[Intel-gfx] [PATCH 2/2] drm/i915: Initialise userptr mmu_notifier serial to 1

[Chris Wilson]

On Fri, Jul 11, 2014 at 12:31:12PM +0100, Tvrtko Ursulin wrote:
> 
> On 07/11/2014 12:06 PM, Chris Wilson wrote:
> >On Fri, Jul 11, 2014 at 12:00:26PM +0100, Tvrtko Ursulin wrote:
> >>But it will be interesting to know what code managed to trigger this
> >>race, because as we discussed on IRC it would indicate some pretty
> >>wild userspace behaviour. Or lack of imagination on our part?
> >
> >A threaded client. One thread using userptr, the other doing munmap or
> >free. Given enough embarrassment, it will happen every time.
> 
> Yes fine, but I struggle to imagine what would be the intention of
> such code or how did it manage to fail in such way. I hope the only
> difference is not that userptr "upgraded" the failure mode for heap
> corruption or memory management races in general.

The mmu notifier is called everytime a process sneezes. It does not
imply that our object is being invalidated, just that some portion of
the current->mm is being modified.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre