drm: Fix getconnector connection_mutex locking

I've fumbled my own idea and enthusiastically wrapped all the
getconnector code with the connection_mutex. But we only need it to
chase the connector->encoder link. Even there it's not really needed
since races with userspace won't matter, but better paranoid and
consistent about this stuff.

If we grap it everywhere connector probe callbacks can't grab it
themselves, which means they'll deadlock. i915 does that for the load
detect pipe. Furthermore i915 needs to do a ww dance since we also
need to grab the mutex of the load detect crtc.

This is a regression from

commit 6e9f798d91c526982cca0026cd451e8fdbf18aaf
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Thu May 29 23:54:47 2014 +0200

    drm: Split connection_mutex out of mode_config.mutex (v3)

Cc: Rob Clark <robdclark@gmail.com>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reported-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
index 43735f38cd17fd4c7eb6dc7851d8508f4c668bba..239342f554b4d9dd4dab156331bf6d09be9b9671 100644 (file)
--- a/drivers/gpu/drm/drm_crtc.c
+++ b/drivers/gpu/drm/drm_crtc.c
@@ -1838,7 +1838,6 @@ 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) {
@@ -1872,10 +1871,12 @@ 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);
        if (connector->encoder)
                out_resp->encoder_id = connector->encoder->base.id;
        else
                out_resp->encoder_id = 0;
+       drm_modeset_unlock(&dev->mode_config.connection_mutex);
 
        /*
         * This ioctl is called twice, once to determine how much space is
@@ -1937,7 +1938,6 @@ int drm_mode_getconnector(struct drm_device *dev, void *data,
        out_resp->count_encoders = encoders_count;
 
 out:
-       drm_modeset_unlock(&dev->mode_config.connection_mutex);
        mutex_unlock(&dev->mode_config.mutex);
 
        return ret;