[Intel-gfx] [PATCH 2/6] drm/i915: Check current i915_vma.pin_count status first on unbind

[Chris Wilson]

Quoting Tvrtko Ursulin (2020-01-27 14:15:57)
> 
> On 26/01/2020 10:23, Chris Wilson wrote:
> > Do an early rejection of a i915_vma_unbind() attempt if the i915_vma is
> > currently pinned, without waiting to see if the inflight operations may
> > unpin it. We see this problem with the shrinker trying to unbind the
> > active vma from inside its bind worker:
> 
> What is the actual problem? flush_work from a worker?

We hit the shrinker from the inside the worker (which is intended). But
what is not intended is for the shrinker to wait on any of the workers,
because of the potential recursion of waiting on one's self. The
intention was that we avoid the shrinker waiting on the vma by keeping
the vma pinned... But I only pinned the pages to prevent them being
freed and not the worker to prevent the recursive wait.

Heh.
-Chris