a16d9d69bf1033320e70b6ff52b5e81 upstream.
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r-- | drivers/md/dm-cache-metadata.c | 35 | ||||
-rw-r--r-- | drivers/md/dm-cache-metadata.h | 9 | ||||
-rw-r--r-- | drivers/md/dm-cache-target.c | 28 |
3 files changed, 20 insertions, 52 deletions
diff --git a/drivers/md/dm-cache-metadata.c b/drivers/md/dm-cache-metadata.c index 53ab31e4da57..5320332390b7 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 cd906f14f98d..f0fb1dd26524 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 bccb7ae34e61..b82b58f0bb85 100644 --- a/drivers/md/dm-cache-target.c +++ b/drivers/md/dm-cache-target.c @@ -2600,30 +2600,6 @@ 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 */ @@ -2641,7 +2617,7 @@ 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"); @@ -3114,7 +3090,7 @@ 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, |