gstreamer 1.20: v4l2bufferpool spams "newly allocated buffer is not free"

[Nicolas Dufresne]

Le mardi 28 juin 2022 à 22:53 +0200, Michiel Konstapel via gstreamer-devel a
écrit :
> On 28-06-2022 22:13, Michiel Konstapel wrote:
> > On 27-06-2022 22:24, Nicolas Dufresne via gstreamer-devel wrote:
> > > Le dimanche 26 juin 2022 à 14:30 +0200, Michiel Konstapel a écrit :
> > > > On 25-06-2022 17:34, Nicolas Dufresne via gstreamer-devel wrote:
> > > > > > It's a very common Logitech C920 webcam (but I've seen the same 
> > > > > > message
> > > > > > with a Z-Cam M3 camera). I think that uses a generic UVC driver? 
> > > > > > Anything
> > > > > > I can run to get you more info?
> > > > > > 
> > > > > I'm asking as I cannot reproduce, and from the look of it, the 
> > > > > trace implies
> > > > > is will leak data. Which Kernel? Have you tested with your own 
> > > > > GStreamer
> > > > > build (main branch)?
> > > > $ uname -a
> > > >   Linux xubuntux 5.4.0-121-generic #137-Ubuntu SMP Wed Jun 15 
> > > > 13:33:07 UTC 2022
> > > That might explain the discrepancy, this is an old kernel, its quite 
> > > likely this
> > > is a kernel bug and its fixed in newer kernels. Make sure to try more 
> > > recently
> > > Ubuntu and check. If it is, you likely can request a backport to Ubuntu,
> > > assuming this isn't an EOL version you are using.
> > > 
> > > > x86_64 x86_64 x86_64 GNU/Linux
> > > > Gstreamer is built from source, from the 1.20.3 tag.
> > > > I have also just built it from main (commit
> > > > 0e551871c45a1b9fd67d99d2d4f31a983f1b3217) and that shows the effect 
> > > > as well.
> > > > Michiel
> > 
> > Alas, not quite. I've upgraded to Ubuntu 22.04 which has
> > 
> > $ uname -a
> > Linux xubuntux 5.15.0-40-generic #43-Ubuntu SMP Wed Jun 15 12:54:21 
> > UTC 2022 x86_64 x86_64 x86_64 GNU/Linux
> > 
> > But the problem persists.
> 
> 
> Another data point: I have another video device, on /dev/video0, which 
> is the webcam inside my Valve Index VR headset. That one does NOT 
> produce the warnings! I tried unplugging the headset and replugging the 
> Logitech C920 so that's on /dev/video0 (and the only webcam) but that 
> doesn't help: it still spews warnings.
> 

I'd be curious to see the value or &pool->buffer_state[group->buffer.index] when
that warning triggers. I fail to see how we actually endup in that situation. I
wonder if there is a relation with:

https://gitlab.freedesktop.org/gstreamer/gstreamer/-/issues/1087

And associated merge request. Did you already tried ?

https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/2007


Nicolas