Date: Tue, 26 Feb 2008 15:08:45 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Mike Galbraith <efault@gmx.de>
Cc: Jens Axboe <jens.axboe@oracle.com>, LKML <linux-kernel@vger.kernel.org>,
       Tejun Heo <htejun@gmail.com>, linux-ide@vger.kernel.org,
       linux-scsi@vger.kernel.org
Subject: Re: regression: CD burning (k3b) went broke
Message-Id: <20080226150845.2196bc1a.akpm@linux-foundation.org>
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On Tue, 26 Feb 2008 14:36:43 +0100 Mike Galbraith <efault@gmx.de> wrote:

> 
> On Tue, 2008-02-26 at 10:48 +0100, Mike Galbraith wrote:
> > Greetings,
> > 
> > I straced both a good and a bad kernel (good being .git with attached
> > revert patch applied) and filtered/diffed/merged the output.  Scroll
> > down to "HERE" to see the problem (resid).
> > 
> > I'm poking around, but not having much luck.

cc's added.

I'm told this is part of "Tejun's DMA drain handling".

> Seems the problem is data_len changes, but raw_data_len doesn't.  I've
> not the foggiest IO-land clue, but k3b works again, so the below may
> have some diagnostic value.

So this change fixes a bug?  Can we have a recap of how it does this?

> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index ba21d97..7a6f784 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -871,7 +871,7 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
>  			scsi_end_bidi_request(cmd);
>  			return;
>  		}
> -		req->data_len = scsi_get_resid(cmd);
> +		req->data_len = req->raw_data_len = scsi_get_resid(cmd);
>  	}
>  
>  	BUG_ON(blk_bidi_rq(req)); /* bidi not support for !blk_pc_request yet */
> 

Thanks.
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