Commit bab0557c authored by Chris Wilson's avatar Chris Wilson
Browse files

drm/i915/gt: Remove virtual breadcrumb before transfer 



The issue with stale virtual breadcrumbs remain. Now we have the problem
that if the irq-signaler is still referencing the stale breadcrumb as we
transfer it to a new sibling, the list becomes spaghetti. This is a very
small window, but that doesn't stop it being hit infrequently. To
prevent the lists being tangled (the iterator starting on one engine's
b->signalers but walking onto another list), always decouple the virtual
breadcrumb on schedule-out and make sure that the walker has stepped out
of the lists.

Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: default avatarMatthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201224135544.1713-5-chris@chris-wilson.co.uk
parent 6f0726b4

drivers/gpu/drm/i915/gt/intel_breadcrumbs.c

+3 −2
Original line number Diff line number Diff line
@@ -451,15 +451,16 @@ void i915_request_cancel_breadcrumb(struct i915_request *rq) 
{

	struct intel_breadcrumbs *b = READ_ONCE(rq->engine)->breadcrumbs;

	struct intel_context *ce = rq->context;

	unsigned long flags;

	bool release;



	if (!test_and_clear_bit(I915_FENCE_FLAG_SIGNAL, &rq->fence.flags))

		return;



	spin_lock(&ce->signal_lock);

	spin_lock_irqsave(&ce->signal_lock, flags);

	list_del_rcu(&rq->signal_link);

	release = remove_signaling_context(b, ce);

	spin_unlock(&ce->signal_lock);

	spin_unlock_irqrestore(&ce->signal_lock, flags);

	if (release)

		intel_context_put(ce);

drivers/gpu/drm/i915/gt/intel_execlists_submission.c

+15 −0
Original line number Diff line number Diff line
@@ -581,6 +581,21 @@ static inline void execlists_schedule_in(struct i915_request *rq, int idx) 
static void kick_siblings(struct i915_request *rq, struct intel_context *ce)

{

	struct virtual_engine *ve = container_of(ce, typeof(*ve), context);

	struct intel_engine_cs *engine = rq->engine;



	/* Flush concurrent rcu iterators in signal_irq_work */

	if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &rq->fence.flags)) {

		/*

		 * After this point, the rq may be transferred to a new

		 * sibling, so before we clear ce->inflight make sure that

		 * the context has been removed from the b->signalers and

		 * furthermore we need to make sure that the concurrent

		 * iterator in signal_irq_work is no longer following

		 * ce->signal_link.

		 */

		i915_request_cancel_breadcrumb(rq);

		irq_work_sync(&engine->breadcrumbs->irq_work);

	}



	if (READ_ONCE(ve->request))

		tasklet_hi_schedule(&ve->base.execlists.tasklet);