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>
diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index 42b5ca0..e6a9c06e 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -100,7 +100,7 @@
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 @@
/*
* 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 @@
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;