linux-kernel - Re: [syzbot] general protection fault in wb_timer

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Date:   Mon, 16 Aug 2021 11:33:36 +0200
From:   Christoph Hellwig <hch@....de>
To:     Hillf Danton <hdanton@...a.com>
Cc:     syzbot <syzbot+aa0801b6b32dca9dda82@...kaller.appspotmail.com>,
        axboe@...nel.dk, Christoph Hellwig <hch@....de>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] general protection fault in wb_timer_fn

On Mon, Aug 16, 2021 at 05:10:41PM +0800, Hillf Danton wrote:
> Remove and free all qos callbacks added, with cb->timer deleted in
> blk_stat_remove_callback().
> 
> only for thoughts.
> 
> +++ x/block/blk-sysfs.c
> @@ -800,9 +800,7 @@ static void blk_release_queue(struct kob
>  
>  	might_sleep();
>  
> -	if (test_bit(QUEUE_FLAG_POLL_STATS, &q->queue_flags))
> -		blk_stat_remove_callback(q, q->poll_cb);
> -	blk_stat_free_callback(q->poll_cb);
> +	rq_qos_exit(q);

rq_qos_exit is already called in blk_cleanup_queue, and the blk-mq
pollig doesn't even use the qos framework.  So I'm not sure what this
is supposed to help.