drm/atomic: Don't overrun the connector array when hotplugging

Yet another fallout from not considering DP MST hotplug. With the
previous patches we have stable indices, but it might still happen
that a connector gets added between when we allocate the array and
when we actually add a connector. Especially when we back off due to
ww mutex contention or similar issues.

So store the sizes of the arrays in struct drm_atomic_state and double
check them. We don't really care about races except that we want to
use a consistent value, so ACCESS_ONCE is all we need. And if we
indeed notice that we'd overrun the array then just give up and
restart the entire ioctl.

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

@@ -56,6 +56,8 @@ drm_atomic_state_alloc(struct drm_device *dev)
 	if (!state)
 		return NULL;
 
+	state->num_connector = ACCESS_ONCE(dev->mode_config.num_connector);
+
 	state->crtcs = kcalloc(dev->mode_config.num_crtc,
 			       sizeof(*state->crtcs), GFP_KERNEL);
 	if (!state->crtcs)
@@ -72,12 +74,12 @@ drm_atomic_state_alloc(struct drm_device *dev)
 				      sizeof(*state->plane_states), GFP_KERNEL);
 	if (!state->plane_states)
 		goto fail;
-	state->connectors = kcalloc(dev->mode_config.num_connector,
+	state->connectors = kcalloc(state->num_connector,
 				    sizeof(*state->connectors),
 				    GFP_KERNEL);
 	if (!state->connectors)
 		goto fail;
-	state->connector_states = kcalloc(dev->mode_config.num_connector,
+	state->connector_states = kcalloc(state->num_connector,
 					  sizeof(*state->connector_states),
 					  GFP_KERNEL);
 	if (!state->connector_states)
@@ -117,7 +119,7 @@ void drm_atomic_state_clear(struct drm_atomic_state *state)
 
 	DRM_DEBUG_KMS("Clearing atomic state %p\n", state);
 
-	for (i = 0; i < config->num_connector; i++) {
+	for (i = 0; i < state->num_connector; i++) {
 		struct drm_connector *connector = state->connectors[i];
 
 		if (!connector)
@@ -304,6 +306,21 @@ drm_atomic_get_connector_state(struct drm_atomic_state *state,
 
 	index = drm_connector_index(connector);
 
+	/*
+	 * Construction of atomic state updates can race with a connector
+	 * hot-add which might overflow. In this case flip the table and just
+	 * restart the entire ioctl - no one is fast enough to livelock a cpu
+	 * with physical hotplug events anyway.
+	 *
+	 * Note that we only grab the indexes once we have the right lock to
+	 * prevent hotplug/unplugging of connectors. So removal is no problem,
+	 * at most the array is a bit too large.
+	 */
+	if (index >= state->num_connector) {
+		DRM_DEBUG_KMS("Hot-added connector would overflow state array, restarting\n");
+		return -EAGAIN;
+	}
+
 	if (state->connector_states[index])
 		return state->connector_states[index];
 
@@ -499,10 +516,9 @@ int
 drm_atomic_connectors_for_crtc(struct drm_atomic_state *state,
 			       struct drm_crtc *crtc)
 {
-	int nconnectors = state->dev->mode_config.num_connector;
 	int i, num_connected_connectors = 0;
 
-	for (i = 0; i < nconnectors; i++) {
+	for (i = 0; i < state->num_connector; i++) {
 		struct drm_connector_state *conn_state;
 
 		conn_state = state->connector_states[i];

drivers/gpu/drm/drm_atomic_helper.c

@@ -249,7 +249,6 @@ static int
 mode_fixup(struct drm_atomic_state *state)
 {
 	int ncrtcs = state->dev->mode_config.num_crtc;
-	int nconnectors = state->dev->mode_config.num_connector;
 	struct drm_crtc_state *crtc_state;
 	struct drm_connector_state *conn_state;
 	int i;
@@ -264,7 +263,7 @@ mode_fixup(struct drm_atomic_state *state)
 		drm_mode_copy(&crtc_state->adjusted_mode, &crtc_state->mode);
 	}
 
-	for (i = 0; i < nconnectors; i++) {
+	for (i = 0; i < state->num_connector; i++) {
 		struct drm_encoder_helper_funcs *funcs;
 		struct drm_encoder *encoder;
 
@@ -336,7 +335,6 @@ drm_atomic_helper_check_prepare(struct drm_device *dev,
 				struct drm_atomic_state *state)
 {
 	int ncrtcs = dev->mode_config.num_crtc;
-	int nconnectors = dev->mode_config.num_connector;
 	struct drm_crtc *crtc;
 	struct drm_crtc_state *crtc_state;
 	int i, ret;
@@ -361,7 +359,7 @@ drm_atomic_helper_check_prepare(struct drm_device *dev,
 		}
 	}
 
-	for (i = 0; i < nconnectors; i++) {
+	for (i = 0; i < state->num_connector; i++) {
 		/*
 		 * This only sets crtc->mode_changed for routing changes,
 		 * drivers must set crtc->mode_changed themselves when connector
@@ -485,10 +483,9 @@ static void
 disable_outputs(struct drm_device *dev, struct drm_atomic_state *old_state)
 {
 	int ncrtcs = old_state->dev->mode_config.num_crtc;
-	int nconnectors = old_state->dev->mode_config.num_connector;
 	int i;
 
-	for (i = 0; i < nconnectors; i++) {
+	for (i = 0; i < old_state->num_connector; i++) {
 		struct drm_connector_state *old_conn_state;
 		struct drm_connector *connector;
 		struct drm_encoder_helper_funcs *funcs;
@@ -553,12 +550,11 @@ disable_outputs(struct drm_device *dev, struct drm_atomic_state *old_state)
 static void
 set_routing_links(struct drm_device *dev, struct drm_atomic_state *old_state)
 {
-	int nconnectors = dev->mode_config.num_connector;
 	int ncrtcs = old_state->dev->mode_config.num_crtc;
 	int i;
 
 	/* clear out existing links */
-	for (i = 0; i < nconnectors; i++) {
+	for (i = 0; i < old_state->num_connector; i++) {
 		struct drm_connector *connector;
 
 		connector = old_state->connectors[i];
@@ -573,7 +569,7 @@ set_routing_links(struct drm_device *dev, struct drm_atomic_state *old_state)
 	}
 
 	/* set new links */
-	for (i = 0; i < nconnectors; i++) {
+	for (i = 0; i < old_state->num_connector; i++) {
 		struct drm_connector *connector;
 
 		connector = old_state->connectors[i];
@@ -608,7 +604,6 @@ static void
 crtc_set_mode(struct drm_device *dev, struct drm_atomic_state *old_state)
 {
 	int ncrtcs = old_state->dev->mode_config.num_crtc;
-	int nconnectors = old_state->dev->mode_config.num_connector;
 	int i;
 
 	for (i = 0; i < ncrtcs; i++) {
@@ -626,7 +621,7 @@ crtc_set_mode(struct drm_device *dev, struct drm_atomic_state *old_state)
 			funcs->mode_set_nofb(crtc);
 	}
 
-	for (i = 0; i < nconnectors; i++) {
+	for (i = 0; i < old_state->num_connector; i++) {
 		struct drm_connector *connector;
 		struct drm_crtc_state *new_crtc_state;
 		struct drm_encoder_helper_funcs *funcs;
@@ -687,7 +682,6 @@ void drm_atomic_helper_commit_post_planes(struct drm_device *dev,
 					  struct drm_atomic_state *old_state)
 {
 	int ncrtcs = old_state->dev->mode_config.num_crtc;
-	int nconnectors = old_state->dev->mode_config.num_connector;
 	int i;
 
 	for (i = 0; i < ncrtcs; i++) {
@@ -706,7 +700,7 @@ void drm_atomic_helper_commit_post_planes(struct drm_device *dev,
 			funcs->commit(crtc);
 	}
 
-	for (i = 0; i < nconnectors; i++) {
+	for (i = 0; i < old_state->num_connector; i++) {
 		struct drm_connector *connector;
 		struct drm_encoder_helper_funcs *funcs;
 		struct drm_encoder *encoder;
@@ -1304,7 +1298,6 @@ static int update_output_state(struct drm_atomic_state *state,
 {
 	struct drm_device *dev = set->crtc->dev;
 	struct drm_connector_state *conn_state;
-	int nconnectors = state->dev->mode_config.num_connector;
 	int ncrtcs = state->dev->mode_config.num_crtc;
 	int ret, i, j;
 
@@ -1333,7 +1326,7 @@ static int update_output_state(struct drm_atomic_state *state,
 	}
 
 	/* Then recompute connector->crtc links and crtc enabling state. */
-	for (i = 0; i < nconnectors; i++) {
+	for (i = 0; i < state->num_connector; i++) {
 		struct drm_connector *connector;
 
 		connector = state->connectors[i];

include/drm/drm_crtc.h

@@ -825,6 +825,7 @@ struct drm_bridge {
  * @plane_states: pointer to array of plane states pointers
  * @crtcs: pointer to array of CRTC pointers
  * @crtc_states: pointer to array of CRTC states pointers
+ * @num_connector: size of the @connectors and @connector_states arrays
  * @connectors: pointer to array of connector pointers
  * @connector_states: pointer to array of connector states pointers
  * @acquire_ctx: acquire context for this atomic modeset state update
@@ -836,6 +837,7 @@ struct drm_atomic_state {
 	struct drm_plane_state **plane_states;
 	struct drm_crtc **crtcs;
 	struct drm_crtc_state **crtc_states;
+	int num_connector;
 	struct drm_connector **connectors;
 	struct drm_connector_state **connector_states;