drm/i915/gt: Move the breadcrumb to the signaler if completed upon cancel

If while we are cancelling the breadcrumb signaling, we find that the
request is already completed, move it to the irq signaler and let it be
signaled.

v2: Tweak reference counting so that we only acquire a new reference on
adding to a signal list, as opposed to a hidden i915_request_put of the
caller's reference.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201126140407.31952-5-chris@chris-wilson.co.uk

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

@@ -192,18 +192,6 @@ static void add_retire(struct intel_breadcrumbs *b, struct intel_timeline *tl)
 		intel_engine_add_retire(b->irq_engine, tl);
 }
 
-static bool __signal_request(struct i915_request *rq)
-{
-	GEM_BUG_ON(test_bit(I915_FENCE_FLAG_SIGNAL, &rq->fence.flags));
-
-	if (!__dma_fence_signal(&rq->fence)) {
-		i915_request_put(rq);
-		return false;
-	}
-
-	return true;
-}
-
 static struct llist_node *
 slist_add(struct llist_node *node, struct llist_node *head)
 {
@@ -274,9 +262,11 @@ static void signal_irq_work(struct irq_work *work)
 			release = remove_signaling_context(b, ce);
 			spin_unlock(&ce->signal_lock);
 
-			if (__signal_request(rq))
+			if (__dma_fence_signal(&rq->fence))
 				/* We own signal_node now, xfer to local list */
 				signal = slist_add(&rq->signal_node, signal);
+			else
+				i915_request_put(rq);
 
 			if (release) {
 				add_retire(b, ce->timeline);
@@ -363,6 +353,17 @@ void intel_breadcrumbs_free(struct intel_breadcrumbs *b)
 	kfree(b);
 }
 
+static void irq_signal_request(struct i915_request *rq,
+			       struct intel_breadcrumbs *b)
+{
+	if (!__dma_fence_signal(&rq->fence))
+		return;
+
+	i915_request_get(rq);
+	if (llist_add(&rq->signal_node, &b->signaled_requests))
+		irq_work_queue(&b->irq_work);
+}
+
 static void insert_breadcrumb(struct i915_request *rq)
 {
 	struct intel_breadcrumbs *b = READ_ONCE(rq->engine)->breadcrumbs;
@@ -372,17 +373,13 @@ static void insert_breadcrumb(struct i915_request *rq)
 	if (test_bit(I915_FENCE_FLAG_SIGNAL, &rq->fence.flags))
 		return;
 
-	i915_request_get(rq);
-
 	/*
 	 * If the request is already completed, we can transfer it
 	 * straight onto a signaled list, and queue the irq worker for
 	 * its signal completion.
 	 */
 	if (__request_completed(rq)) {
-		if (__signal_request(rq) &&
-		    llist_add(&rq->signal_node, &b->signaled_requests))
-			irq_work_queue(&b->irq_work);
+		irq_signal_request(rq, b);
 		return;
 	}
 
@@ -413,6 +410,8 @@ static void insert_breadcrumb(struct i915_request *rq)
 				break;
 		}
 	}
+
+	i915_request_get(rq);
 	list_add_rcu(&rq->signal_link, pos);
 	GEM_BUG_ON(!check_signal_order(ce, rq));
 	GEM_BUG_ON(test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &rq->fence.flags));
@@ -453,6 +452,7 @@ bool i915_request_enable_breadcrumb(struct i915_request *rq)
 
 void i915_request_cancel_breadcrumb(struct i915_request *rq)
 {
+	struct intel_breadcrumbs *b = READ_ONCE(rq->engine)->breadcrumbs;
 	struct intel_context *ce = rq->context;
 	bool release;
 
@@ -461,11 +461,14 @@ void i915_request_cancel_breadcrumb(struct i915_request *rq)
 
 	spin_lock(&ce->signal_lock);
 	list_del_rcu(&rq->signal_link);
-	release = remove_signaling_context(rq->engine->breadcrumbs, ce);
+	release = remove_signaling_context(b, ce);
 	spin_unlock(&ce->signal_lock);
 	if (release)
 		intel_context_put(ce);
 
+	if (__request_completed(rq))
+		irq_signal_request(rq, b);
+
 	i915_request_put(rq);
 }