drm/i915: Avoid unbinding due to an interrupted pin_and_fence during execbuffer

If we need to stall in order to complete the pin_and_fence operation
during execbuffer reservation, there is a high likelihood that the
operation will be interrupted by a signal (thanks X!). In order to
simplify the cleanup along that error path, the object was
unconditionally unbound and the error propagated. However, being
interrupted here is far more common than I would like and so we can
strive to avoid the extra work by eliminating the forced unbind.

v2: In discussion over the indecent colour of the new functions and
unwind path, we realised that we can use the new unreserve function to
clean up the code even further.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_execbuffer.c

@@ -331,7 +331,8 @@ i915_gem_execbuffer_relocate(struct drm_device *dev,
 	return ret;
 }
 
-#define  __EXEC_OBJECT_HAS_FENCE (1<<31)
+#define  __EXEC_OBJECT_HAS_PIN (1<<31)
+#define  __EXEC_OBJECT_HAS_FENCE (1<<30)
 
 static int
 need_reloc_mappable(struct drm_i915_gem_object *obj)
@@ -341,9 +342,10 @@ need_reloc_mappable(struct drm_i915_gem_object *obj)
 }
 
 static int
-pin_and_fence_object(struct drm_i915_gem_object *obj,
+i915_gem_execbuffer_reserve_object(struct drm_i915_gem_object *obj,
 				   struct intel_ring_buffer *ring)
 {
+	struct drm_i915_private *dev_priv = obj->base.dev->dev_private;
 	struct drm_i915_gem_exec_object2 *entry = obj->exec_entry;
 	bool has_fenced_gpu_access = INTEL_INFO(ring->dev)->gen < 4;
 	bool need_fence, need_mappable;
@@ -359,11 +361,13 @@ pin_and_fence_object(struct drm_i915_gem_object *obj,
 	if (ret)
 		return ret;
 
+	entry->flags |= __EXEC_OBJECT_HAS_PIN;
+
 	if (has_fenced_gpu_access) {
 		if (entry->flags & EXEC_OBJECT_NEEDS_FENCE) {
 			ret = i915_gem_object_get_fence(obj);
 			if (ret)
-				goto err_unpin;
+				return ret;
 
 			if (i915_gem_object_pin_fence(obj))
 				entry->flags |= __EXEC_OBJECT_HAS_FENCE;
@@ -372,12 +376,35 @@ pin_and_fence_object(struct drm_i915_gem_object *obj,
 		}
 	}
 
+	/* Ensure ppgtt mapping exists if needed */
+	if (dev_priv->mm.aliasing_ppgtt && !obj->has_aliasing_ppgtt_mapping) {
+		i915_ppgtt_bind_object(dev_priv->mm.aliasing_ppgtt,
+				       obj, obj->cache_level);
+
+		obj->has_aliasing_ppgtt_mapping = 1;
+	}
+
 	entry->offset = obj->gtt_offset;
 	return 0;
+}
+
+static void
+i915_gem_execbuffer_unreserve_object(struct drm_i915_gem_object *obj)
+{
+	struct drm_i915_gem_exec_object2 *entry;
+
+	if (!obj->gtt_space)
+		return;
 
-err_unpin:
+	entry = obj->exec_entry;
+
+	if (entry->flags & __EXEC_OBJECT_HAS_FENCE)
+		i915_gem_object_unpin_fence(obj);
+
+	if (entry->flags & __EXEC_OBJECT_HAS_PIN)
 		i915_gem_object_unpin(obj);
-	return ret;
+
+	entry->flags &= ~(__EXEC_OBJECT_HAS_FENCE | __EXEC_OBJECT_HAS_PIN);
 }
 
 static int
@@ -385,11 +412,10 @@ i915_gem_execbuffer_reserve(struct intel_ring_buffer *ring,
 			    struct drm_file *file,
 			    struct list_head *objects)
 {
-	drm_i915_private_t *dev_priv = ring->dev->dev_private;
 	struct drm_i915_gem_object *obj;
-	int ret, retry;
-	bool has_fenced_gpu_access = INTEL_INFO(ring->dev)->gen < 4;
 	struct list_head ordered_objects;
+	bool has_fenced_gpu_access = INTEL_INFO(ring->dev)->gen < 4;
+	int retry;
 
 	INIT_LIST_HEAD(&ordered_objects);
 	while (!list_empty(objects)) {
@@ -427,12 +453,12 @@ i915_gem_execbuffer_reserve(struct intel_ring_buffer *ring,
 	 * 2.  Bind new objects.
 	 * 3.  Decrement pin count.
 	 *
-	 * This avoid unnecessary unbinding of later objects in order to makr
+	 * This avoid unnecessary unbinding of later objects in order to make
 	 * room for the earlier objects *unless* we need to defragment.
 	 */
 	retry = 0;
 	do {
-		ret = 0;
+		int ret = 0;
 
 		/* Unbind any ill-fitting objects or pin. */
 		list_for_each_entry(obj, objects, exec_list) {
@@ -452,7 +478,7 @@ i915_gem_execbuffer_reserve(struct intel_ring_buffer *ring,
 			    (need_mappable && !obj->map_and_fenceable))
 				ret = i915_gem_object_unbind(obj);
 			else
-				ret = pin_and_fence_object(obj, ring);
+				ret = i915_gem_execbuffer_reserve_object(obj, ring);
 			if (ret)
 				goto err;
 		}
@@ -462,46 +488,14 @@ i915_gem_execbuffer_reserve(struct intel_ring_buffer *ring,
 			if (obj->gtt_space)
 				continue;
 
-			ret = pin_and_fence_object(obj, ring);
-			if (ret) {
-				int ret_ignore;
-
-				/* This can potentially raise a harmless
-				 * -EINVAL if we failed to bind in the above
-				 * call. It cannot raise -EINTR since we know
-				 * that the bo is freshly bound and so will
-				 * not need to be flushed or waited upon.
-				 */
-				ret_ignore = i915_gem_object_unbind(obj);
-				(void)ret_ignore;
-				WARN_ON(obj->gtt_space);
-				break;
-			}
-		}
-
-		/* Decrement pin count for bound objects */
-		list_for_each_entry(obj, objects, exec_list) {
-			struct drm_i915_gem_exec_object2 *entry;
-
-			if (!obj->gtt_space)
-				continue;
-
-			entry = obj->exec_entry;
-			if (entry->flags & __EXEC_OBJECT_HAS_FENCE) {
-				i915_gem_object_unpin_fence(obj);
-				entry->flags &= ~__EXEC_OBJECT_HAS_FENCE;
+			ret = i915_gem_execbuffer_reserve_object(obj, ring);
+			if (ret)
+				goto err;
 		}
 
-			i915_gem_object_unpin(obj);
-
-			/* ... and ensure ppgtt mapping exist if needed. */
-			if (dev_priv->mm.aliasing_ppgtt && !obj->has_aliasing_ppgtt_mapping) {
-				i915_ppgtt_bind_object(dev_priv->mm.aliasing_ppgtt,
-						       obj, obj->cache_level);
-
-				obj->has_aliasing_ppgtt_mapping = 1;
-			}
-		}
+err:		/* Decrement pin count for bound objects */
+		list_for_each_entry(obj, objects, exec_list)
+			i915_gem_execbuffer_unreserve_object(obj);
 
 		if (ret != -ENOSPC || retry++)
 			return ret;
@@ -510,24 +504,6 @@ i915_gem_execbuffer_reserve(struct intel_ring_buffer *ring,
 		if (ret)
 			return ret;
 	} while (1);
-
-err:
-	list_for_each_entry_continue_reverse(obj, objects, exec_list) {
-		struct drm_i915_gem_exec_object2 *entry;
-
-		if (!obj->gtt_space)
-			continue;
-
-		entry = obj->exec_entry;
-		if (entry->flags & __EXEC_OBJECT_HAS_FENCE) {
-			i915_gem_object_unpin_fence(obj);
-			entry->flags &= ~__EXEC_OBJECT_HAS_FENCE;
-		}
-
-		i915_gem_object_unpin(obj);
-	}
-
-	return ret;
 }
 
 static int