[Intel-gfx] [PATCH] drm/i915: Check the target has not already completed before waiting on it

[Chris Wilson]

When we want to wait for a request to be executed, we first ask if it is
not on the GPU  as if it's on the gpu, there's no need to wait. However,
we have to take into account that a request may not be on the GPU
because it has already completed!

The window is small due to the numerous preceding checks that our target
has not yet completed, yet there is still a very small window across the
kmalloc.

Fixes: e88619646971 ("drm/i915: Use HW semaphores for inter-engine synchronisation on gen8+")
Testcase: igt/gem_concurrent_blit
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
---
 drivers/gpu/drm/i915/i915_request.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
index d06c45305b03..6dbf8dc5cd6a 100644
--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/drivers/gpu/drm/i915/i915_request.c
@@ -373,7 +373,7 @@ i915_request_await_execution(struct i915_request *rq,
 	init_irq_work(&cb->work, irq_execute_cb);
 
 	spin_lock_irq(&signal->lock);
-	if (i915_request_is_active(signal)) {
+	if (i915_request_is_active(signal) || i915_request_completed(signal)) {
 		i915_sw_fence_complete(cb->fence);
 		kmem_cache_free(global.slab_execute_cbs, cb);
 	} else {
-- 
2.20.1