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Subject: Re: BUG: scsi/qla2xxx: BUG_ON(blk_queued_rq(req) is triggered in
 blk_finish_request
To: qla2xxx-upstream@qlogic.com, himanshu.madhani@cavium.com,
        jthumshirn@suse.de
Cc: linux-scsi@vger.kernel.org,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "jejb@linux.vnet.ibm.com" <jejb@linux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        Junxiao Bi <junxiao.bi@oracle.com>
References: <5eb1eeaa-b148-7b90-eee4-e365ead49a5b@oracle.com>
From: "jianchao.wang" <jianchao.w.wang@oracle.com>
Message-ID: <8c7b011e-1379-c151-a187-94d8e0697fd9@oracle.com>
Date: Thu, 24 May 2018 09:50:35 +0800
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Would anyone please take a look at this ?

Thanks in advance
Jianchao

On 05/23/2018 11:55 AM, jianchao.wang wrote:
> 
> 
> Hi all
> 
> Our customer met a panic triggered by BUG_ON in blk_finish_request.
>>>From the dmesg log, the BUG_ON was triggered after command abort occurred many times.
> There is a race condition in the following scenario.
> 
> cpu A                                   cpu B
> kworker                                 interrupt
>                                                  
> scmd_eh_abort_handler()                               
>   -> scsi_try_to_abort_cmd()
>     -> qla2xxx_eh_abort()                        
>       -> qla2x00_eh_wait_on_command()   qla2x00_status_entry()   
>                                           -> qla2x00_sp_compl()
>                                             -> qla2x00_sp_free_dma()
>   -> scsi_queue_insert()                          
>     -> __scsi_queue_insert()                         
>       -> blk_requeue_request()
>         -> blk_clear_rq_complete()
>                                             -> scsi_done
>                                               -> blk_complete_request
>                                                 -> blk_mark_rq_complete       
>           -> elv_requeue_request()              -> __blk_complete_request()
>             -> __elv_add_request()
>             // req will be queued here                                                         
>                                                     BLK_SOFTIRQ
>                                                     scsi_softirq_done()
>                                                       -> scsi_finish_command()
>                                                         -> scsi_io_completion()
>                                                           -> scsi_end_request()
>                                                             -> blk_finish_request()  // BUG_ON(blk_queued_rq(req)) !!!
> 
> The issue will not be triggered most of time, because the request is marked as complete by timeout path.
> So the scsi_done from qla2x00_sp_compl does nothing.
> But as the scenario above, if the complete state has been cleaned by blk_requeue_request, we will get
> the request both requeued and completed, and then BUG_ON(blk_queued_rq(req)) in blk_finish_request comes up.
> 
> Is there any solution for this in qla2xxx driver side ?
> 
> Thanks
> Jianchao
> 
>