drm/fb-helper: Fix locking in drm_fb_helper_hotplug_event

Driver's and ->fill_modes functions are allowed to grab crtc mutexes
(for e.g. load detect). Hence we need to first only grab the general
kms mutex, and only in a second step grab all locks to do the
modesets.

This prevents a deadlock on my gm45 in the tv load detect code called
by drm_helper_probe_single_connector_modes.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 5 insertions, 3 deletions

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index 59d6b9bf204b..892ff9f95975 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -1544,10 +1544,10 @@ int drm_fb_helper_hotplug_event(struct drm_fb_helper *fb_helper)
         if (!fb_helper->fb)
                 return 0;
 
-        drm_modeset_lock_all(dev);
+        mutex_lock(&fb_helper->dev->mode_config.mutex);
         if (!drm_fb_helper_is_bound(fb_helper)) {
                 fb_helper->delayed_hotplug = true;
-                drm_modeset_unlock_all(dev);
+                mutex_unlock(&fb_helper->dev->mode_config.mutex);
                 return 0;
         }
         DRM_DEBUG_KMS("\n");
@@ -1558,9 +1558,11 @@ int drm_fb_helper_hotplug_event(struct drm_fb_helper *fb_helper)
 
         count = drm_fb_helper_probe_connector_modes(fb_helper, max_width,
                                                     max_height);
+        mutex_unlock(&fb_helper->dev->mode_config.mutex);
+
+        drm_modeset_lock_all(dev);
         drm_setup_crtcs(fb_helper);
         drm_modeset_unlock_all(dev);
-
         drm_fb_helper_set_par(fb_helper->fbdev);
 
         return 0;