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

Jani Nikula
2015-02-23T08:52:51Z

On Sun, 22 Feb 2015, Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
> In
>
> daniel@phenom:~/linux/src$ git show ccfc08655

copy-paste fail?

J.

> commit ccfc08655d5fd5076828f45fb09194c070f2f63a
> Author: Rob Clark <robdclark@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@gmail.com>
> Cc: Marc Finet <m.dreadlock@gmail.com>
> Cc: robdclark@gmail.com
> Signed-off-by: Daniel Vetter <daniel.vetter@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
>
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--
Jani Nikula, Intel Open Source Technology Center