linux-kernel - Re: [PATCH RESEND 3/5] blk-iocost: fix incorrect lock order for rq_qos

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Message-ID: <d653c3c3-4b81-4af5-a05b-f95e972a0f01@linux.ibm.com>
Date: Mon, 17 Nov 2025 15:41:38 +0530
From: Nilay Shroff <nilay@...ux.ibm.com>
To: Yu Kuai <yukuai@...as.com>, axboe@...nel.dk, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, tj@...nel.org, ming.lei@...hat.com
Subject: Re: [PATCH RESEND 3/5] blk-iocost: fix incorrect lock order for
 rq_qos_mutex and freeze queue



On 11/16/25 9:40 AM, Yu Kuai wrote:
> Like wbt, rq_qos_add() can be called from two path and the lock order
> are inversely:
> 
> - From ioc_qos_write(), queue is already freezed before rq_qos_add();
> - From ioc_cost_model_write(), rq_qos_add() is called directly;
> 
> Fix this problem by converting to use blkg_conf_open_bdev_frozen()
> from ioc_cost_model_write(), then since all rq_qos_add() callers
> already freeze queue, convert to use rq_qos_add_freezed.
> 
> Signed-off-by: Yu Kuai <yukuai@...as.com>

Looks good to me:
Reviewed-by: Nilay Shroff <nilay@...ux.ibm.com>