[2/2] drm/i915/execlists: Skip nested spinlock for validating pending
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Message ID 20191203152631.3107653-2-chris@chris-wilson.co.uk
State New
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Series
  • [1/2] drm/i915/execlists: Add a couple more validity checks to assert_pending()
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Commit Message

Chris Wilson Dec. 3, 2019, 3:26 p.m. UTC
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>
---
 drivers/gpu/drm/i915/gt/intel_lrc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Comments

Chris Wilson Dec. 3, 2019, 3:37 p.m. UTC | #1
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.
> 
Fixes: c95d31c3df1b ("drm/i915/execlists: Lock the request while validating it during promotion")
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
-Chris
Chris Wilson Dec. 3, 2019, 3:41 p.m. UTC | #2
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@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
-Chris

Patch
diff mbox series

diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
index 37ab9742abe7..82807918382d 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -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;