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dm cache: fix issue with background work locking

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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 trigger 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 has 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: b29d4986d0 ("dm cache: significant rework to leverage dm-bio-prison-v2")
Cc: stable@vger.kernel.org
Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>
Reviewed-by: Matthew Sakai <msakai@redhat.com>
Reviewed-by: Ming-Hung Tsai <mtsai@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
This commit is contained in:
Benjamin Marzinski 2026-08-25 15:22:26 -04:00 committed by Mikulas Patocka
parent 148845aa19
commit bc9781c024
1 changed files with 28 additions and 27 deletions
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55
drivers/md/dm-cache-target.c
View File

@ -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;