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drm/i915/execlists: Skip nested spinlock for validating pending

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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@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Fixes: c95d31c3df ("drm/i915/execlists: Lock the request while validating it during promotion")
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191203152631.3107653-2-chris@chris-wilson.co.uk
This commit is contained in:
Chris Wilson 2019-12-03 15:26:31 +00:00
parent 80aac91b27
commit 49e74c8f9a
1 changed files with 2 additions and 2 deletions
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4
drivers/gpu/drm/i915/gt/intel_lrc.c
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@ -1315,8 +1315,8 @@ assert_pending_valid(const struct intel_engine_execlists *execlists,
ce = rq->hw_context;
/* Hold tightly onto the lock to prevent concurrent retires! */
spin_lock_irqsave_nested(&rq->lock, flags,
SINGLE_DEPTH_NESTING);
if (!spin_trylock_irqsave(&rq->lock, flags))
continue;
if (i915_request_completed(rq))
goto unlock;