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Subject: Re: [PATCH] kyber: Fix crash in kyber_finish_request()
To:     Omar Sandoval <osandov@osandov.com>
Cc:     Yang Yang <yang.yang@vivo.com>, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, onlyfever@icloud.com
References: <20200907074346.5383-1-yang.yang@vivo.com>
 <8b714da7-97b2-f8d2-4be7-c192130c33af@kernel.dk>
 <20200908190009.GA142421@relinquished.localdomain>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <51e9345b-7c65-e35b-148f-bc9c5e1f7dcf@kernel.dk>
Date:   Tue, 8 Sep 2020 13:49:03 -0600
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On 9/8/20 1:00 PM, Omar Sandoval wrote:
> On Mon, Sep 07, 2020 at 10:41:16AM -0600, Jens Axboe wrote:
>> CC Omar
>>
>> On 9/7/20 1:43 AM, Yang Yang wrote:
>>> Kernel crash when requeue flush request.
>>> It can be reproduced as below:
>>>
>>> [    2.517297] Unable to handle kernel paging request at virtual address ffffffd8071c0b00
>>> ...
>>> [    2.517468] pc : clear_bit+0x18/0x2c
>>> [    2.517502] lr : sbitmap_queue_clear+0x40/0x228
>>> [    2.517503] sp : ffffff800832bc60 pstate : 00c00145
>>> ...
>>> [    2.517599] Process ksoftirqd/5 (pid: 51, stack limit = 0xffffff8008328000)
>>> [    2.517602] Call trace:
>>> [    2.517606]  clear_bit+0x18/0x2c
>>> [    2.517619]  kyber_finish_request+0x74/0x80
>>> [    2.517627]  blk_mq_requeue_request+0x3c/0xc0
>>> [    2.517637]  __scsi_queue_insert+0x11c/0x148
>>> [    2.517640]  scsi_softirq_done+0x114/0x130
>>> [    2.517643]  blk_done_softirq+0x7c/0xb0
>>> [    2.517651]  __do_softirq+0x208/0x3bc
>>> [    2.517657]  run_ksoftirqd+0x34/0x60
>>> [    2.517663]  smpboot_thread_fn+0x1c4/0x2c0
>>> [    2.517667]  kthread+0x110/0x120
>>> [    2.517669]  ret_from_fork+0x10/0x18
>>>
>>> Signed-off-by: Yang Yang <yang.yang@vivo.com>
>>> ---
>>>  block/kyber-iosched.c | 3 +++
>>>  1 file changed, 3 insertions(+)
>>>
>>> diff --git a/block/kyber-iosched.c b/block/kyber-iosched.c
>>> index a38c5ab103d1..af73afe7a05c 100644
>>> --- a/block/kyber-iosched.c
>>> +++ b/block/kyber-iosched.c
>>> @@ -611,6 +611,9 @@ static void kyber_finish_request(struct request *rq)
>>>  {
>>>  	struct kyber_queue_data *kqd = rq->q->elevator->elevator_data;
>>>  
>>> +	if (unlikely(!(rq->rq_flags & RQF_ELVPRIV)))
>>> +		return;
>>> +
>>>  	rq_clear_domain_token(kqd, rq);
>>>  }
>>>  
>>>
> 
> It looks like BFQ also has this check. Wouldn't it make more sense to
> check it in blk-mq, like we do for .finish_request() in
> blk_mq_free_request()? Something along these lines:

Yeah I think so, that's much better than working around it in the
consumer of it.

-- 
Jens Axboe