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

[Stefan Richter]

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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