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

[Rob Clark]

On Sun, Feb 22, 2015 at 5:38 AM, Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
> 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>

Reviewed-by: Rob Clark <robdclark at gmail.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
>