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Message-ID: <407be945-9fd2-8e00-e72b-82e2f311dbeb@huawei.com>
Date:   Sun, 24 Sep 2023 14:37:02 +0800
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Subject: Re: [PATCH 1/2] scsi: core: scsi_device_online() return false if
 state is SDEV_CANCEL
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To:     Bart Van Assche <bvanassche@acm.org>,
        "James E . J . Bottomley" <jejb@linux.ibm.com>,
        "Martin K . Petersen" <martin.petersen@oracle.com>
CC:     <linux-kernel@vger.kernel.org>, <louhongxiang@huawei.com>,
        <linux-scsi@vger.kernel.org>
References: <20230922093636.2645961-1-haowenchao2@huawei.com>
 <20230922093636.2645961-2-haowenchao2@huawei.com>
 <50b20a3e-e264-4788-8e52-f7b57cf944f0@acm.org>
From:   Wenchao Hao <haowenchao2@huawei.com>
In-Reply-To: <50b20a3e-e264-4788-8e52-f7b57cf944f0@acm.org>
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On 2023/9/22 23:23, Bart Van Assche wrote:
> On 9/22/23 02:36, Wenchao Hao wrote:
>> SDEV_CANCEL is set when removing device and scsi_device_online() should
>> return false if sdev_state is SDEV_CANCEL.
>>
>> IO hang would be caused if return true when state is SDEV_CANCEL with
>> following order:
>>
>> T1:                        T2:scsi_error_handler
>> __scsi_remove_device()
>>    scsi_device_set_state(sdev, SDEV_CANCEL)
>>                            scsi_eh_flush_done_q()
>>                         if (scsi_device_online(sdev))
>>                           scsi_queue_insert(scmd,...)
>>
>> The command added by scsi_queue_insert() would never be handled any
>> more.
> 
> Why not? I think the blk_mq_destroy_queue() call in __scsi_remove_device() will cause it to fail.
> 
> Thanks,
> 
> Bart.
> 

Sorry, I did not describe in detail, the __scsi_remove_device() would be blocked
in blk_mq_freeze_queue_wait() to wait all block requests finished, so
blk_mq_destroy_queue() would not be called, and the task which try to remove
scsi_device would be hung.