[Intel-gfx] [CI 2/5] drm/i915/breadcrumbs: Update bottom-half before marking as complete

[Chris Wilson]

When adding a new request to the breadcrumb rbtree, we mark all those
requests inside the rbtree that are already completed as complete. This
wakes those waiters up and allows them to skip the spinlock before
returning to userspace. If one of those is the current bottom-half and
allocated its intel_wait on the stack, it may then overwrite the
b->irq_wait upon exiting i915_wait_request() just as the interrupt handler
dereferences it.

Fixes: 56299fb7d904 ("drm/i915: Signal first fence from irq handler if complete")
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
---
 drivers/gpu/drm/i915/intel_breadcrumbs.c | 36 +++++++++++++++++---------------
 1 file changed, 19 insertions(+), 17 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c
index 3f222dee4c25..f50cb1e7e145 100644
--- a/drivers/gpu/drm/i915/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
@@ -303,6 +303,7 @@ static inline void __intel_breadcrumbs_next(struct intel_engine_cs *engine,
 
 	spin_lock(&b->irq_lock);
 	GEM_BUG_ON(!b->irq_armed);
+	GEM_BUG_ON(!b->irq_wait);
 	b->irq_wait = to_wait(next);
 	spin_unlock(&b->irq_lock);
 
@@ -378,25 +379,10 @@ static bool __intel_engine_add_wait(struct intel_engine_cs *engine,
 	rb_link_node(&wait->node, parent, p);
 	rb_insert_color(&wait->node, &b->waiters);
 
-	if (completed) {
-		struct rb_node *next = rb_next(completed);
-
-		GEM_BUG_ON(!next && !first);
-		if (next && next != &wait->node) {
-			GEM_BUG_ON(first);
-			__intel_breadcrumbs_next(engine, next);
-		}
-
-		do {
-			struct intel_wait *crumb = to_wait(completed);
-			completed = rb_prev(completed);
-			__intel_breadcrumbs_finish(b, crumb);
-		} while (completed);
-	}
-
 	if (first) {
-		spin_lock(&b->irq_lock);
 		GEM_BUG_ON(rb_first(&b->waiters) != &wait->node);
+
+		spin_lock(&b->irq_lock);
 		b->irq_wait = wait;
 		/* After assigning ourselves as the new bottom-half, we must
 		 * perform a cursory check to prevent a missed interrupt.
@@ -409,7 +395,23 @@ static bool __intel_engine_add_wait(struct intel_engine_cs *engine,
 		__intel_breadcrumbs_enable_irq(b);
 		spin_unlock(&b->irq_lock);
 	}
+
+	if (completed) {
+		if (!first) {
+			struct rb_node *next = rb_next(completed);
+			GEM_BUG_ON(next == &wait->node);
+			__intel_breadcrumbs_next(engine, next);
+		}
+
+		do {
+			struct intel_wait *crumb = to_wait(completed);
+			completed = rb_prev(completed);
+			__intel_breadcrumbs_finish(b, crumb);
+		} while (completed);
+	}
+
 	GEM_BUG_ON(!b->irq_wait);
+	GEM_BUG_ON(!b->irq_armed);
 	GEM_BUG_ON(rb_first(&b->waiters) != &b->irq_wait->node);
 
 	return first;
-- 
2.11.0