linux-kernel - Re: New 2.6.24.2 SG

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Date:	Wed, 05 Mar 2008 11:28:42 -0500
From:	Mark Hounschell <markh@...pro.net>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
CC:	Mark Hounschell <dmarkh@....rr.com>,
	Mike Christie <michaelc@...wisc.edu>,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
	Tony Battersby <tonyb@...ernetics.com>
Subject: Re: New 2.6.24.2 SG_IO SCSI problems

James Bottomley wrote:
> On Wed, 2008-03-05 at 06:58 -0500, Mark Hounschell wrote:
>> Mike Christie wrote:
>>> Mark Hounschell wrote:
>>>> Mark Hounschell wrote:
>>>>> Mike Christie wrote:
>>>>>> Mike Christie wrote:
>>>>>>> Mark Hounschell wrote:
>>>>>>>> I seem to have run into some sort of regression in the SG_IO
>>>>>>>> interface of 2.6.24.2. I have an application that up until 2.6.24
>>>>>>>> worked fine. The 2.6.23.16 kernel works fine.
>>>>>>>>
>>>>>>>> During reads I get these kernel messages. Writes and other functions
>>>>>>>> _seem_ OK. Actually basic
>>>>>>>> reads  are working. Its with large BC reads using an io_vec list that
>>>>>>>> the problem shows up.
>>>>>>>>
>>>>>>> Are you doing SG_IO to the sg device (/dev/sg*) or to the block device
>>>>>>> (/dev/sdX)?
>>>>>> If you are doing SG_IO to the sg device, then I know of one regression
>>>>>> (well not regression exactly, but I fixed a bug but the patch got
>>>>>> partially overwritten by another patch and that caused a new bug). Both
>>>>>> bugs are fixed in 2.6.25-rc2. Could you try that out if you are doing
>>>>>> SG_IO to the sg device.
>>>>>>
>>>>> Yes, I'm using /dev/sg*. And yes again I'll checkout 2.6.25-rc2 ASIC.
>>>>>
>>>>> Thanks
>>>>> Mark
>>>>> -
>>>>  
>>>> 2.6.25-rc2 does fix the problem I'm having. I don't suppose there is a
>>>> patch
>>>> lying around for 2.6.24.2??
>>>>
>>> I attached a backport of the patch from Tony (added as cc) that is in
>>> 2.6.25-rc2. Could you try it out against 2.6.24.2 just to make sure it
>>> was this patch, then we can send it to stable.
>>>
>>> Mark Hounschell wrote:
>>>
>>> Sorry it took so long. This does fix my problem. I hope it's not to
>>> late for 2.6.24.3
>>>
>> Backport
>> 76d78300a6eb8b7f08e47703b7e68a659ffc2053
>> to 2.6.24
> 
> Erm, I think you mean:
> 
> commit 4d2de3a50ce19af2008a90636436a1bf5b3b697b
> Author: Tony Battersby <tonyb@...ernetics.com>
> Date:   Tue Feb 5 10:36:10 2008 -0500
> 
>     [SCSI] fix BUG when sum(scatterlist) > bufflen
> 
> I can send it ... I thought the error was introduced post 2.6.24, but it
> was actually in 2.6.24-rc1
> 
> James
> 

I just cut and pasted from Mike's previous email. It would be great if this 
could get into the 2.6.24-stable tree.

Thanks
Mark

> 
>> >From Tony Battersby:
>>
>> When sending a SCSI command to a tape drive via the SCSI Generic (sg)
>> driver, if the command has a data transfer length more than
>> scatter_elem_sz (32 KB default) and not a multiple of 512, then I either
>> hit BUG_ON(!valid_dma_direction(direction)) in dma_unmap_sg() or else
>> the command never completes (depending on the LLDD).
>>
>> When constructing scatterlists, the sg driver rounds up the scatterlist
>> element sizes to be a multiple of 512.  This can result in
>> sum(scatterlist lengths) > bufflen.  In this case, scsi_req_map_sg()
>> incorrectly sets bio->bi_size to sum(scatterlist lengths) rather than to
>> bufflen.  When the command completes, req_bio_endio() detects that
>> bio->bi_size != 0, and so it doesn't call bio_endio().  This causes the
>> command to be resubmitted, resulting in BUG_ON or the command never
>> completing.
>>
>> This patch makes scsi_req_map_sg() set bio->bi_size to bufflen rather
>> than to sum(scatterlist lengths), which fixes the problem.
>>
>> Signed-off-by: Mike Christie <michaelc@...wisc.edu>
>>
>> --- linux-2.6.24.2/drivers/scsi/scsi_lib.c	2008-02-10 23:51:11.000000000
>> -0600
>> +++ linux-2.6.24.2.work/drivers/scsi/scsi_lib.c	2008-02-22
>> 16:20:09.000000000 -0600
>> @@ -298,7 +298,6 @@ static int scsi_req_map_sg(struct reques
>>  		page = sg_page(sg);
>>  		off = sg->offset;
>>  		len = sg->length;
>> - 		data_len += len;
>>
>>  		while (len > 0 && data_len > 0) {
>>  			/*
>>
>>
>> Did this ever get sent to the stable team?
>>
>> Regards
>> Mark
>> --
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> 
> 

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