dm cache used a rw_semaphore for background_work_lock. Write locks on
rw_semaphores have strict owner semantics, but there was no guarantee
that the process that locked background_work_lock was the same process
that unlocked it. This can be easily seen using a kernel compiled with
CONFIG_DEBUG_RWSEMS. Given a dm cache device <cache>, run: 'dmsetup
suspend <cache> && dmsetup resume <cache>'. This will tigger a kernel
warning:
DEBUG_RWSEMS_WARN_ON((rwsem_owner(sem) != current) && !rwsem_test_oflags(sem,
RWSEM_NONSPINNABLE))
triggered by cache_resume(). To fix this, switch from a rw_semaphore to
a spinlock and a wait queue. dm cache already hasd a wait queue and
associated counter, migration_wait and nr_allocated_migrations, that was
getting woken up when background work was getting completed, but wasn't
actually used by anything. This is replaced by the background_work queue
and counter.
Fixes: b29d4986d0da ("dm cache: significant rework to leverage
dm-bio-prison-v2")
Signed-off-by: Benjamin Marzinski <[email protected]>
---
drivers/md/dm-cache-target.c | 55 ++++++++++++++++++------------------
1 file changed, 28 insertions(+), 27 deletions(-)
diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
index 33dbc71b730f..d8d9c63d2a67 100644
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -340,8 +340,6 @@ struct cache {
struct list_head invalidation_requests;
sector_t migration_threshold;
- wait_queue_head_t migration_wait;
- atomic_t nr_allocated_migrations;
/*
* The number of in flight migrations that are performing
@@ -397,7 +395,11 @@ struct cache {
bool loaded_mappings:1;
bool loaded_discards:1;
- struct rw_semaphore background_work_lock;
+ /* background work management */
+ bool background_work_allowed;
+ unsigned background_work_nr;
+ spinlock_t background_work_lock;
+ wait_queue_head_t background_work_wait;
struct batcher committer;
struct work_struct commit_ws;
@@ -488,19 +490,13 @@ static struct dm_cache_migration *alloc_migration(struct
cache *cache)
memset(mg, 0, sizeof(*mg));
mg->cache = cache;
- atomic_inc(&cache->nr_allocated_migrations);
return mg;
}
static void free_migration(struct dm_cache_migration *mg)
{
- struct cache *cache = mg->cache;
-
- if (atomic_dec_and_test(&cache->nr_allocated_migrations))
- wake_up(&cache->migration_wait);
-
- mempool_free(mg, &cache->migration_pool);
+ mempool_free(mg, &mg->cache->migration_pool);
}
/*----------------------------------------------------------------*/
@@ -1030,34 +1026,39 @@ static void calc_discard_block_range(struct cache
*cache, struct bio *bio,
static void prevent_background_work(struct cache *cache)
{
- lockdep_off();
- down_write(&cache->background_work_lock);
- lockdep_on();
+ spin_lock_irq(&cache->background_work_lock);
+ cache->background_work_allowed = false;
+ wait_event_lock_irq(cache->background_work_wait,
+ cache->background_work_nr == 0,
+ cache->background_work_lock);
+ spin_unlock_irq(&cache->background_work_lock);
}
static void allow_background_work(struct cache *cache)
{
- lockdep_off();
- up_write(&cache->background_work_lock);
- lockdep_on();
+ spin_lock_irq(&cache->background_work_lock);
+ cache->background_work_allowed = true;
+ spin_unlock_irq(&cache->background_work_lock);
}
static bool background_work_begin(struct cache *cache)
{
bool r;
- lockdep_off();
- r = down_read_trylock(&cache->background_work_lock);
- lockdep_on();
-
+ spin_lock_irq(&cache->background_work_lock);
+ r = cache->background_work_allowed;
+ if (r)
+ cache->background_work_nr++;
+ spin_unlock_irq(&cache->background_work_lock);
return r;
}
static void background_work_end(struct cache *cache)
{
- lockdep_off();
- up_read(&cache->background_work_lock);
- lockdep_on();
+ spin_lock_irq(&cache->background_work_lock);
+ if (--cache->background_work_nr == 0)
+ wake_up(&cache->background_work_wait);
+ spin_unlock_irq(&cache->background_work_lock);
}
/*----------------------------------------------------------------*/
@@ -2507,9 +2508,7 @@ static int cache_create(struct cache_args *ca, struct
cache **result)
spin_lock_init(&cache->lock);
bio_list_init(&cache->deferred_bios);
- atomic_set(&cache->nr_allocated_migrations, 0);
atomic_set(&cache->nr_io_migrations, 0);
- init_waitqueue_head(&cache->migration_wait);
r = -ENOMEM;
atomic_set(&cache->nr_dirty, 0);
@@ -2592,8 +2591,10 @@ static int cache_create(struct cache_args *ca, struct
cache **result)
issue_op, cache, cache->wq);
dm_iot_init(&cache->tracker);
- init_rwsem(&cache->background_work_lock);
- prevent_background_work(cache);
+ init_waitqueue_head(&cache->background_work_wait);
+ spin_lock_init(&cache->background_work_lock);
+ cache->background_work_allowed = false;
+ cache->background_work_nr = 0;
*result = cache;
return 0;
--
2.53.0
