[Intel-gfx] [PATCH 2/2] drm/i915/execlists: Skip nested spinlock for validating pending

[Chris Wilson]

Quoting Chris Wilson (2019-12-03 15:26:31)
> Only along the submission path can we guarantee that the locked request
> is indeed from a foreign engine, and so the nesting of engine/rq is
> permissible. On the submission tasklet (process_csb()), we may find
> ourselves competing with the normal nesting of rq/engine, invalidating
> our nesting. As we only use the spinlock for debug purposes, skip the
> debug if we cannot acquire the spinlock for safe validation - catching
> 99% of the bugs is better than causing a hard lockup.
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
-Chris