[Intel-gfx] [PATCH] drm: Fix getconnector connection_mutex locking

[Rob Clark]

On Thu, Jun 5, 2014 at 5:12 AM, Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
> 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 at 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 at gmail.com>
> Cc: Dave Airlie <airlied at redhat.com>
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Reported-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>

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


> ---
>  drivers/gpu/drm/drm_crtc.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
> index b8cc4fe0a0f7..fe94cc10cd35 100644
> --- 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;
> --
> 2.0.0
>