Em Tue, 5 Apr 2016 08:10:11 +0200 Takashi Iwai <tiwai@xxxxxxx> escreveu: > 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. I agree. Let's first fix MC races first, then address the multi-driver issues. Only after having those fixed, we should look at the sound/usb patch. Ok, we could keep it on some testing tree, but, IMHO, it doesn't make any sense to submit it to review, while the core is not fixed. > 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. Works for me. After we have this properly fixed and stabilized on media, I'll pass you a stable topic branch for you. This way, you can test a new version of the sound/usb patch and apply on your tree when it fits well for you. > > 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 -- Cheers, Mauro -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
