Commit 3e94d54e authored by Tian Lan's avatar Tian Lan Committed by Jens Axboe
Browse files

blk-mq: fix race condition in active queue accounting 



If multiple CPUs are sharing the same hardware queue, it can
cause leak in the active queue counter tracking when __blk_mq_tag_busy()
is executed simultaneously.

Fixes: ee78ec10 ("blk-mq: blk_mq_tag_busy is no need to return a value")
Signed-off-by: default avatarTian Lan <tian.lan@twosigma.com>
Reviewed-by: default avatarMing Lei <ming.lei@redhat.com>
Reviewed-by: default avatarDamien Le Moal <dlemoal@kernel.org>
Reviewed-by: default avatarJohn Garry <john.g.garry@oracle.com>
Link: https://lore.kernel.org/r/20230522210555.794134-1-tilan7663@gmail.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 8a2b20a9

block/blk-mq-tag.c

+8 −4
Original line number Diff line number Diff line
@@ -39,16 +39,20 @@ void __blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx) 
{

	unsigned int users;



	/*

	 * calling test_bit() prior to test_and_set_bit() is intentional,

	 * it avoids dirtying the cacheline if the queue is already active.

	 */

	if (blk_mq_is_shared_tags(hctx->flags)) {

		struct request_queue *q = hctx->queue;



		if (test_bit(QUEUE_FLAG_HCTX_ACTIVE, &q->queue_flags))

		if (test_bit(QUEUE_FLAG_HCTX_ACTIVE, &q->queue_flags) ||

		    test_and_set_bit(QUEUE_FLAG_HCTX_ACTIVE, &q->queue_flags))

			return;

		set_bit(QUEUE_FLAG_HCTX_ACTIVE, &q->queue_flags);

	} else {

		if (test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))

		if (test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state) ||

		    test_and_set_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))

			return;

		set_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state);

	}



	users = atomic_inc_return(&hctx->tags->active_queues);