Re: [RFC PATCH v2 0/5] Media Device Allocator API

[Mauro Carvalho Chehab]

Em Tue, 5 Apr 2016 08:10:11 +0200
Takashi Iwai  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


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Re: [RFC PATCH v2 0/5] Media Device Allocator API

[Shuah Khan]

On 04/05/2016 12:10 AM, Takashi Iwai wrote:
> 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.

Agreed. I included snd-usb-audio as it provides a good test case for
multiple driver use-case. Yes it is a good idea to have a git branch
for wider testing.

> 
> 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.

I folded them in. It is unfortunate that these bugs were introduced towards
the end when I was making changes to address review comments and I didn't
catch them, especially the quirk NULL dereference.

thanks,
-- Shuah

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Re: [RFC PATCH v2 0/5] Media Device Allocator API

[Takashi Iwai]

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
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[RFC PATCH v2 0/5] Media Device Allocator API

[Shuah Khan]

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

 drivers/media/Makefile |   3 +-
 drivers/media/media-dev-allocator.c| 154 
 drivers/media/media-device.c   |  49 -
 drivers/media/media-devnode.c  |  10 +-
 drivers/media/usb/au0828/au0828-core.c |  40 +++--
 drivers/media/usb/au0828/au0828.h  |   1 +
 drivers/media/usb/uvc/uvc_driver.c |  36 ++--
 drivers/media/usb/uvc/uvcvideo.h   |   3 +-
 include/media/media-dev-allocator.h| 116 
 include/media/media-device.h   |  31 
 sound/usb/Kconfig  |   4 +
 sound/usb/Makefile |   2 +
 sound/usb/card.c   |  14 ++
 sound/usb/card.h   |   3 +
 sound/usb/media.c  | 320 +
 sound/usb/media.h  |  73 
 sound/usb/mixer.h  |   3 +
 sound/usb/pcm.c|  28 ++-
 sound/usb/quirks-table.h   |   1 +
 sound/usb/stream.c |   2 +
 sound/usb/usbaudio.h   |   6 +
 21 files changed, 862 insertions(+), 37 deletions(-)
 create mode 100644 drivers/media/media-dev-allocator.c
 create mode 100644 include/media/media-dev-allocator.h
 create mode 100644 sound/usb/media.c
 create mode 100644 sound/usb/media.h

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