Date: Thu, 4 Jun 2009 16:44:24 +0900
To: bharrosh@panasas.com
Cc: fujita.tomonori@lab.ntt.co.jp, just.for.lkml@googlemail.com,
       hancockrwd@gmail.com, linux-kernel@vger.kernel.org,
       linux-scsi@vger.kernel.org
Subject: Re: sata_sil24 0000:04:00.0: DMA-API: device driver frees DMA sg
 list 	with different entry count [map count=13] [unmap count=10]
From: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
In-Reply-To: <4A277482.5070909@panasas.com>
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	<20090604153253B.fujita.tomonori@lab.ntt.co.jp>
	<4A277482.5070909@panasas.com>
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On Thu, 04 Jun 2009 10:15:14 +0300
Boaz Harrosh <bharrosh@panasas.com> wrote:

> On 06/04/2009 09:33 AM, FUJITA Tomonori wrote:
> > On Thu, 4 Jun 2009 08:12:34 +0200
> > Torsten Kaiser <just.for.lkml@googlemail.com> wrote:
> > 
> >> On Thu, Jun 4, 2009 at 2:02 AM, FUJITA Tomonori
> >> <fujita.tomonori@lab.ntt.co.jp> wrote:
> >>> On Wed, 3 Jun 2009 21:30:32 +0200
> >>> Torsten Kaiser <just.for.lkml@googlemail.com> wrote:
> >>>> Still happens with 2.6.30-rc8 (see trace at the end of the email)
> >>>>
> >>>> As orig_n_elem is only used two times in libata-core.c I suspected a
> >>>> corruption of the qc->sg, but adding checks for this did not trigger.
> >>>> So I looked into lib/dma-debug.c.
> >>>> It seems add_dma_entry() does not protect against adding the same
> >>>> entry twice.
> >>> Do you mean that add_dma_entry() doesn't protect against adding a new
> >>> entry identical to the existing entry, right?
> >> Yes, as I read the hash bucket code in lib/dma-debug.c a second entry
> >> from the same device and the same address will just be added to the
> >> list and on unmap it will always return the first entry.
> > 
> > It means that two different DMA operations will be performed against
> > the same dma addresss on the same device at the same time. It doesn't
> > happen unless there is a bug in a driver, an IOMMU or somewhere, as I
> > wrote in the previous mail.
> > 
> 
> What about the draining buffers used by libata. Are they not the same buffer
> for all devices for all requests?

I'm not sure if the drain buffer is used like that. But is there
easier ways to see the same buffer; e.g. sending the same buffer twice
with DIO?

As I wrote, I assume that he uses GART IOMMU; it allocates an unique
dma address per dma mapping operation.

However, dma-debug is broken wrt this, I guess.
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