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authorOmar Sandoval <osandov@fb.com>2018-02-27 16:56:43 -0800
committerJens Axboe <axboe@kernel.dk>2018-02-28 12:23:35 -0700
commit4ace53f1ed40a5cfee4bdd7614c8a8b2798227ad (patch)
treec766967b9ac9c5ae7a04035c0fa182fb27167d33 /lib/sbitmap.c
parente9a99a638800af25c7ed006c96fd1dabb99254b7 (diff)
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sbitmap: use test_and_set_bit_lock()/clear_bit_unlock()
sbitmap_queue_get()/sbitmap_queue_clear() are used for allocating/freeing a resource, so they should provide acquire/release barrier semantics, respectively. sbitmap_get() currently contains a full barrier, which is unnecessary, so use test_and_set_bit_lock() instead of test_and_set_bit() (these are equivalent on x86_64). sbitmap_clear_bit() does not imply any barriers, which is incorrect, as accesses of the resource (e.g., request) could potentially get reordered to after the clear_bit(). Introduce sbitmap_clear_bit_unlock() and use it for sbitmap_queue_clear() (this only adds a compiler barrier on x86_64). The other existing user of sbitmap_clear_bit() (the blk-mq software queue pending map) is serialized through a spinlock and does not need this. Reported-by: Tejun Heo <tj@kernel.org> Acked-by: Tejun Heo <tj@kernel.org> Signed-off-by: Omar Sandoval <osandov@fb.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'lib/sbitmap.c')
-rw-r--r--lib/sbitmap.c10
1 files changed, 5 insertions, 5 deletions
diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index 42b5ca0acf93..e6a9c06ec70c 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -100,7 +100,7 @@ static int __sbitmap_get_word(unsigned long *word, unsigned long depth,
return -1;
}
- if (!test_and_set_bit(nr, word))
+ if (!test_and_set_bit_lock(nr, word))
break;
hint = nr + 1;
@@ -434,9 +434,9 @@ static void sbq_wake_up(struct sbitmap_queue *sbq)
/*
* Pairs with the memory barrier in set_current_state() to ensure the
* proper ordering of clear_bit()/waitqueue_active() in the waker and
- * test_and_set_bit()/prepare_to_wait()/finish_wait() in the waiter. See
- * the comment on waitqueue_active(). This is __after_atomic because we
- * just did clear_bit() in the caller.
+ * test_and_set_bit_lock()/prepare_to_wait()/finish_wait() in the
+ * waiter. See the comment on waitqueue_active(). This is __after_atomic
+ * because we just did clear_bit_unlock() in the caller.
*/
smp_mb__after_atomic();
@@ -469,7 +469,7 @@ static void sbq_wake_up(struct sbitmap_queue *sbq)
void sbitmap_queue_clear(struct sbitmap_queue *sbq, unsigned int nr,
unsigned int cpu)
{
- sbitmap_clear_bit(&sbq->sb, nr);
+ sbitmap_clear_bit_unlock(&sbq->sb, nr);
sbq_wake_up(sbq);
if (likely(!sbq->round_robin && nr < sbq->sb.depth))
*per_cpu_ptr(sbq->alloc_hint, cpu) = nr;