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[2001:1c00:c1e:bf00:1054:9d19:e0f0:8214]) by smtp.gmail.com with ESMTPSA id t15sm2296998edr.55.2021.04.29.05.33.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 29 Apr 2021 05:33:18 -0700 (PDT) Subject: Re: [PATCH 1/9] drm/connector: Make the drm_sysfs connector->kdev device hold a reference to the connector To: Daniel Vetter , Greg Kroah-Hartman Cc: Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Guenter Roeck , Heikki Krogerus , intel-gfx , dri-devel@lists.freedesktop.org, platform-driver-x86@vger.kernel.org, linux-usb@vger.kernel.org References: <20210428215257.500088-1-hdegoede@redhat.com> <20210428215257.500088-2-hdegoede@redhat.com> From: Hans de Goede Message-ID: <4e78d188-f257-ad33-e703-bcbc54a30c31@redhat.com> Date: Thu, 29 Apr 2021 14:33:17 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org Hi, On 4/29/21 2:04 PM, Daniel Vetter wrote: > 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 >>> >>> 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. Please see my earlier reply to your review of this patch, it is still needed but for a different reason: """ We still need this change though to make sure that the "drm/connector: Add drm_connector_find_by_fwnode() function" does not end up following a dangling drvdat pointer from one if the drm_connector kdev-s. The class_dev_iter_init() in drm_connector_find_by_fwnode() gets a reference on all devices and between getting that reference and it calling drm_connector_get() - drm_connector_unregister() may run and drop the possibly last reference to the drm_connector object, freeing it and leaving the kdev's drvdata as a dangling pointer. """ This is actually why I added it initially, and while adding it I came up with this wrong theory of why it was necessary independently of the drm_connector_find_by_fwnode() addition, sorry about that. Regards, Hans