drm/i915: Hold irq-off for the entire fake lock period

Sadly lockdep records when the irqs are re-enabled and then marks up the
fake lock as being irq-unsafe. Our hand is forced and so we must mark up
the entire fake lock critical section as irq-off.

Hopefully this is the last tweak required!

v2: Not quite, we need to mark the timeline spinlock as irqsafe. That
was a genuine bug being hidden by the earlier lockdep splat.

Fixes: d67739268cf0 ("drm/i915/gt: Mark up the nested engine-pm timeline lock as irqsafe")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190823132700.25286-2-chris@chris-wilson.co.uk

1 files changed, 6 insertions, 4 deletions

diff --git a/drivers/gpu/drm/i915/gt/intel_timeline.c b/drivers/gpu/drm/i915/gt/intel_timeline.c
index 02fbe11b671b..9cb01d9828f1 100644
--- a/drivers/gpu/drm/i915/gt/intel_timeline.c
+++ b/drivers/gpu/drm/i915/gt/intel_timeline.c
@@ -337,6 +337,7 @@ int intel_timeline_pin(struct intel_timeline *tl)
 void intel_timeline_enter(struct intel_timeline *tl)
 {
 	struct intel_gt_timelines *timelines = &tl->gt->timelines;
+	unsigned long flags;
 
 	lockdep_assert_held(&tl->mutex);
 
@@ -345,14 +346,15 @@ void intel_timeline_enter(struct intel_timeline *tl)
 		return;
 	GEM_BUG_ON(!tl->active_count); /* overflow? */
 
-	spin_lock(&timelines->lock);
+	spin_lock_irqsave(&timelines->lock, flags);
 	list_add(&tl->link, &timelines->active_list);
-	spin_unlock(&timelines->lock);
+	spin_unlock_irqrestore(&timelines->lock, flags);
 }
 
 void intel_timeline_exit(struct intel_timeline *tl)
 {
 	struct intel_gt_timelines *timelines = &tl->gt->timelines;
+	unsigned long flags;
 
 	lockdep_assert_held(&tl->mutex);
 
@@ -360,9 +362,9 @@ void intel_timeline_exit(struct intel_timeline *tl)
 	if (--tl->active_count)
 		return;
 
-	spin_lock(&timelines->lock);
+	spin_lock_irqsave(&timelines->lock, flags);
 	list_del(&tl->link);
-	spin_unlock(&timelines->lock);
+	spin_unlock_irqrestore(&timelines->lock, flags);
 
 	/*
 	 * Since this timeline is idle, all bariers upon which we were waiting