drm/atomic: Only destroy connector states with connection mutex held

Otherwise the connector might have been unplugged and destroyed while
we didn't look. Yet another fallout from DP MST hotplugging that I
didn't consider.

To make sure we get this right add an appropriate WARN_ON to
drm_atomic_state_clear (obviously only when we actually have a state
to clear up). And reorder all the state_clear and backoff calls to
make it work out properly.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Reviewed-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_atomic.c

@@ -112,21 +112,24 @@ EXPORT_SYMBOL(drm_atomic_state_alloc);
 void drm_atomic_state_clear(struct drm_atomic_state *state)
 {
 	struct drm_device *dev = state->dev;
+	struct drm_mode_config *config = &dev->mode_config;
 	int i;
 
 	DRM_DEBUG_KMS("Clearing atomic state %p\n", state);
 
-	for (i = 0; i < dev->mode_config.num_connector; i++) {
+	for (i = 0; i < config->num_connector; i++) {
 		struct drm_connector *connector = state->connectors[i];
 
 		if (!connector)
 			continue;
 
+		WARN_ON(!drm_modeset_is_locked(&config->connection_mutex));
+
 		connector->funcs->atomic_destroy_state(connector,
 						       state->connector_states[i]);
 	}
 
-	for (i = 0; i < dev->mode_config.num_crtc; i++) {
+	for (i = 0; i < config->num_crtc; i++) {
 		struct drm_crtc *crtc = state->crtcs[i];
 
 		if (!crtc)
@@ -136,7 +139,7 @@ void drm_atomic_state_clear(struct drm_atomic_state *state)
 						  state->crtc_states[i]);
 	}
 
-	for (i = 0; i < dev->mode_config.num_total_plane; i++) {
+	for (i = 0; i < config->num_total_plane; i++) {
 		struct drm_plane *plane = state->planes[i];
 
 		if (!plane)

drivers/gpu/drm/drm_atomic_helper.c

@@ -1217,8 +1217,8 @@ fail:
 
 	return ret;
 backoff:
-	drm_atomic_legacy_backoff(state);
 	drm_atomic_state_clear(state);
+	drm_atomic_legacy_backoff(state);
 
 	/*
 	 * Someone might have exchanged the framebuffer while we dropped locks
@@ -1285,8 +1285,8 @@ fail:
 
 	return ret;
 backoff:
-	drm_atomic_legacy_backoff(state);
 	drm_atomic_state_clear(state);
+	drm_atomic_legacy_backoff(state);
 
 	/*
 	 * Someone might have exchanged the framebuffer while we dropped locks
@@ -1462,8 +1462,8 @@ fail:
 
 	return ret;
 backoff:
-	drm_atomic_legacy_backoff(state);
 	drm_atomic_state_clear(state);
+	drm_atomic_legacy_backoff(state);
 
 	/*
 	 * Someone might have exchanged the framebuffer while we dropped locks
@@ -1528,8 +1528,8 @@ fail:
 
 	return ret;
 backoff:
-	drm_atomic_legacy_backoff(state);
 	drm_atomic_state_clear(state);
+	drm_atomic_legacy_backoff(state);
 
 	goto retry;
 }
@@ -1587,8 +1587,8 @@ fail:
 
 	return ret;
 backoff:
-	drm_atomic_legacy_backoff(state);
 	drm_atomic_state_clear(state);
+	drm_atomic_legacy_backoff(state);
 
 	goto retry;
 }
@@ -1646,8 +1646,8 @@ fail:
 
 	return ret;
 backoff:
-	drm_atomic_legacy_backoff(state);
 	drm_atomic_state_clear(state);
+	drm_atomic_legacy_backoff(state);
 
 	goto retry;
 }
@@ -1725,8 +1725,8 @@ fail:
 
 	return ret;
 backoff:
-	drm_atomic_legacy_backoff(state);
 	drm_atomic_state_clear(state);
+	drm_atomic_legacy_backoff(state);
 
 	/*
 	 * Someone might have exchanged the framebuffer while we dropped locks