Re: [PATCH 2/2] drm/connector: send hotplug uevent on connector cleanup

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Mon, Oct 17, 2022 at 03:32:01PM +0000, Simon Ser wrote:
> A typical DP-MST unplug removes a KMS connector. However care must
> be taken to properly synchronize with user-space. The expected
> sequence of events is the following:
> 
> 1. The kernel notices that the DP-MST port is gone.
> 2. The kernel marks the connector as disconnected, then sends a
>    uevent to make user-space re-scan the connector list.
> 3. User-space notices the connector goes from connected to disconnected,
>    disables it.
> 4. Kernel handles the the IOCTL disabling the connector. On success,
>    the very last reference to the struct drm_connector is dropped and
>    drm_connector_cleanup() is called.
> 5. The connector is removed from the list, and a uevent is sent to tell
>    user-space that the connector disappeared.
> 
> The very last step was missing. As a result, user-space thought the
> connector still existed and could try to disable it again. Since the
> kernel no longer knows about the connector, that would end up with
> EINVAL and confused user-space.

So is the uevent sent by the mst delayed destroy work
useless now, or what is going on there?

> 
> Fix this by sending a hotplug uevent from drm_connector_cleanup().
> 
> Signed-off-by: Simon Ser <contact@emersion.fr>
> Cc: stable@vger.kernel.org
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Lyude Paul <lyude@redhat.com>
> Cc: Jonas Ådahl <jadahl@redhat.com>
> ---
>  drivers/gpu/drm/drm_connector.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
> index e3142c8142b3..90dad87e9ad0 100644
> --- a/drivers/gpu/drm/drm_connector.c
> +++ b/drivers/gpu/drm/drm_connector.c
> @@ -582,6 +582,9 @@ void drm_connector_cleanup(struct drm_connector *connector)
>  	mutex_destroy(&connector->mutex);
>  
>  	memset(connector, 0, sizeof(*connector));
> +
> +	if (dev->registered)
> +		drm_sysfs_hotplug_event(dev);
>  }
>  EXPORT_SYMBOL(drm_connector_cleanup);
>  
> -- 
> 2.38.0
> 

-- 
Ville Syrjälä
Intel