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Date: Tue, 11 May 2010 16:24:58 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Dave Airlie <airlied@gmail.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>,
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Subject: Re: DRM Error on Acer Aspire One
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On Wed, 12 May 2010 09:17:09 +1000
Dave Airlie <airlied@gmail.com> wrote:

> >> >> and
> >> >> this codepath is called from non-irq contexts just as much as irq
> >> >> contexts.
> >> >
> >> > That's fine. __As long as we do a local_irq_disable(), KM_IRQ0 can be
> >> > used from both irq- and non-irq contexts. __All we need to do is to
> >> > ensure that some interrupt cannot come along on this CPU and corrupt
> >> > the slot.
> >>
> >> I don't think we do that in a lot of places, and I'd rather not add
> >> that in to fix this problem at this point in the release cycle, as
> >> we've no idea what it might break/regress.
> >
> > What is "that"? __The switch to irq-protected KM_IRQ0? __That won't break
> > anything.
> >
> 
> disabling local cpu irqs around all these kmap mappings.
> 

Ah.  Well if there are other uses of KM_USER0 from interrupt context
then yes, we have more problems.  CONFIG_DEBUG_HIGHMEM &&
CONFIG_TRACE_IRQFLAGS_SUPPORT will detect that and as long as Jaswinder
has hit all code paths in his testing, we're good.  Some manual review
for this would be good.