From 0596661f0a16d9d69bf1033320e70b6ff52b5e81 Mon Sep 17 00:00:00 2001 From: Joe Thornber Date: Thu, 3 Apr 2014 16:16:44 +0100 Subject: 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 Signed-off-by: Joe Thornber Signed-off-by: Mike Snitzer Cc: stable@vger.kernel.org --- drivers/md/dm-cache-metadata.c | 35 +++++++++++++++++------------------ 1 file changed, 17 insertions(+), 18 deletions(-) (limited to 'drivers/md/dm-cache-metadata.c') 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; -- cgit