Re: [PATCH v5 04/13] blk-rq-qos: fix possible debugfs_mutex deadlock

[Ming Lei <ming.lei@redhat.com>]

On Sun, Dec 14, 2025 at 06:13:59PM +0800, Yu Kuai wrote:
> Currently rq-qos debugfs entries are created from rq_qos_add(), while
> rq_qos_add() can be called while queue is still frozen. This can
> deadlock because creating new entries can trigger fs reclaim.
> 
> Fix this problem by delaying creating rq-qos debugfs entries after queue
> is unfrozen.
> 
> - For wbt, 1) it can be initialized by default, fix it by calling new
>   helper after wbt_init() from wbt_enable_default; 2) it can be
>   initialized by sysfs, fix it by calling new helper after queue is
>   unfrozen from queue_wb_lat_store().
> - For iocost and iolatency, they can only be initialized by blkcg
>   configuration, however, they don't have debugfs entries for now, hence
>   they are not handled yet.
> 
> Signed-off-by: Yu Kuai <yukuai@fnnas.com>

This patch need to rebase on the following -rc2.


Thanks,
Ming