drm/i915: Do interrupible mutex lock first to avoid locking for unreference

One of the primarily consumers of the i915 driver is X, a large signal
driven application. Frequently when writing into the buffers, there is a
pending signal which causes us not to take the interruptible lock but
then we need to take that same lock around the object unreference. By
rearranging the code to do the interruptible lock as the first check, we
can avoid the frequent additional locking around the unreference.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/i915_gem.c

@@ -547,16 +547,16 @@ i915_gem_pread_ioctl(struct drm_device *dev, void *data,
 	struct drm_i915_gem_object *obj_priv;
 	int ret = 0;
 
-	obj = drm_gem_object_lookup(dev, file_priv, args->handle);
-	if (obj == NULL)
-		return -ENOENT;
-	obj_priv = to_intel_bo(obj);
-
 	ret = i915_mutex_lock_interruptible(dev);
-	if (ret) {
-		drm_gem_object_unreference_unlocked(obj);
+	if (ret)
 		return ret;
+
+	obj = drm_gem_object_lookup(dev, file_priv, args->handle);
+	if (obj == NULL) {
+		ret = -ENOENT;
+		goto unlock;
 	}
+	obj_priv = to_intel_bo(obj);
 
 	/* Bounds check source.  */
 	if (args->offset > obj->size || args->size > obj->size - args->offset) {
@@ -601,6 +601,7 @@ out_put:
 	i915_gem_object_put_pages(obj);
 out:
 	drm_gem_object_unreference(obj);
+unlock:
 	mutex_unlock(&dev->struct_mutex);
 	return ret;
 }
@@ -982,16 +983,17 @@ i915_gem_pwrite_ioctl(struct drm_device *dev, void *data,
 	struct drm_i915_gem_object *obj_priv;
 	int ret = 0;
 
-	obj = drm_gem_object_lookup(dev, file, args->handle);
-	if (obj == NULL)
-		return -ENOENT;
-	obj_priv = to_intel_bo(obj);
-
 	ret = i915_mutex_lock_interruptible(dev);
-	if (ret) {
-		drm_gem_object_unreference_unlocked(obj);
+	if (ret)
 		return ret;
+
+	obj = drm_gem_object_lookup(dev, file, args->handle);
+	if (obj == NULL) {
+		ret = -ENOENT;
+		goto unlock;
 	}
+	obj_priv = to_intel_bo(obj);
+
 
 	/* Bounds check destination. */
 	if (args->offset > obj->size || args->size > obj->size - args->offset) {
@@ -1062,6 +1064,7 @@ out_put:
 
 out:
 	drm_gem_object_unreference(obj);
+unlock:
 	mutex_unlock(&dev->struct_mutex);
 	return ret;
 }
@@ -1098,16 +1101,16 @@ i915_gem_set_domain_ioctl(struct drm_device *dev, void *data,
 	if (write_domain != 0 && read_domains != write_domain)
 		return -EINVAL;
 
-	obj = drm_gem_object_lookup(dev, file_priv, args->handle);
-	if (obj == NULL)
-		return -ENOENT;
-	obj_priv = to_intel_bo(obj);
-
 	ret = i915_mutex_lock_interruptible(dev);
-	if (ret) {
-		drm_gem_object_unreference_unlocked(obj);
+	if (ret)
 		return ret;
+
+	obj = drm_gem_object_lookup(dev, file_priv, args->handle);
+	if (obj == NULL) {
+		ret = -ENOENT;
+		goto unlock;
 	}
+	obj_priv = to_intel_bo(obj);
 
 	intel_mark_busy(dev, obj);
 
@@ -1139,6 +1142,7 @@ i915_gem_set_domain_ioctl(struct drm_device *dev, void *data,
 		list_move_tail(&obj_priv->list, &dev_priv->mm.inactive_list);
 
 	drm_gem_object_unreference(obj);
+unlock:
 	mutex_unlock(&dev->struct_mutex);
 	return ret;
 }
@@ -1157,14 +1161,14 @@ i915_gem_sw_finish_ioctl(struct drm_device *dev, void *data,
 	if (!(dev->driver->driver_features & DRIVER_GEM))
 		return -ENODEV;
 
-	obj = drm_gem_object_lookup(dev, file_priv, args->handle);
-	if (obj == NULL)
-		return -ENOENT;
-
 	ret = i915_mutex_lock_interruptible(dev);
-	if (ret) {
-		drm_gem_object_unreference_unlocked(obj);
+	if (ret)
 		return ret;
+
+	obj = drm_gem_object_lookup(dev, file_priv, args->handle);
+	if (obj == NULL) {
+		ret = -ENOENT;
+		goto unlock;
 	}
 
 	/* Pinned buffers may be scanout, so flush the cache */
@@ -1172,6 +1176,7 @@ i915_gem_sw_finish_ioctl(struct drm_device *dev, void *data,
 		i915_gem_object_flush_cpu_write_domain(obj);
 
 	drm_gem_object_unreference(obj);
+unlock:
 	mutex_unlock(&dev->struct_mutex);
 	return ret;
 }
@@ -1469,33 +1474,27 @@ i915_gem_mmap_gtt_ioctl(struct drm_device *dev, void *data,
 	if (!(dev->driver->driver_features & DRIVER_GEM))
 		return -ENODEV;
 
-	obj = drm_gem_object_lookup(dev, file_priv, args->handle);
-	if (obj == NULL)
-		return -ENOENT;
-
 	ret = i915_mutex_lock_interruptible(dev);
-	if (ret) {
-		drm_gem_object_unreference_unlocked(obj);
+	if (ret)
 		return ret;
-	}
 
+	obj = drm_gem_object_lookup(dev, file_priv, args->handle);
+	if (obj == NULL) {
+		ret = -ENOENT;
+		goto unlock;
+	}
 	obj_priv = to_intel_bo(obj);
 
 	if (obj_priv->madv != I915_MADV_WILLNEED) {
 		DRM_ERROR("Attempting to mmap a purgeable buffer\n");
-		drm_gem_object_unreference(obj);
-		mutex_unlock(&dev->struct_mutex);
-		return -EINVAL;
+		ret = -EINVAL;
+		goto out;
 	}
 
-
 	if (!obj_priv->mmap_offset) {
 		ret = i915_gem_create_mmap_offset(obj);
-		if (ret) {
-			drm_gem_object_unreference(obj);
-			mutex_unlock(&dev->struct_mutex);
-			return ret;
-		}
+		if (ret)
+			goto out;
 	}
 
 	args->offset = obj_priv->mmap_offset;
@@ -1506,17 +1505,15 @@ i915_gem_mmap_gtt_ioctl(struct drm_device *dev, void *data,
 	 */
 	if (!obj_priv->agp_mem) {
 		ret = i915_gem_object_bind_to_gtt(obj, 0);
-		if (ret) {
-			drm_gem_object_unreference(obj);
-			mutex_unlock(&dev->struct_mutex);
-			return ret;
-		}
+		if (ret)
+			goto out;
 	}
 
+out:
 	drm_gem_object_unreference(obj);
+unlock:
 	mutex_unlock(&dev->struct_mutex);
-
-	return 0;
+	return ret;
 }
 
 static void
@@ -4100,44 +4097,36 @@ i915_gem_pin_ioctl(struct drm_device *dev, void *data,
 	struct drm_i915_gem_object *obj_priv;
 	int ret;
 
+	ret = i915_mutex_lock_interruptible(dev);
+	if (ret)
+		return ret;
+
 	obj = drm_gem_object_lookup(dev, file_priv, args->handle);
 	if (obj == NULL) {
-		DRM_ERROR("Bad handle in i915_gem_pin_ioctl(): %d\n",
-			  args->handle);
-		return -ENOENT;
+		ret = -ENOENT;
+		goto unlock;
 	}
 	obj_priv = to_intel_bo(obj);
 
-	ret = i915_mutex_lock_interruptible(dev);
-	if (ret) {
-		drm_gem_object_unreference_unlocked(obj);
-		return ret;
-	}
-
 	if (obj_priv->madv != I915_MADV_WILLNEED) {
 		DRM_ERROR("Attempting to pin a purgeable buffer\n");
-		drm_gem_object_unreference(obj);
-		mutex_unlock(&dev->struct_mutex);
-		return -EINVAL;
+		ret = -EINVAL;
+		goto out;
 	}
 
 	if (obj_priv->pin_filp != NULL && obj_priv->pin_filp != file_priv) {
 		DRM_ERROR("Already pinned in i915_gem_pin_ioctl(): %d\n",
 			  args->handle);
-		drm_gem_object_unreference(obj);
-		mutex_unlock(&dev->struct_mutex);
-		return -EINVAL;
+		ret = -EINVAL;
+		goto out;
 	}
 
 	obj_priv->user_pin_count++;
 	obj_priv->pin_filp = file_priv;
 	if (obj_priv->user_pin_count == 1) {
 		ret = i915_gem_object_pin(obj, args->alignment);
-		if (ret != 0) {
-			drm_gem_object_unreference(obj);
-			mutex_unlock(&dev->struct_mutex);
-			return ret;
-		}
+		if (ret)
+			goto out;
 	}
 
 	/* XXX - flush the CPU caches for pinned objects
@@ -4145,10 +4134,11 @@ i915_gem_pin_ioctl(struct drm_device *dev, void *data,
 	 */
 	i915_gem_object_flush_cpu_write_domain(obj);
 	args->offset = obj_priv->gtt_offset;
+out:
 	drm_gem_object_unreference(obj);
+unlock:
 	mutex_unlock(&dev->struct_mutex);
-
-	return 0;
+	return ret;
 }
 
 int
@@ -4160,27 +4150,22 @@ i915_gem_unpin_ioctl(struct drm_device *dev, void *data,
 	struct drm_i915_gem_object *obj_priv;
 	int ret;
 
+	ret = i915_mutex_lock_interruptible(dev);
+	if (ret)
+		return ret;
+
 	obj = drm_gem_object_lookup(dev, file_priv, args->handle);
 	if (obj == NULL) {
-		DRM_ERROR("Bad handle in i915_gem_unpin_ioctl(): %d\n",
-			  args->handle);
-		return -ENOENT;
+		ret = -ENOENT;
+		goto unlock;
 	}
-
 	obj_priv = to_intel_bo(obj);
 
-	ret = i915_mutex_lock_interruptible(dev);
-	if (ret) {
-		drm_gem_object_unreference_unlocked(obj);
-		return ret;
-	}
-
 	if (obj_priv->pin_filp != file_priv) {
 		DRM_ERROR("Not pinned by caller in i915_gem_pin_ioctl(): %d\n",
 			  args->handle);
-		drm_gem_object_unreference(obj);
-		mutex_unlock(&dev->struct_mutex);
-		return -EINVAL;
+		ret = -EINVAL;
+		goto out;
 	}
 	obj_priv->user_pin_count--;
 	if (obj_priv->user_pin_count == 0) {
@@ -4188,9 +4173,11 @@ i915_gem_unpin_ioctl(struct drm_device *dev, void *data,
 		i915_gem_object_unpin(obj);
 	}
 
+out:
 	drm_gem_object_unreference(obj);
+unlock:
 	mutex_unlock(&dev->struct_mutex);
-	return 0;
+	return ret;
 }
 
 int
@@ -4202,25 +4189,22 @@ i915_gem_busy_ioctl(struct drm_device *dev, void *data,
 	struct drm_i915_gem_object *obj_priv;
 	int ret;
 
-	obj = drm_gem_object_lookup(dev, file_priv, args->handle);
-	if (obj == NULL) {
-		DRM_ERROR("Bad handle in i915_gem_busy_ioctl(): %d\n",
-			  args->handle);
-		return -ENOENT;
-	}
-
 	ret = i915_mutex_lock_interruptible(dev);
-	if (ret) {
-		drm_gem_object_unreference_unlocked(obj);
+	if (ret)
 		return ret;
+
+	obj = drm_gem_object_lookup(dev, file_priv, args->handle);
+	if (obj == NULL) {
+		ret = -ENOENT;
+		goto unlock;
 	}
+	obj_priv = to_intel_bo(obj);
 
 	/* Count all active objects as busy, even if they are currently not used
 	 * by the gpu. Users of this interface expect objects to eventually
 	 * become non-busy without any further actions, therefore emit any
 	 * necessary flushes here.
 	 */
-	obj_priv = to_intel_bo(obj);
 	args->busy = obj_priv->active;
 	if (args->busy) {
 		/* Unconditionally flush objects, even when the gpu still uses this
@@ -4244,8 +4228,9 @@ i915_gem_busy_ioctl(struct drm_device *dev, void *data,
 	}
 
 	drm_gem_object_unreference(obj);
+unlock:
 	mutex_unlock(&dev->struct_mutex);
-	return 0;
+	return ret;
 }
 
 int
@@ -4272,26 +4257,20 @@ i915_gem_madvise_ioctl(struct drm_device *dev, void *data,
 	    return -EINVAL;
 	}
 
+	ret = i915_mutex_lock_interruptible(dev);
+	if (ret)
+		return ret;
+
 	obj = drm_gem_object_lookup(dev, file_priv, args->handle);
 	if (obj == NULL) {
-		DRM_ERROR("Bad handle in i915_gem_madvise_ioctl(): %d\n",
-			  args->handle);
-		return -ENOENT;
+		ret = -ENOENT;
+		goto unlock;
 	}
 	obj_priv = to_intel_bo(obj);
 
-	ret = i915_mutex_lock_interruptible(dev);
-	if (ret) {
-		drm_gem_object_unreference_unlocked(obj);
-		return ret;
-	}
-
 	if (obj_priv->pin_count) {
-		drm_gem_object_unreference(obj);
-		mutex_unlock(&dev->struct_mutex);
-
-		DRM_ERROR("Attempted i915_gem_madvise_ioctl() on a pinned object\n");
-		return -EINVAL;
+		ret = -EINVAL;
+		goto out;
 	}
 
 	if (obj_priv->madv != __I915_MADV_PURGED)
@@ -4304,10 +4283,11 @@ i915_gem_madvise_ioctl(struct drm_device *dev, void *data,
 
 	args->retained = obj_priv->madv != __I915_MADV_PURGED;
 
+out:
 	drm_gem_object_unreference(obj);
+unlock:
 	mutex_unlock(&dev->struct_mutex);
-
-	return 0;
+	return ret;
 }
 
 struct drm_gem_object * i915_gem_alloc_object(struct drm_device *dev,