drm: prevent double-(un)registration for connectors

If we're unlucky then the registration from a hotplugged connector
might race with the final registration step on driver load. And since
MST topology discover is asynchronous that's even somewhat likely.

v2: Also update the kerneldoc for @registered!

v3: Review from Chris:
- Improve kerneldoc for late_register/early_unregister callbacks.
- Use mutex_destroy.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Reported-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161218133545.2106-1-daniel.vetter@ffwll.ch
(cherry picked from commit e73ab00e9a0f1731f34d0620a9c55f5c30c4ad4e)

1 files changed, 15 insertions, 5 deletions

diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
index 5a4526289392..8be60a4576b3 100644
--- a/drivers/gpu/drm/drm_connector.c
+++ b/drivers/gpu/drm/drm_connector.c
@@ -225,6 +225,7 @@ int drm_connector_init(struct drm_device *dev,
 
         INIT_LIST_HEAD(&connector->probed_modes);
         INIT_LIST_HEAD(&connector->modes);
+        mutex_init(&connector->mutex);
         connector->edid_blob_ptr = NULL;
         connector->status = connector_status_unknown;
 
@@ -359,6 +360,8 @@ void drm_connector_cleanup(struct drm_connector *connector)
                 connector->funcs->atomic_destroy_state(connector,
                                                        connector->state);
 
+        mutex_destroy(&connector->mutex);
+
         memset(connector, 0, sizeof(*connector));
 }
 EXPORT_SYMBOL(drm_connector_cleanup);
@@ -374,14 +377,15 @@ EXPORT_SYMBOL(drm_connector_cleanup);
  */
 int drm_connector_register(struct drm_connector *connector)
 {
-        int ret;
+        int ret = 0;
 
+        mutex_lock(&connector->mutex);
         if (connector->registered)
-                return 0;
+                goto unlock;
 
         ret = drm_sysfs_connector_add(connector);
         if (ret)
-                return ret;
+                goto unlock;
 
         ret = drm_debugfs_connector_add(connector);
         if (ret) {
@@ -397,12 +401,14 @@ int drm_connector_register(struct drm_connector *connector)
         drm_mode_object_register(connector->dev, &connector->base);
 
         connector->registered = true;
-        return 0;
+        goto unlock;
 
 err_debugfs:
         drm_debugfs_connector_remove(connector);
 err_sysfs:
         drm_sysfs_connector_remove(connector);
+unlock:
+        mutex_unlock(&connector->mutex);
         return ret;
 }
 EXPORT_SYMBOL(drm_connector_register);
@@ -415,8 +421,11 @@ EXPORT_SYMBOL(drm_connector_register);
  */
 void drm_connector_unregister(struct drm_connector *connector)
 {
-        if (!connector->registered)
+        mutex_lock(&connector->mutex);
+        if (!connector->registered) {
+                mutex_unlock(&connector->mutex);
                 return;
+        }
 
         if (connector->funcs->early_unregister)
                 connector->funcs->early_unregister(connector);
@@ -425,6 +434,7 @@ void drm_connector_unregister(struct drm_connector *connector)
         drm_debugfs_connector_remove(connector);
 
         connector->registered = false;
+        mutex_unlock(&connector->mutex);
 }
 EXPORT_SYMBOL(drm_connector_unregister);