Commit 86fb5c56 authored by Alexander Gordeev's avatar Alexander Gordeev Committed by Jens Axboe
Browse files

blk-mq: bitmap tag: fix races in bt_get() function 



This update fixes few issues in bt_get() function:

- list_empty(&wait.task_list) check is not protected;

- was_empty check is always true which results in *every* thread
  entering the loop resets bt_wait_state::wait_cnt counter rather
  than every bt->wake_cnt'th thread;

- 'bt_wait_state::wait_cnt' counter update is redundant, since
  it also gets reset in bt_clear_tag() function;

Cc: Christoph Hellwig <hch@infradead.org>
Cc: Ming Lei <tom.leiming@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: default avatarAlexander Gordeev <agordeev@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
parent 2971c35f

block/blk-mq-tag.c

+5 −8
Original line number Original line Diff line number Diff line
@@ -248,18 +248,12 @@ static int bt_get(struct blk_mq_alloc_data *data, 




	bs = bt_wait_ptr(bt, hctx);

	bs = bt_wait_ptr(bt, hctx);

	do {

	do {

		bool was_empty;



		was_empty = list_empty(&wait.task_list);

		prepare_to_wait(&bs->wait, &wait, TASK_UNINTERRUPTIBLE);

		prepare_to_wait(&bs->wait, &wait, TASK_UNINTERRUPTIBLE);





		tag = __bt_get(hctx, bt, last_tag);

		tag = __bt_get(hctx, bt, last_tag);

		if (tag != -1)

		if (tag != -1)

			break;

			break;





		if (was_empty)

			atomic_set(&bs->wait_cnt, bt->wake_cnt);



		blk_mq_put_ctx(data->ctx);

		blk_mq_put_ctx(data->ctx);





		io_schedule();

		io_schedule();
@@ -519,10 +513,13 @@ static int bt_alloc(struct blk_mq_bitmap_tags *bt, unsigned int depth, 
		return -ENOMEM;

		return -ENOMEM;

	}

	}





	for (i = 0; i < BT_WAIT_QUEUES; i++)

	bt_update_count(bt, depth);



	for (i = 0; i < BT_WAIT_QUEUES; i++) {

		init_waitqueue_head(&bt->bs[i].wait);

		init_waitqueue_head(&bt->bs[i].wait);

		atomic_set(&bt->bs[i].wait_cnt, bt->wake_cnt);

	}





	bt_update_count(bt, depth);

	return 0;

	return 0;

}

}