Re: [PATCH] drm/connector: notify userspace on hotplug after register complete

[Daniel Vetter]

On Tue, Jun 02, 2020 at 08:37:31PM -0700, Jeykumar Sankaran wrote:
> drm connector notifies userspace on hotplug event prematurely before
> late_register and mode_object register completes. This leads to a race
> between userspace and kernel on updating the IDR list. So, move the
> notification to end of connector register.
> 
> Signed-off-by: Jeykumar Sankaran <jsanka@xxxxxxxxxxxxxx>
> Signed-off-by: Steve Cohen <cohens@xxxxxxxxxxxxxx>

Hm on the unregister side we don't have the race, there we remove
everything and then send out the uevent. But there the uevent is also
generated in a separate step, so I wonder whether we shouldn't do the same
for register for symmetry ...

Anyway this looks good, nice catch, I'll add cc: stable and merge.
-Daniel

> ---
>  drivers/gpu/drm/drm_connector.c | 5 +++++
>  drivers/gpu/drm/drm_sysfs.c     | 3 ---
>  2 files changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
> index b1099e1..d877ddc 100644
> --- a/drivers/gpu/drm/drm_connector.c
> +++ b/drivers/gpu/drm/drm_connector.c
> @@ -27,6 +27,7 @@
>  #include <drm/drm_print.h>
>  #include <drm/drm_drv.h>
>  #include <drm/drm_file.h>
> +#include <drm/drm_sysfs.h>
>  
>  #include <linux/uaccess.h>
>  
> @@ -523,6 +524,10 @@ int drm_connector_register(struct drm_connector *connector)
>  	drm_mode_object_register(connector->dev, &connector->base);
>  
>  	connector->registration_state = DRM_CONNECTOR_REGISTERED;
> +
> +	/* Let userspace know we have a new connector */
> +	drm_sysfs_hotplug_event(connector->dev);
> +
>  	goto unlock;
>  
>  err_debugfs:
> diff --git a/drivers/gpu/drm/drm_sysfs.c b/drivers/gpu/drm/drm_sysfs.c
> index 939f003..f0336c8 100644
> --- a/drivers/gpu/drm/drm_sysfs.c
> +++ b/drivers/gpu/drm/drm_sysfs.c
> @@ -291,9 +291,6 @@ int drm_sysfs_connector_add(struct drm_connector *connector)
>  		return PTR_ERR(connector->kdev);
>  	}
>  
> -	/* Let userspace know we have a new connector */
> -	drm_sysfs_hotplug_event(dev);
> -
>  	if (connector->ddc)
>  		return sysfs_create_link(&connector->kdev->kobj,
>  				 &connector->ddc->dev.kobj, "ddc");
> -- 
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> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch