From: Douglas Gilbert <dgilbert@interlog.com>
To: Tony Battersby <tonyb@cybernetics.com>,
linux-scsi@vger.kernel.org,
"James E.J. Bottomley" <JBottomley@parallels.com>,
Jens Axboe <axboe@kernel.dk>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH][SCSI] scsi-mq: fix requests that use a separate CDB buffer
Date: Fri, 22 Aug 2014 21:23:17 -0400 [thread overview]
Message-ID: <53F7ED05.1020400@interlog.com> (raw)
In-Reply-To: <53F7E5DF.3090809@interlog.com>
On 14-08-22 08:52 PM, Douglas Gilbert wrote:
> On 14-08-22 03:53 PM, Tony Battersby wrote:
>> This patch fixes code such as the following with scsi-mq enabled:
>>
>> rq = blk_get_request(...);
>> blk_rq_set_block_pc(rq);
>>
>> rq->cmd = my_cmd_buffer; /* separate CDB buffer */
>>
>> blk_execute_rq_nowait(...);
>>
>> Code like this appears in e.g. sg_start_req() in drivers/scsi/sg.c (for
>> large CDBs only). Without this patch, scsi_mq_prep_fn() will set
>> rq->cmd back to rq->__cmd, causing the wrong CDB to be sent to the device.
>
> Still looking at this one. 'sg_write_same --32' is my
> tool of choice. The target is scsi_debug which needs
> dif=2 (because mkp read the draft and only allows
> WRITE SAME(32) when the protection_level=2). Turned
> on command tracing and this is what I saw:
>
> sd 7:0:0:0: scsi_debug: cmd 9e 10 00 00 00 00 00 00 00 00 00 00 00 20 00 00
> sd 7:0:0:0: scsi_debug: cmd 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 08
> 24 6b d3 00 88 ff ff 20 00 c7 e8 00 00 00 00
>
> So the WS(32) command did get through, it is the second
> command that arrived on its tail that is a worry. So yes,
> IMO it is broken.
Got that wrong, that is a READ CAPACITY(16) that got
through properly (issued by sg_write_same) followed
by a 32 byte command of random bytes instead of the
requested WS(32), the first 6 bytes of which will
cause it to be parsed as a TEST UNIT READY.
> Now the >16 byte cdb length in the sg driver
> introduced in lk 3.17-rc1 was copied directly
> from the bsg driver which has had that capability
> for some time. Since your patch touches two files
> in drivers/block I'm wondering the bsg driver's
> >16 byte cdb length capability is broken in
> lk 3.16 ?
>
> Doug Gilbert
>
>
>
> --
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>
next prev parent reply other threads:[~2014-08-23 1:23 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-08-22 19:53 [PATCH][SCSI] scsi-mq: fix requests that use a separate CDB buffer Tony Battersby
2014-08-23 0:52 ` Douglas Gilbert
2014-08-23 1:23 ` Douglas Gilbert [this message]
2014-08-23 19:09 ` Douglas Gilbert
2014-08-25 14:04 ` Tony Battersby
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