blk-mq: bitmap tag: fix races in bt_get() function (86fb5c56) · Commits · 戴 / test

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:

Alexander Gordeev <agordeev@redhat.com> Signed-off-by:

Jens Axboe <axboe@fb.com>

block/blk-mq-tag.c

+5 −8

Original line number	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);
		do {
		bool was_empty;

		was_empty = list_empty(&wait.task_list);
		prepare_to_wait(&bs->wait, &wait, TASK_UNINTERRUPTIBLE);

		tag = __bt_get(hctx, bt, last_tag);
		if (tag != -1)
		break;

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

		blk_mq_put_ctx(data->ctx);

		io_schedule();
		@@ -519,10 +513,13 @@ static int bt_alloc(struct blk_mq_bitmap_tags *bt, unsigned int depth,
		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);
		atomic_set(&bt->bs[i].wait_cnt, bt->wake_cnt);
		}

		bt_update_count(bt, depth);
		return 0;
		}

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