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Date: Fri, 2 May 2014 08:38:41 -0700
From: Kamal Mostafa <kamal@...onical.com>
To: linux-kernel@...r.kernel.org, stable@...r.kernel.org,
kernel-team@...ts.ubuntu.com
Cc: Joe Thornber <ejt@...hat.com>, Mike Snitzer <snitzer@...hat.com>,
Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 3.13 133/151] dm cache: fix a lock-inversion
3.13.11.1 -stable review patch. If anyone has any objections, please let me know.
------------------
From: Joe Thornber <ejt@...hat.com>
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@...hat.com>
Signed-off-by: Joe Thornber <ejt@...hat.com>
Signed-off-by: Mike Snitzer <snitzer@...hat.com>
[ kamal: backport to 3.13: omitted cache_target version string change ]
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
drivers/md/dm-cache-metadata.c | 35 +++++++++++++++++------------------
drivers/md/dm-cache-metadata.h | 9 +--------
drivers/md/dm-cache-target.c | 26 +-------------------------
3 files changed, 19 insertions(+), 51 deletions(-)
diff --git a/drivers/md/dm-cache-metadata.c b/drivers/md/dm-cache-metadata.c
index 53ab31e..5320332 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 cd906f1..f0fb1dd 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 0411e9f..0826650 100644
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -2589,30 +2589,6 @@ 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
*/
@@ -2630,7 +2606,7 @@ 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");
--
1.9.1
--
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