[Intel-gfx] [PATCH] drm/i915/selftests: add some vma_sync

[Matthew Auld]

On Mon, 23 Mar 2020 at 11:43, Chris Wilson <chris at chris-wilson.co.uk> wrote:
>
> Quoting Matthew Auld (2020-03-23 11:38:09)
> > The subtest shrink_boom was added as a regression test for some missing
> > refcounting on the paging structures, however since the binding is
> > potentially async, setting the vm->fault_attr might apply to the purge
> > vma, and not the intended explode vma.
>
> Hmm. Sounds a fair point, though let's see if that is not an unintended
> bonus.
>
> > Also it looks like it might also
> > be possible to hit some weird shrinker deadlock where the unbinding of
> > one vma allocates memory by flushing and waiting for its
> > still-pending-bind operation while holding vm->mutex, which will always
> > lands back in the shrinker since we set vm->fault_attr for the selftest.
>
> However that is a bug we have to handle. And it should be prevented
> currently by avoiding shrinking active (still being bound) vma, e.g.
> 6f24e41022f2 ("drm/i915: Avoid recursing onto active vma from the
> shrinker"). So is that a current observation?

Missed that. Egg-on-face.

> -Chris
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