[Intel-gfx] [PATCH] drm: Fix deadlock due to getconnector locking changes

[Daniel Vetter]

In

daniel at phenom:~/linux/src$ git show ccfc08655
commit ccfc08655d5fd5076828f45fb09194c070f2f63a
Author: Rob Clark <robdclark at gmail.com>
Date:   Thu Dec 18 16:01:48 2014 -0500

    drm: tweak getconnector locking

We need to extend the locking to cover connector->state reading for
atomic drivers, but the above commit was a bit too eager and also
included the fill_modes callback. Which on i915 on old platforms using
load detection needs to acquire modeset locks, resulting in a deadlock
on output probing.

Reported-by: Marc Finet <m.dreadlock at gmail.com>
Cc: Marc Finet <m.dreadlock at gmail.com>
Cc: robdclark at gmail.com
Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
---
 drivers/gpu/drm/drm_crtc.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
index b15d720eda4c..ce5f1193ecd6 100644
--- a/drivers/gpu/drm/drm_crtc.c
+++ b/drivers/gpu/drm/drm_crtc.c
@@ -2180,7 +2180,6 @@ int drm_mode_getconnector(struct drm_device *dev, void *data,
 	DRM_DEBUG_KMS("[CONNECTOR:%d:?]\n", out_resp->connector_id);
 
 	mutex_lock(&dev->mode_config.mutex);
-	drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
 
 	connector = drm_connector_find(dev, out_resp->connector_id);
 	if (!connector) {
@@ -2210,6 +2209,8 @@ int drm_mode_getconnector(struct drm_device *dev, void *data,
 	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;
-- 
2.1.4