linux-kernel - Re: USB transfer_buffer allocations on 64bit systems

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Date:	Mon, 12 Apr 2010 12:57:16 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Andi Kleen <andi@...stfloor.org>
cc:	Daniel Mack <daniel@...aq.de>, Pedro Ribeiro <pedrib@...il.com>,
	<linux-kernel@...r.kernel.org>, <akpm@...ux-foundation.org>,
	Greg KH <gregkh@...e.de>, <alsa-devel@...a-project.org>,
	<linux-usb@...r.kernel.org>
Subject: Re: USB transfer_buffer allocations on 64bit systems

On Mon, 12 Apr 2010, Andi Kleen wrote:

> On Mon, Apr 12, 2010 at 12:17:22PM -0400, Alan Stern wrote:
> > On Mon, 12 Apr 2010, Andi Kleen wrote:
> > 
> > > > Well, the sound driver itself doesn't care for any of those things, just
> > > > like any other USB driver doesn't. The USB core itself of the host
> > > > controller driver should do, and as far as I can see, it does that, yes.
> > > 
> > > Hmm, still things must go wrong somewhere. Perhaps need some instrumentation
> > > to see if all the transfer buffers really hit the PCI mapping functions.
> > 
> > Such a test has already been carried out earlier in this thread:
> > 
> > 	http://marc.info/?l=linux-usb&m=127074587029353&w=2
> > 	http://marc.info/?l=linux-usb&m=127076841801051&w=2
> > 	http://marc.info/?l=linux-usb&m=127082890510415&w=2
> 
> Hmm, thanks. But things must still go wrong somewhere, otherwise
> the GFP_DMA32 wouldn't be needed?

Indeed, something must go wrong somewhere.  Since Daniel's patch fixed
the problem by changing the buffer from a streaming mapping to a
coherent mapping, it's logical to assume that bad DMA addresses have
something to do with it.  But we don't really know for certain.

Alan Stern

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