Re: [PATCH 1/9] drm/connector: Make the drm_sysfs connector->kdev device hold a reference to the connector

From: Daniel Vetter <daniel@ffwll.ch>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Daniel Vetter <daniel@ffwll.ch>,
	Hans de Goede <hdegoede@redhat.com>,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	Maxime Ripard <mripard@kernel.org>,
	Thomas Zimmermann <tzimmermann@suse.de>,
	David Airlie <airlied@linux.ie>,
	Jani Nikula <jani.nikula@linux.intel.com>,
	Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
	Rodrigo Vivi <rodrigo.vivi@intel.com>,
	Guenter Roeck <linux@roeck-us.net>,
	Heikki Krogerus <heikki.krogerus@linux.intel.com>,
	intel-gfx <intel-gfx@lists.freedesktop.org>,
	dri-devel@lists.freedesktop.org,
	platform-driver-x86@vger.kernel.org, linux-usb@vger.kernel.org
Subject: Re: [PATCH 1/9] drm/connector: Make the drm_sysfs connector->kdev device hold a reference to the connector
Date: Thu, 29 Apr 2021 14:04:55 +0200	[thread overview]
Message-ID: <YIqg59yageIUwiwy@phenom.ffwll.local> (raw)
In-Reply-To: <YIqehmw+kG53LF3t@kroah.com>

On Thu, Apr 29, 2021 at 01:54:46PM +0200, Greg Kroah-Hartman wrote:
> On Thu, Apr 29, 2021 at 01:40:28PM +0200, Daniel Vetter wrote:
> > On Wed, Apr 28, 2021 at 11:52:49PM +0200, Hans de Goede wrote:
> > > Userspace could hold open a reference to the connector->kdev device,
> > > through e.g. holding a sysfs-atrtribute open after
> > > drm_sysfs_connector_remove() has been called. In this case the connector
> > > could be free-ed while the connector->kdev device's drvdata is still
> > > pointing to it.
> > > 
> > > Give drm_connector devices there own device type, which allows
> > > us to specify our own release function and make drm_sysfs_connector_add()
> > > take a reference on the connector object, and have the new release
> > > function put the reference when the device is released.
> > > 
> > > Giving drm_connector devices there own device type, will also allow
> > > checking if a device is a drm_connector device with a
> > > "if (device->type == &drm_sysfs_device_connector)" check.
> > > 
> > > Note that the setting of the name member of the device_type struct will
> > > cause udev events for drm_connector-s to now contain DEVTYPE=drm_connector
> > > as extra info. So this extends the uevent part of the userspace API.
> > > 
> > > Signed-off-by: Hans de Goede <hdegoede@redhat.com>
> > 
> > Are you sure? I thought sysfs is supposed to flush out any pending
> > operations (they complete fast) and handle open fd internally?
> 
> Yes, it "should" :)

Thanks for confirming my vague memories :-)

Hans, pls drop this one.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch