[Intel-gfx] [PATCH] drm/i915: Unwind partial VMA rebinding after failure in set-cache-level

[Chris Wilson]

If the impossible happens and we fail to rebind a VMA in the middle of
rebinding all VMA for an object we currently bail out and leave the
object in an inconsistent state. Attempt to unwind the incomplete update
by reverting all updated VMA back to the original cache-level, and WARN
if that fails.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem.c | 35 ++++++++++++++++++++++++++---------
 1 file changed, 26 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 1e67484fd5dc..24ba47a22260 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -3664,6 +3664,12 @@ int i915_gem_object_set_cache_level(struct drm_i915_gem_object *obj,
 	struct i915_vma *vma, *next;
 	int ret = 0;
 
+	/* We manipulate all the PTEs in the various GTT associated with
+	 * this object which requires that the caller takes the
+	 * struct_mutex on our behalf.
+	 */
+	lockdep_assert_held(&dev->struct_mutex);
+
 	if (obj->cache_level == cache_level)
 		goto out;
 
@@ -3697,17 +3703,18 @@ int i915_gem_object_set_cache_level(struct drm_i915_gem_object *obj,
 				return ret;
 		}
 
-		list_for_each_entry(vma, &obj->vma_list, vma_link)
-			if (drm_mm_node_allocated(&vma->node)) {
-				ret = i915_vma_bind(vma, cache_level,
-						    PIN_UPDATE);
-				if (ret)
-					return ret;
-			}
+		list_for_each_entry(vma, &obj->vma_list, vma_link) {
+			if (!drm_mm_node_allocated(&vma->node))
+				continue;
+
+			ret = i915_vma_bind(vma, cache_level, PIN_UPDATE);
+			if (ret)
+				goto unwind;
+
+			vma->node.color = cache_level;
+		}
 	}
 
-	list_for_each_entry(vma, &obj->vma_list, vma_link)
-		vma->node.color = cache_level;
 	obj->cache_level = cache_level;
 
 out:
@@ -3719,6 +3726,16 @@ out:
 	}
 
 	return 0;
+
+unwind:
+	list_for_each_entry_continue_reverse(vma, &obj->vma_list, vma_link) {
+		if (!drm_mm_node_allocated(&vma->node))
+			continue;
+
+		WARN_ON(i915_vma_bind(vma, obj->cache_level, PIN_UPDATE));
+		vma->node.color = obj->cache_level;
+	}
+	return ret;
 }
 
 int i915_gem_get_caching_ioctl(struct drm_device *dev, void *data,
-- 
2.6.1