[Intel-gfx] [PATCH] drm/i915: Prefer to reschedule the free_object worker rather than block

[Chris Wilson]

Avoid blocking the kworker by putting back the freed object list if we
cannot immediately take the mutex. We will try again shortly, and flush
the work when desperate.

References: https://bugs.freedesktop.org/show_bug.cgi?id=100434
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index ab77e38ec264..c2e5cb529b0f 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -4200,7 +4200,19 @@ static void __i915_gem_free_objects(struct drm_i915_private *i915,
 {
 	struct drm_i915_gem_object *obj, *on;
 
-	mutex_lock(&i915->drm.struct_mutex);
+	if (!mutex_trylock(&i915->drm.struct_mutex)) {
+		/* If we fail to acquire the struct_mutex, put back the
+		 * freed list and we will try again in the future. By
+		 * rescheduling the task we prevent us from blocking
+		 * the worker indefinitely on a prolonged wait for
+		 * struct_mutex.
+		 */
+		if (llist_add_batch(llist_reverse_order(freed), freed,
+				    &i915->mm.free_list))
+			schedule_work(&i915->mm.free_work);
+		return;
+	}
+
 	intel_runtime_pm_get(i915);
 	llist_for_each_entry(obj, freed, freed) {
 		struct i915_vma *vma, *vn;
-- 
2.11.0