Commit 0a67b5a9 authored Sep 12, 2019 by Ming Lei Committed by Jens Axboe Sep 12, 2019

block: fix race between switching elevator and removing queues



cecf5d87 ("block: split .sysfs_lock into two locks") starts to
release & actuire sysfs_lock again during switching elevator. So it
isn't enough to prevent switching elevator from happening by simply
clearing QUEUE_FLAG_REGISTERED with holding sysfs_lock, because
in-progress switch still can move on after re-acquiring the lock,
meantime the flag of QUEUE_FLAG_REGISTERED won't get checked.

Fixes this issue by checking 'q->elevator' directly & locklessly after
q->kobj is removed in blk_unregister_queue(), this way is safe because
q->elevator can't be changed at that time.

Fixes: cecf5d87 ("block: split .sysfs_lock into two locks")
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Mike Snitzer <snitzer@redhat.com>
Cc: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent b804049d

block/blk-sysfs.c

+5 −3

Original line number	Diff line number	Diff line
		@@ -1030,7 +1030,6 @@ EXPORT_SYMBOL_GPL(blk_register_queue);
		void blk_unregister_queue(struct gendisk *disk)
		{
		struct request_queue *q = disk->queue;
		bool has_elevator;

		if (WARN_ON(!q))
		return;
		@@ -1046,7 +1045,6 @@ void blk_unregister_queue(struct gendisk *disk)
		*/
		mutex_lock(&q->sysfs_lock);
		blk_queue_flag_clear(QUEUE_FLAG_REGISTERED, q);
		has_elevator = !!q->elevator;
		mutex_unlock(&q->sysfs_lock);

		mutex_lock(&q->sysfs_dir_lock);
		@@ -1061,7 +1059,11 @@ void blk_unregister_queue(struct gendisk *disk)
		kobject_del(&q->kobj);
		blk_trace_remove_sysfs(disk_to_dev(disk));

		if (has_elevator)
		/*
		* q->kobj has been removed, so it is safe to check if elevator
		* exists without holding q->sysfs_lock.
		*/
		if (q->elevator)
		elv_unregister_queue(q);
		mutex_unlock(&q->sysfs_dir_lock);