linux-kernel - Re: [External] Re: [syzbot] [block?] WARNING in blk_mq_start

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Message-ID: <3f2c2d33-2e5d-4c7b-80ea-e76885981dfb@acm.org>
Date:   Mon, 13 Nov 2023 15:57:38 -0800
From:   Bart Van Assche <bvanassche@....org>
To:     Chengming Zhou <zhouchengming@...edance.com>,
        syzbot <syzbot+fcc47ba2476570cbbeb0@...kaller.appspotmail.com>,
        axboe@...nel.dk, chaitanyak@...dia.com, eadavis@...com,
        hch@...radead.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, ming.lei@...hat.com,
        syzkaller-bugs@...glegroups.com
Subject: Re: [External] Re: [syzbot] [block?] WARNING in blk_mq_start_request

On 11/13/23 07:05, Chengming Zhou wrote:
> Ok, I reviewed the code of virtio_queue_rqs(), found the main difference
> is that request won't fail after blk_mq_start_request().
> 
> But in null_blk case, the request will fail after blk_mq_start_request(),
> return BLK_STS_RESOURCE or BLK_STS_DEV_RESOURCE. If we return these rqs
> back to the block layer core, they will be queued individually once again.
> So caused the warning.

I think it is safe to move the blk_mq_start_request() call under the if-block
that decides whether or not to requeue a request in null_queue_rq()

Thanks,

Bart.