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Commit cced5e2f authored by Chris Wilson's avatar Chris Wilson
Browse files

drm/i915: Take a reference whilst processing the signaler request 



The plan in the near-future is to allow requests to be removed from the
signaler. We can no longer then rely on holding a reference to the
request for the duration it is in the signaling tree, and instead must
obtain a reference to the request for the current operation using RCU.

Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: default avatarTvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-10-chris@chris-wilson.co.uk
parent 754c9fd5

drivers/gpu/drm/i915/intel_breadcrumbs.c

+15 −7
Original line number Diff line number Diff line
@@ -496,7 +496,11 @@ static int intel_breadcrumbs_signaler(void *arg) 
		 * need to wait for a new interrupt from the GPU or for

		 * a new client.

		 */

		request = READ_ONCE(b->first_signal);

		rcu_read_lock();

		request = rcu_dereference(b->first_signal);

		if (request)

			request = i915_gem_request_get_rcu(request);

		rcu_read_unlock();

		if (signal_complete(request)) {

			local_bh_disable();

			dma_fence_signal(&request->fence);
@@ -515,24 +519,28 @@ static int intel_breadcrumbs_signaler(void *arg) 
			 * the oldest before picking the next one.

			 */

			spin_lock_irq(&b->lock);

			if (request == b->first_signal) {

			if (request == rcu_access_pointer(b->first_signal)) {

				struct rb_node *rb =

					rb_next(&request->signaling.node);

				b->first_signal = rb ? to_signaler(rb) : NULL;

				rcu_assign_pointer(b->first_signal,

						   rb ? to_signaler(rb) : NULL);

			}

			rb_erase(&request->signaling.node, &b->signals);

			spin_unlock_irq(&b->lock);



			i915_gem_request_put(request);

		} else {

			if (kthread_should_stop())

			if (kthread_should_stop()) {

				GEM_BUG_ON(request);

				break;

			}



			schedule();



			if (kthread_should_park())

				kthread_parkme();

		}

		i915_gem_request_put(request);

	} while (1);

	__set_current_state(TASK_RUNNING);
@@ -597,7 +605,7 @@ void intel_engine_enable_signaling(struct drm_i915_gem_request *request) 
	rb_link_node(&request->signaling.node, parent, p);

	rb_insert_color(&request->signaling.node, &b->signals);

	if (first)

		smp_store_mb(b->first_signal, request);

		rcu_assign_pointer(b->first_signal, request);



	spin_unlock(&b->lock);
@@ -670,7 +678,7 @@ void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine) 
	/* The engines should be idle and all requests accounted for! */

	WARN_ON(READ_ONCE(b->first_wait));

	WARN_ON(!RB_EMPTY_ROOT(&b->waiters));

	WARN_ON(READ_ONCE(b->first_signal));

	WARN_ON(rcu_access_pointer(b->first_signal));

	WARN_ON(!RB_EMPTY_ROOT(&b->signals));



	if (!IS_ERR_OR_NULL(b->signaler))
@@ -691,7 +699,7 @@ bool intel_breadcrumbs_busy(struct intel_engine_cs *engine) 
		busy |= intel_engine_flag(engine);

	}



	if (b->first_signal) {

	if (rcu_access_pointer(b->first_signal)) {

		wake_up_process(b->signaler);

		busy |= intel_engine_flag(engine);

	}

drivers/gpu/drm/i915/intel_ringbuffer.h

+1 −1
Original line number Diff line number Diff line
@@ -242,7 +242,7 @@ struct intel_engine_cs { 
		struct rb_root signals; /* sorted by retirement */

		struct intel_wait *first_wait; /* oldest waiter by retirement */

		struct task_struct *signaler; /* used for fence signalling */

		struct drm_i915_gem_request *first_signal;

		struct drm_i915_gem_request __rcu *first_signal;

		struct timer_list fake_irq; /* used after a missed interrupt */

		struct timer_list hangcheck; /* detect missed interrupts */