block: move removing elevator after deleting disk->queue_kobj

When blk_unregister_queue() is called from add_disk() failure path,
there is race in registering/unregistering elevator queue kobject
from the two code paths, because commit 559dc11143eb ("block: move
elv_register[unregister]_queue out of elevator_lock") moves elevator
queue register/unregister out of elevator lock.

Fix the race by removing elevator after deleting disk->queue_kobj,
because kobject_del(&disk->queue_kobj) drains in-progress sysfs
show()/store() of all attributes.

Fixes: 559dc11143eb ("block: move elv_register[unregister]_queue out of elevator_lock")
Reported-by: Nilay Shroff <nilay@linux.ibm.com>
Suggested-by: Nilay Shroff <nilay@linux.ibm.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
Link: https://lore.kernel.org/r/20250508085807.3175112-3-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 8be2390c3c195754fac8cdaeb0e16b2d5732eb5b..b2b9b89d6967ca9675a1648a6f0a3a253c1c2b5d 100644 (file)
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -948,9 +948,6 @@ void blk_unregister_queue(struct gendisk *disk)
                blk_mq_sysfs_unregister(disk);
        blk_crypto_sysfs_unregister(disk);
 
-       if (queue_is_mq(q))
-               elevator_set_none(q);
-
        mutex_lock(&q->sysfs_lock);
        disk_unregister_independent_access_ranges(disk);
        mutex_unlock(&q->sysfs_lock);
@@ -959,5 +956,8 @@ void blk_unregister_queue(struct gendisk *disk)
        kobject_uevent(&disk->queue_kobj, KOBJ_REMOVE);
        kobject_del(&disk->queue_kobj);
 
+       if (queue_is_mq(q))
+               elevator_set_none(q);
+
        blk_debugfs_remove(disk);
 }