block: disable the elevator int del_gendisk

The elevator is only used for file system requests, which are stopped in
del_gendisk.  Move disabling the elevator and freeing the scheduler tags
to the end of del_gendisk instead of doing that work in disk_release and
blk_cleanup_queue to avoid a use after free on q->tag_set from
disk_release as the tag_set might not be alive at that point.

Move the blk_qos_exit call as well, as it just depends on the elevator
exit and would be the only reason to keep the not exactly cheap queue
freeze in disk_release.

Fixes: e155b0c238b2 ("blk-mq: Use shared tags for shared sbitmap support")
Reported-by: syzbot+3e3f419f4a7816471838@syzkaller.appspotmail.com
Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: syzbot+3e3f419f4a7816471838@syzkaller.appspotmail.com
Link: https://lore.kernel.org/r/20220614074827.458955-2-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 0 insertions, 13 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index 06ff5bbfe8f6..27fb1357ad4b 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -322,19 +322,6 @@ void blk_cleanup_queue(struct request_queue *q)
 		blk_mq_exit_queue(q);
 	}
 
-	/*
-	 * In theory, request pool of sched_tags belongs to request queue.
-	 * However, the current implementation requires tag_set for freeing
-	 * requests, so free the pool now.
-	 *
-	 * Queue has become frozen, there can't be any in-queue requests, so
-	 * it is safe to free requests now.
-	 */
-	mutex_lock(&q->sysfs_lock);
-	if (q->elevator)
-		blk_mq_sched_free_rqs(q);
-	mutex_unlock(&q->sysfs_lock);
-
 	/* @q is and will stay empty, shutdown and put */
 	blk_put_queue(q);
 }