From mboxrd@z Thu Jan  1 00:00:00 1970
From: Sagi Grimberg <sagig@dev.mellanox.co.il>
Subject: Re: [RFC] Simlify dif_verify routines and fixup fileio protection
 information code.
Date: Thu, 16 Apr 2015 19:04:57 +0300
Message-ID: <552FDDA9.1050000@dev.mellanox.co.il>
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To: Akinobu Mita <akinobu.mita@gmail.com>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>, "Nicholas A. Bellinger" <nab@linux-iscsi.org>, target-devel@vger.kernel.org, "linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>, Christoph Hellwig <hch@lst.de>

On 4/16/2015 6:58 PM, Sagi Grimberg wrote:
> On 4/16/2015 4:46 PM, Akinobu Mita wrote:
>> 2015-04-16 17:52 GMT+09:00 Sagi Grimberg <sagig@dev.mellanox.co.il>:
>>> On 4/15/2015 7:10 PM, Martin K. Petersen wrote:
>>>>>>>>>
>>>>>>>>> "Sagi" == Sagi Grimberg <sagig@dev.mellanox.co.il> writes:
>>>>
>>>>
>>>>>>> By the commit 436f4a0a ("loopback: Add fabric_prot_type attribute
>>>>>>> support"), When WRITE_SAME command with WRPROTECT=0 is executed,
>>>>>>> sbc_dif_generate() is called but cmd->t_prot_sg is NULL as block
>>>>>>> layer didn't allocate it for WRITE_SAME.
>>>>
>>>>
>>>> Sagi> Actually this is a bug. Why didn't the initiator allocate
>>>> Sagi> integrity meta-data for WRITE_SAME? Looking at the code it looks
>>>> Sagi> like it should.
>>>>
>>>> We don't issue WRITE SAME with PI so there is no prot SGL.
>>>>
>>>
>>> Is there a specific reason why we don't?
>>
>> It is not only for the WRITE SAME requests from block device but
>> also for READ/WRITE with PROTECT=0 requests by SG_IO.
>>
>
> This is specific to loopback which is using target_submit_cmd_map_sgls()
> Other fabrics would allocate sgls per IO and the core would allocate
> protection SGLs as well.
>

By "This" I meant the NULL deref you are witnessing in for wrprotect=0.