On Tue, 05 Apr 2016 05:35:55 +0200, Shuah Khan wrote: > > There are known problems with media device life time management. When media > device is released while an media ioctl is in progress, ioctls fail with > use-after-free errors and kernel hangs in some cases. > > Media Device can be in any the following states: > > - Allocated > - Registered (could be tied to more than one driver) > - Unregistered, not in use (media device file is not open) > - Unregistered, in use (media device file is not open) > - Released > > When media device belongs to more than one driver, registrations should be > tracked to avoid unregistering when one of the drivers does unregister. A new > num_drivers field in the struct media_device covers this case. The media device > should be unregistered only when the last unregister occurs with num_drivers > count zero. > > When a media device is in use when it is unregistered, it should not be > released until the application exits when it detects the unregistered > status. Media device that is in use when it is unregistered is moved to > to_delete_list. When the last unregister occurs, media device is unregistered > and becomes an unregistered, still allocated device. Unregister marks the > device to be deleted. > > When media device belongs to more than one driver, as both drivers could be > unbound/bound, driver should not end up getting stale media device that is > on its way out. Moving the unregistered media device to to_delete_list helps > this case as well. > > I ran bind/unbind loop tests on uvcvideo, au0828, and snd-usb-audio while > running application that does ioctls. Didn't see any use-after-free errors > on media device. A couple of known issues seen: > > 1. When application exits, cdev_put() gets called after media device is > released. This is a known issue to resolve and Media Device Allocator > can't solve this one. > 2. When au0828 module is removed and then ioctls fail when cdev_get() looks > for the owning module as au0828 is very often the module that owns the > media devnode. This is a cdev related issue that needs to be resolved and > Media Device Allocator can't solve this one. > > Shuah Khan (5): > media: Add Media Device Allocator API > media: Add driver count to keep track of media device registrations > media: uvcvideo change to use Media Device Allocator API > media: au0828 change to use Media Device Allocator API > sound/usb: Use Media Controller API to share media resources I don't think we need to include usb-audio patch at this stage yet. The most important thing for now is to improve / stabilize the API itself so that other drivers can use it as is. Once when the API is really stabilized, we create a solid git branch that may be based for multiple subsystems, and I'll merge usb-audio stuff through sound git tree. Also, the previous usb-audio MC implementation had a few serious bugs, including quirk NULL dereference. See the bugzilla below for some fix patches to 4.6-rc1: https://bugzilla.kernel.org/show_bug.cgi?id=115561 Feel free to fold them in, if they are still valid. thanks, Takashi _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
