Before walking the rbtree of waiters (marking them as complete and waking
them), decouple the interrupt handler. This prevents a race between the
missed waiter waking up and removing its intel_wait (which skips
checking the lock) and the interrupt handler dereferencing the
intel_wait. (Though we do not expect to encounter waiters during idle!)
Fixes: e1c0c91bdaec ("drm/i915: Wake up all waiters before idling")
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
---
drivers/gpu/drm/i915/intel_breadcrumbs.c | 15 ++++++++-------
1 file changed, 8 insertions(+), 7 deletions(-)
diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c
index f50cb1e7e145..569128e3cac2 100644
--- a/drivers/gpu/drm/i915/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
@@ -179,7 +179,7 @@ void __intel_engine_disarm_breadcrumbs(struct intel_engine_cs *engine)
void intel_engine_disarm_breadcrumbs(struct intel_engine_cs *engine)
{
struct intel_breadcrumbs *b = &engine->breadcrumbs;
- struct intel_wait *wait, *n;
+ struct intel_wait *wait, *n, *first;
if (!b->irq_armed)
return;
@@ -190,18 +190,19 @@ void intel_engine_disarm_breadcrumbs(struct intel_engine_cs *engine)
*/
spin_lock_irq(&b->rb_lock);
+
+ spin_lock(&b->irq_lock);
+ first = fetch_and_zero(&b->irq_wait);
+ __intel_engine_disarm_breadcrumbs(engine);
+ spin_unlock(&b->irq_lock);
+
rbtree_postorder_for_each_entry_safe(wait, n, &b->waiters, node) {
RB_CLEAR_NODE(&wait->node);
- if (wake_up_process(wait->tsk) && wait == b->irq_wait)
+ if (wake_up_process(wait->tsk) && wait == first)
missed_breadcrumb(engine);
}
b->waiters = RB_ROOT;
- spin_lock(&b->irq_lock);
- b->irq_wait = NULL;
- __intel_engine_disarm_breadcrumbs(engine);
- spin_unlock(&b->irq_lock);
-
spin_unlock_irq(&b->rb_lock);
}
--
2.11.0
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