linux-kernel - Re: [PATCH] firewire: fw-ohci: sync AT dma buffer before use

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Date:	Thu, 13 Mar 2008 09:49:03 +0100
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	Jarod Wilson <jwilson@...hat.com>
CC:	linux1394-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] firewire: fw-ohci: sync AT dma buffer before use

Jarod Wilson wrote:
> On Wednesday 12 March 2008 07:16:43 pm Stefan Richter wrote:
>> Jarod Wilson wrote:
>>> See http://bugzilla.kernel.org/show_bug.cgi?id=9617
>> Alas the panic from comment #10 is still there, i.e. instant crash when
>> plugging in an LSI based CD-RW (shortly after SCSI inquiry) --- but only
>> if CONFIG_DEBUG_PAGEALLOC=y.
>>
>> Jarod, did your crashes happen with CONFIG_DEBUG_PAGEALLOC=n?
> 
> No, they're with it turned on (and still on w/this change where it doesn't 
> panic). If I run with CONFIG_DEBUG_PAGEALLOC=n, no panic.

So then that's like "my" panic.

The other thing that I see here is that it only happens with my two LSI 
based devices (both CD-RWs), always quickly after SCSI inquiry.

I shall test with my Prolific based DVD-RW to find out whether it is 
about some requests that are sent to CD/DVD-RWs or about the split 
transactions that I get from the LSI bridges.  (See bugzilla.)

>> So this patch shouldn't do 
>> anything, except that it inserts a call which happens to have barrier
>> characteristics on some platforms.

...and potentially delays execution.

> ...but got lucky in that it actually helps this particular setup (x86_64 
> kernel, dual quad-core opteron, 8G RAM, 3 FireWire controllers). Hrm.

Unless you or I spot the real solution earlier, you could also try 
replacing your dma_sync_ with mb() and with mdelay() respectively to see 
what aspect of the dma_sync_ is fixing your setup.  Also move the mb() 
to other interesting places of the involved code.
-- 
Stefan Richter
-=====-==--- --== -==-=
http://arcgraph.de/sr/
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