drm: Tighten locking in drm_mode_getconnector

- Modeset state needs mode_config->connection mutex, that covers
  figuring out the encoder, and reading properties (since in the
  atomic case those need to look at connector->state).

- Don't hold any locks for stuff that's invariant (i.e. possible
  connectors).

- Same for connector lookup and unref, those don't need any locks.

- And finally the probe stuff is only protected by mode_config->mutex.

While at it updated the kerneldoc for these fields in drm_connector
and add docs explaining what's protected by which locks.

Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161213230814.19598-10-daniel.vetter@ffwll.ch

drivers/gpu/drm/drm_connector.c

@@ -1163,43 +1163,65 @@ int drm_mode_getconnector(struct drm_device *dev, void *data,
 
 	memset(&u_mode, 0, sizeof(struct drm_mode_modeinfo));
 
-	mutex_lock(&dev->mode_config.mutex);
-
 	connector = drm_connector_lookup(dev, out_resp->connector_id);
-	if (!connector) {
-		ret = -ENOENT;
-		goto out_unlock;
-	}
+	if (!connector)
+		return -ENOENT;
+
+	drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
+	encoder = drm_connector_get_encoder(connector);
+	if (encoder)
+		out_resp->encoder_id = encoder->base.id;
+	else
+		out_resp->encoder_id = 0;
+
+	ret = drm_mode_object_get_properties(&connector->base, file_priv->atomic,
+			(uint32_t __user *)(unsigned long)(out_resp->props_ptr),
+			(uint64_t __user *)(unsigned long)(out_resp->prop_values_ptr),
+			&out_resp->count_props);
+	drm_modeset_unlock(&dev->mode_config.connection_mutex);
+	if (ret)
+		goto out_unref;
 
 	for (i = 0; i < DRM_CONNECTOR_MAX_ENCODER; i++)
 		if (connector->encoder_ids[i] != 0)
 			encoders_count++;
 
+	if ((out_resp->count_encoders >= encoders_count) && encoders_count) {
+		copied = 0;
+		encoder_ptr = (uint32_t __user *)(unsigned long)(out_resp->encoders_ptr);
+		for (i = 0; i < DRM_CONNECTOR_MAX_ENCODER; i++) {
+			if (connector->encoder_ids[i] != 0) {
+				if (put_user(connector->encoder_ids[i],
+					     encoder_ptr + copied)) {
+					ret = -EFAULT;
+					goto out_unref;
+				}
+				copied++;
+			}
+		}
+	}
+	out_resp->count_encoders = encoders_count;
+
+	out_resp->connector_id = connector->base.id;
+	out_resp->connector_type = connector->connector_type;
+	out_resp->connector_type_id = connector->connector_type_id;
+
+	mutex_lock(&dev->mode_config.mutex);
 	if (out_resp->count_modes == 0) {
 		connector->funcs->fill_modes(connector,
 					     dev->mode_config.max_width,
 					     dev->mode_config.max_height);
 	}
 
-	/* delayed so we get modes regardless of pre-fill_modes state */
-	list_for_each_entry(mode, &connector->modes, head)
-		if (drm_mode_expose_to_userspace(mode, file_priv))
-			mode_count++;
-
-	out_resp->connector_id = connector->base.id;
-	out_resp->connector_type = connector->connector_type;
-	out_resp->connector_type_id = connector->connector_type_id;
 	out_resp->mm_width = connector->display_info.width_mm;
 	out_resp->mm_height = connector->display_info.height_mm;
 	out_resp->subpixel = connector->display_info.subpixel_order;
 	out_resp->connection = connector->status;
 
-	drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
-	encoder = drm_connector_get_encoder(connector);
-	if (encoder)
-		out_resp->encoder_id = encoder->base.id;
-	else
-		out_resp->encoder_id = 0;
+	/* delayed so we get modes regardless of pre-fill_modes state */
+	list_for_each_entry(mode, &connector->modes, head)
+		if (drm_mode_expose_to_userspace(mode, file_priv))
+			mode_count++;
 
 	/*
 	 * This ioctl is called twice, once to determine how much space is
@@ -1222,36 +1244,10 @@ int drm_mode_getconnector(struct drm_device *dev, void *data,
 		}
 	}
 	out_resp->count_modes = mode_count;
-
-	ret = drm_mode_object_get_properties(&connector->base, file_priv->atomic,
-			(uint32_t __user *)(unsigned long)(out_resp->props_ptr),
-			(uint64_t __user *)(unsigned long)(out_resp->prop_values_ptr),
-			&out_resp->count_props);
-	if (ret)
-		goto out;
-
-	if ((out_resp->count_encoders >= encoders_count) && encoders_count) {
-		copied = 0;
-		encoder_ptr = (uint32_t __user *)(unsigned long)(out_resp->encoders_ptr);
-		for (i = 0; i < DRM_CONNECTOR_MAX_ENCODER; i++) {
-			if (connector->encoder_ids[i] != 0) {
-				if (put_user(connector->encoder_ids[i],
-					     encoder_ptr + copied)) {
-					ret = -EFAULT;
-					goto out;
-				}
-				copied++;
-			}
-		}
-	}
-	out_resp->count_encoders = encoders_count;
-
 out:
-	drm_modeset_unlock(&dev->mode_config.connection_mutex);
-
-	drm_connector_unreference(connector);
-out_unlock:
 	mutex_unlock(&dev->mode_config.mutex);
+out_unref:
+	drm_connector_unreference(connector);
 
 	return ret;
 }

include/drm/drm_connector.h

@@ -563,9 +563,6 @@ struct drm_cmdline_mode {
  * @interlace_allowed: can this connector handle interlaced modes?
  * @doublescan_allowed: can this connector handle doublescan?
  * @stereo_allowed: can this connector handle stereo modes?
- * @modes: modes available on this connector (from fill_modes() + user)
- * @status: one of the drm_connector_status enums (connected, not, or unknown)
- * @probed_modes: list of modes derived directly from the display
  * @funcs: connector control functions
  * @edid_blob_ptr: DRM property containing EDID if present
  * @properties: property tracking for this connector
@@ -635,11 +632,27 @@ struct drm_connector {
 	 * Protected by @mutex.
 	 */
 	bool registered;
+
+	/**
+	 * @modes:
+	 * Modes available on this connector (from fill_modes() + user).
+	 * Protected by dev->mode_config.mutex.
+	 */
 	struct list_head modes; /* list of modes on this connector */
 
+	/**
+	 * @status:
+	 * One of the drm_connector_status enums (connected, not, or unknown).
+	 * Protected by dev->mode_config.mutex.
+	 */
 	enum drm_connector_status status;
 
-	/* these are modes added by probing with DDC or the BIOS */
+	/**
+	 * @probed_modes:
+	 * These are modes added by probing with DDC or the BIOS, before
+	 * filtering is applied. Used by the probe helpers.Protected by
+	 * dev->mode_config.mutex.
+	 */
 	struct list_head probed_modes;
 
 	/**
@@ -648,6 +661,8 @@ struct drm_connector {
 	 * flat panels in embedded systems, the driver should initialize the
 	 * display_info.width_mm and display_info.height_mm fields with the
 	 * physical size of the display.
+	 *
+	 * Protected by dev->mode_config.mutex.
 	 */
 	struct drm_display_info display_info;
 	const struct drm_connector_funcs *funcs;