Messages in this thread | | | Subject | Re: [PATCH 3/3] drivers/media/media-device: fix double free bug in _unregister() | From | Shuah Khan <> | Date | Wed, 15 Jun 2016 15:50:47 -0600 |
| |
On 06/15/2016 02:37 PM, Max Kellermann wrote: > On 2016/06/15 22:32, Shuah Khan <shuahkh@osg.samsung.com> wrote: >> This change introduces memory leaks, since drivers are relying on >> media_device_unregister() to free interfaces. > > This is what I thought, too, until I checked the code paths. Who adds > entries to that list? Only media_gobj_create() does, and only when > type==MEDIA_GRAPH_INTF_DEVNODE. That is called via > media_interface_init(), via media_devnode_create(). > > In the whole kernel, there are two calls to media_devnode_create(): > one in dvbdev.c and another one in v4l2-dev.c. Both callers take care > for freeing their interface. Both would crash if somebody else would > free it for them before they get a chance to do it. Which is the very > thing my patch addresses. > > Did I miss something? >
Yes media_devnode_create() creates the interfaces links and these links are deleted by media_devnode_remove(). media_device_unregister() still needs to delete the interfaces links. The reason for that is the API dynalic use-case.
Drivers (other than dvb-core and v4l2-core) can create and delete media devnode interfaces during run-time, hence media_devnode_remove() has to call media_remove_intf_links(). However, driver isn't required to call media_devnode_remove() and media-core can't enforce that. So it is safe for media_device_unregister() to remove interface links if the list isn't empty. If driver does delete them, media_device_unregister() has nothing to do since the list is going to be empty.
So removing kfree() from media_device_unregister() isn't the correct fix.
I don't see the stack trace for the double free error you are seeing? Could it be that there is a driver problem in the order in which it is calling media_device_unregister()?
thanks, -- Shuah
| |