blk-mq: Allow blocking queue tag iter callbacks (530ca2c9) · Commits · 戴 / test

A recent commit runs tag iterator callbacks under the rcu read lock, but existing callbacks do not satisfy the non-blocking requirement. The commit intended to prevent an iterator from accessing a queue that's being modified. This patch fixes the original issue by taking a queue reference instead of reading it, which allows callbacks to make blocking calls. Fixes: ("blk-mq: sync the update nr_hw_queues with blk_mq_queue_tag_busy_iter") Acked-by:

Jianchao Wang <jianchao.w.wang@oracle.com> Signed-off-by:

Keith Busch <keith.busch@intel.com> Signed-off-by:

Jens Axboe <axboe@kernel.dk>

block/blk-mq-tag.c

+4 −9

Original line number	Diff line number	Diff line
		@@ -322,16 +322,11 @@ void blk_mq_queue_tag_busy_iter(struct request_queue q, busy_iter_fn fn,

		/*
		* __blk_mq_update_nr_hw_queues will update the nr_hw_queues and
		* queue_hw_ctx after freeze the queue. So we could use q_usage_counter
		* to avoid race with it. __blk_mq_update_nr_hw_queues will users
		* synchronize_rcu to ensure all of the users go out of the critical
		* section below and see zeroed q_usage_counter.
		* queue_hw_ctx after freeze the queue, so we use q_usage_counter
		* to avoid race with it.
		*/
		rcu_read_lock();
		if (percpu_ref_is_zero(&q->q_usage_counter)) {
		rcu_read_unlock();
		if (!percpu_ref_tryget(&q->q_usage_counter))
		return;
		}

		queue_for_each_hw_ctx(q, hctx, i) {
		struct blk_mq_tags *tags = hctx->tags;
		@@ -347,7 +342,7 @@ void blk_mq_queue_tag_busy_iter(struct request_queue q, busy_iter_fn fn,
		bt_for_each(hctx, &tags->breserved_tags, fn, priv, true);
		bt_for_each(hctx, &tags->bitmap_tags, fn, priv, false);
		}
		rcu_read_unlock();
		blk_queue_exit(q);
		}

		static int bt_alloc(struct sbitmap_queue *bt, unsigned int depth,

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