[Intel-gfx] [PATCH 1/2] drm/i915: Objects on the unbound list may still have an active reference

[Chris Wilson]

Due to the lazy retirement semantics, even though we have unbound an
object, it may still hold onto an active reference. So in te debug code,
play safe.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_debugfs.c | 31 ++++++++++++++++++++++++++-----
 1 file changed, 26 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 2cbc85f3b237..d6c29dc6aacc 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -3826,7 +3826,6 @@ i915_drop_caches_set(void *data, u64 val)
 {
 	struct drm_device *dev = data;
 	struct drm_i915_private *dev_priv = dev->dev_private;
-	struct drm_i915_gem_object *obj, *next;
 	int ret;
 
 	DRM_DEBUG("Dropping caches: 0x%08llx\n", val);
@@ -3847,10 +3846,18 @@ i915_drop_caches_set(void *data, u64 val)
 		i915_gem_retire_requests(dev);
 
 	if (val & DROP_BOUND) {
-		list_for_each_entry_safe(obj, next, &dev_priv->mm.bound_list,
-					 global_list) {
+		struct list_head still_in_list;
+
+		INIT_LIST_HEAD(&still_in_list);
+		while (!list_empty(&dev_priv->mm.bound_list)) {
+			struct drm_i915_gem_object *obj;
 			struct i915_vma *vma, *v;
 
+			obj = list_first_entry(&dev_priv->mm.bound_list,
+					       typeof(*obj), global_list);
+
+			list_move_tail(&obj->global_list, &still_in_list);
+
 			ret = 0;
 			drm_gem_object_reference(&obj->base);
 			list_for_each_entry_safe(vma, v, &obj->vma_list, vma_link) {
@@ -3865,16 +3872,30 @@ i915_drop_caches_set(void *data, u64 val)
 			if (ret)
 				goto unlock;
 		}
+
+		list_splice(&still_in_list, &dev_priv->mm.bound_list);
 	}
 
 	if (val & DROP_UNBOUND) {
-		list_for_each_entry_safe(obj, next, &dev_priv->mm.unbound_list,
-					 global_list)
+		struct list_head still_in_list;
+
+		INIT_LIST_HEAD(&still_in_list);
+		while (!list_empty(&dev_priv->mm.unbound_list)) {
+			struct drm_i915_gem_object *obj;
+
+			obj = list_first_entry(&dev_priv->mm.unbound_list,
+					       typeof(*obj), global_list);
+
+			list_move_tail(&obj->global_list, &still_in_list);
+
 			if (obj->pages_pin_count == 0) {
 				ret = i915_gem_object_put_pages(obj);
 				if (ret)
 					goto unlock;
 			}
+		}
+
+		list_splice(&still_in_list, &dev_priv->mm.unbound_list);
 	}
 
 unlock:
-- 
2.1.0