Subject: Re: [PATCH] fix __mod_timer vs __run_timers deadlock.
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: "David S. Miller" <davem@davemloft.net>
Cc: paulus@samba.org, jk@blackdown.de, akpm@osdl.org, oleg@tv-sign.ru,
       linux-kernel@vger.kernel.org, maneesh@in.ibm.com
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Date: Wed, 04 May 2005 10:05:08 +1000
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On Tue, 2005-05-03 at 16:39 -0700, David S. Miller wrote:
> On Wed, 04 May 2005 09:44:53 +1000
> Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote:
> 
> > Nothing prevents it ? well, I wouldn't be that optimistic :) The USB
> > stuff is a bit complex, it inlcudes doing DMAs, so manipulating the
> > iommu, dealing with URB queues (and thus allocating/releasing them)
> > etc... and especially in the context of xmon, that mean letting the
> > driver do a lot of these at any time whatever state the system is...
> 
> I think doing calls to the USB interrupt handler would work.
> I'm not being crazy :)

Maybe, but it will trigger all other USB drivers around and really
weird things might happen.. Oh well, I may give it a try one of
these days anyway. I could probably even do some hack to force the
OHCI to only service incoming interrupt URBs for input devices or
such things...

> But yeah we could do a micro-stack as well, but as you noted the
> transfer to/from the real USB HCI driver would be non-trivial.
> 
> I truly believe just calling the real USB HCI driver interrupt
> handler in a polling fashion is the way to go.

But it feels very fragile... Oh well, I will experiment with that one of
these days (no time right now though).

Ben.


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