Re: [PATCH 2/5] drm/i915/selftests: Flush the active callbacks

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On 22/11/2019 11:21, Chris Wilson wrote:
Before checking the current i915_active state for the asynchronous work
we submitted, flush any ongoing callback. This ensures that our sampling
is robust and does not sporadically fail due to bad timing as the work
is running on another cpu.

Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
---
  drivers/gpu/drm/i915/gt/selftest_context.c | 19 +++++++++++++------
  1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/selftest_context.c b/drivers/gpu/drm/i915/gt/selftest_context.c
index 3586af636304..939798338242 100644
--- a/drivers/gpu/drm/i915/gt/selftest_context.c
+++ b/drivers/gpu/drm/i915/gt/selftest_context.c
@@ -48,20 +48,25 @@ static int context_sync(struct intel_context *ce)
mutex_lock(&tl->mutex);
  	do {
-		struct dma_fence *fence;
+		struct i915_request *rq;
  		long timeout;
- fence = i915_active_fence_get(&tl->last_request);
-		if (!fence)
+		if (list_empty(&tl->requests))
  			break;
- timeout = dma_fence_wait_timeout(fence, false, HZ / 10);
+		rq = list_last_entry(&tl->requests, typeof(*rq), link);
+		i915_request_get(rq);
+
+		timeout = i915_request_wait(rq, 0, HZ / 10);
  		if (timeout < 0)
  			err = timeout;
  		else
-			i915_request_retire_upto(to_request(fence));
+			i915_request_retire_upto(rq);
- dma_fence_put(fence);
+		spin_lock_irq(&rq->lock);
+		spin_unlock_irq(&rq->lock);

Ugh.. this at least needs a comment.

What is the actual race?

Regards,

Tvrtko

+
+		i915_request_put(rq);
  	} while (!err);
  	mutex_unlock(&tl->mutex);
@@ -282,6 +287,8 @@ static int __live_active_context(struct intel_engine_cs *engine,
  		err = -EINVAL;
  	}
+ intel_engine_pm_flush(engine);
+
  	if (intel_engine_pm_is_awake(engine)) {
  		struct drm_printer p = drm_debug_printer(__func__);
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