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

Daniel Vetter
2020-06-03T08:24:19Z

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@codeaurora.org>
> Signed-off-by: Steve Cohen <cohens@codeaurora.org>

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");
> --
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project
>
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--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

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