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

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Message-ID: <f4a6ff9e-d631-42c4-a5e1-87e767771488@acm.org>
Date:   Thu, 9 Nov 2023 10:13:56 -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: [syzbot] [block?] WARNING in blk_mq_start_request

On 11/8/23 17:27, Chengming Zhou wrote:
> CONFIG_BLK_DEV_NULL_BLK_FAULT_INJECTION is enabled in the kernel config,
> so null_queue_rq() will return BLK_STS_RESOURCE or BLK_STS_DEV_RESOURCE
> for some requests, which have been marked as IN_FLIGHT status.
> 
> Then null_queue_rqs() put these requests in the rqlist and return back,
> blk-mq will try to queue them individually once again, caused the warning
> "WARN_ON_ONCE(blk_mq_rq_state(rq) != MQ_RQ_IDLE)" in blk_mq_start_request().
> 
> So handling of return value of null_queue_rq() in null_queue_rqs() is wrong,
> maybe we should __blk_mq_requeue_request() for these requests, before
> adding them in the rqlist?

Please follow the example of virtio_queue_rqs() and send any requests
that need to be requeued back to the block layer core instead of
handling these directly in null_queue_rqs().

Thanks,

Bart.