Subject: Re: New 2.6.24.2 SG_IO SCSI problems
From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Mark Hounschell <dmarkh@cfl.rr.com>
Cc: Mike Christie <michaelc@cs.wisc.edu>, markh@compro.net,
       linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org,
       Tony Battersby <tonyb@cybernetics.com>
In-Reply-To: <47CE8AEA.1060209@cfl.rr.com>
References: <47BD9588.9080803@compro.net> <47BEFD4B.9060803@cs.wisc.edu>
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	 <47BF40D7.5050301@compro.net> <47BF4BD0.7080008@cs.wisc.edu>
	 <47CE8AEA.1060209@cfl.rr.com>
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Date: Wed, 05 Mar 2008 09:44:13 -0600
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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@cybernetics.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


> >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@cs.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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