Mythtv can no longer access DVB devices after ubuntu 24.04 upgrade

[Simon Lambourn]

Before upgrade, mythtv was working with two separate DVB tuners.
After upgrade, mythtv can see the /dev/dvb adapters but cannot access them ("could not get card info for /dev/dvb/adapter0/frontend0"). All recordings since the upgrade to ubuntu 24.04 have failed.

The devices seem to have the right permissions and mythtv-backend is running as mythtv, which is a member of the video group:

ls -al /dev/dvb/adapter?
/dev/dvb/adapter0:
total 0
drwxr-xr-x 2 root root 120 Jun 3 10:21 .
drwxr-xr-x 4 root root 80 Jun 3 10:21 ..
crw-rw----+ 1 root video 212, 1 Jun 3 10:21 demux0
crw-rw----+ 1 root video 212, 2 Jun 3 10:21 dvr0
crw-rw----+ 1 root video 212, 0 Jun 3 10:21 frontend0
crw-rw----+ 1 root video 212, 3 Jun 3 10:21 net0

/dev/dvb/adapter1:
total 0
drwxr-xr-x 2 root root 120 Jun 3 10:21 .
drwxr-xr-x 4 root root 80 Jun 3 10:21 ..
crw-rw----+ 1 root video 212, 5 Jun 3 10:21 demux0
crw-rw----+ 1 root video 212, 6 Jun 3 10:21 dvr0
crw-rw----+ 1 root video 212, 4 Jun 3 10:21 frontend0
crw-rw----+ 1 root video 212, 7 Jun 3 10:21 net0

lsof /dev/dvb and fuser /dev/dvb do not report any users of the devices (I hope I am using the command correctly)

Expected behaviour: mythtv can access the DVB tuners and use them for live TV & recordings, as previously.

Ubuntu is now 24.04 Noble Numbat, after upgrading from 23.10.
Mythtv is now 2:34.0+fixes.20240210.e3e165a1-0ubuntu6

I am using the web frontend to access mythtv backend setup.
mythbackend.log has the following entries:

2024-06-03T10:56:06.285978+01:00 gracix2 mythbackend: mythbackend[2706]: E HTTP0 cardutil.cpp:1249 (OpenVideoDevice) CardUtil: Can't open DVB frontend (/dev/dvb/adapter0/frontend0) for /dev/dvb/adapter0/frontend0.#012#011#011#011eno: Device or resource busy (16)
2024-06-03T10:56:06.448387+01:00 gracix2 mythbackend: mythbackend[2706]: E HTTP0 cardutil.cpp:928 (ProbeCurrentDeliverySystem) CardUtil: open failed (/dev/dvb/adapter0/frontend0)#012#011#011#011eno: Device or resource busy (16)
2024-06-03T10:56:06.448744+01:00 gracix2 mythbackend: mythbackend[2706]: E HTTP0 cardutil.cpp:1249 (OpenVideoDevice) CardUtil: Can't open DVB frontend (/dev/dvb/adapter1/frontend0) for /dev/dvb/adapter1/frontend0.#012#011#011#011eno: Device or resource busy (16)
2024-06-03T10:56:06.449107+01:00 gracix2 mythbackend: mythbackend[2706]: E HTTP0 cardutil.cpp:928 (ProbeCurrentDeliverySystem) CardUtil: open failed (/dev/dvb/adapter1/frontend0)#012#011#011#011eno: Device or resource busy (16)

It says the device is busy, but as far as I can tell there is nothing using the device?

Thank you in advance for any help.

ProblemType: Bug
DistroRelease: Ubuntu 24.04
Package: mythtv 2:34.0+fixes.20240210.e3e165a1-0ubuntu6
ProcVersionSignature: Ubuntu 6.8.0-31.31-generic 6.8.1
Uname: Linux 6.8.0-31-generic x86_64
ApportVersion: 2.28.1-0ubuntu3
Architecture: amd64
CasperMD5CheckResult: unknown
CurrentDesktop: ubuntu:GNOME
Date: Mon Jun 3 10:57:46 2024
Installed_mythtv_dbg: 0.0
PackageArchitecture: all
SourcePackage: mythtv
UpgradeStatus: No upgrade log present (probably fresh install)

[Simon Lambourn (simon-lambourn-o)]

dmesg output:

$ sudo dmesg |grep dvb
[ 21.100050] saa7134_dvb: dvb_init() allocating 1 frontend
[ 21.248215] em28xx 2-2:1.0: dvb set to isoc mode.
[ 21.596207] dvbdev: DVB: registering new adapter (saa7130[0])
[ 21.596232] dvbdev: dvb_create_media_entity: media entity 'NXP TDA10048HN DVB-T' registered.
[ 21.599068] dvbdev: dvb_create_media_entity: media entity 'dvb-demux' registered.
[ 21.724204] tda10048_firmware_upload: waiting for firmware upload (dvb-fe-tda10048-1.0.fw)...
[ 30.545497] dvbdev: DVB: registering new adapter (2-2:1.0)
[ 30.545509] dvbdev: dvb_create_media_entity: media entity 'Silicon Labs Si2168' registered.
[ 30.547906] dvbdev: dvb_create_media_entity: media entity 'dvb-demux' registered.
[ 30.551147] em28xx: Registered (Em28xx dvb Extension) extension
[ 78.147389] si2168 11-0064: downloading firmware from file 'dvb-demod-si2168-b40-01.fw'
[ 78.845473] si2168 11-0064: downloading firmware from file 'dvb-demod-si2168-b40-01.fw'