block: properly protect the 'queue' kobj in blk_unregister_queue (667257e8) · Commits · 戴 / test

The original commit (block: fix warning when I/O elevator is changed as request_queue is being removed) is pretty conflated. "conflated" because the resource being protected by q->sysfs_lock isn't the queue_flags (it is the 'queue' kobj). q->sysfs_lock serializes __elevator_change() (via elv_iosched_store) from racing with blk_unregister_queue(): 1) By holding q->sysfs_lock first, __elevator_change() can complete before a racing blk_unregister_queue(). 2) Conversely, __elevator_change() is testing for QUEUE_FLAG_REGISTERED in case elv_iosched_store() loses the race with blk_unregister_queue(), it needs a way to know the 'queue' kobj isn't there. Expand the scope of blk_unregister_queue()'s q->sysfs_lock use so it is held until after the 'queue' kobj is removed. To do so blk_mq_unregister_dev() must not also take q->sysfs_lock. So rename __blk_mq_unregister_dev() to blk_mq_unregister_dev(). Also, blk_unregister_queue() should use q->queue_lock to protect against any concurrent writes to q->queue_flags -- even though chances are the queue is being cleaned up so no concurrent writes are likely. Fixes: ("block: fix warning when I/O elevator is changed as request_queue is being removed") Signed-off-by:

Mike Snitzer <snitzer@redhat.com> Reviewed-by:

Ming Lei <ming.lei@redhat.com> Signed-off-by:

Jens Axboe <axboe@kernel.dk>

block/blk-mq-sysfs.c

+1 −8

Original line number	Diff line number	Diff line
		@@ -248,7 +248,7 @@ static int blk_mq_register_hctx(struct blk_mq_hw_ctx *hctx)
		return ret;
		}

		static void __blk_mq_unregister_dev(struct device dev, struct request_queue q)
		void blk_mq_unregister_dev(struct device dev, struct request_queue q)
		{
		struct blk_mq_hw_ctx *hctx;
		int i;
		@@ -265,13 +265,6 @@ static void __blk_mq_unregister_dev(struct device dev, struct request_queue q)
		q->mq_sysfs_init_done = false;
		}

		void blk_mq_unregister_dev(struct device dev, struct request_queue q)
		{
		mutex_lock(&q->sysfs_lock);
		__blk_mq_unregister_dev(dev, q);
		mutex_unlock(&q->sysfs_lock);
		}

		void blk_mq_hctx_kobj_init(struct blk_mq_hw_ctx *hctx)
		{
		kobject_init(&hctx->kobj, &blk_mq_hw_ktype);

block/blk-sysfs.c

+10 −3

Original line number	Diff line number	Diff line
		@@ -929,12 +929,17 @@ void blk_unregister_queue(struct gendisk *disk)
		if (WARN_ON(!q))
		return;

		/*
		* Protect against the 'queue' kobj being accessed
		* while/after it is removed.
		*/
		mutex_lock(&q->sysfs_lock);
		queue_flag_clear_unlocked(QUEUE_FLAG_REGISTERED, q);
		mutex_unlock(&q->sysfs_lock);

		wbt_exit(q);
		spin_lock_irq(q->queue_lock);
		queue_flag_clear(QUEUE_FLAG_REGISTERED, q);
		spin_unlock_irq(q->queue_lock);

		wbt_exit(q);

		if (q->mq_ops)
		blk_mq_unregister_dev(disk_to_dev(disk), q);
		@@ -946,4 +951,6 @@ void blk_unregister_queue(struct gendisk *disk)
		kobject_del(&q->kobj);
		blk_trace_remove_sysfs(disk_to_dev(disk));
		kobject_put(&disk_to_dev(disk)->kobj);

		mutex_unlock(&q->sysfs_lock);
		}

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