On 9/11/19 10:02 PM, Ming Lei wrote:
> cecf5d87ff20 ("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.
Thanks Ming, looks good to me and cleaner than before too.
--
Jens Axboe
