** Description changed:
[Impact]
Linux 6.18 added a "struct file *filp" parameter to v4l2_fh_add() and
v4l2_fh_del() (include/media/v4l2-fh.h).
v4l2loopback 0.12.7 still calls both with the old single-argument signature,
so the DKMS build fails against the noble 7.0 HWE kernel:
v4l2loopback.c:2089: error: too few arguments to function 'v4l2_fh_add'
v4l2loopback.c:2117: error: too few arguments to function 'v4l2_fh_del'
The impact is not limited to the virtual camera.
dkms autoinstall runs from /etc/kernel/header_postinst.d/dkms, so the build
failure aborts the kernel header postinst with exit status 11 and leaves the
kernel meta package unconfigured.
- Every subsequent apt operation, including security updates, then fails
- until the user removes v4l2loopback-dkms by hand.
+ Later apt operations then exit non-zero, including security updates, and
+ the kernel package stays unconfigured until v4l2loopback-dkms is removed
+ or a fixed version is installed.
linux-hwe-7.0 is published in both noble-updates and noble-security, so
affected systems receive the kernel automatically.
37 users are affected and 25 duplicates were filed within a week.
Fixing only the call signature is not enough.
- Linux 6.18 also requires the new file_to_v4l2_fh() accessor to reach the file
handle, so with only the signature fix the module builds and loads but oopses
as soon as a consumer opens the device:
+ Linux 6.18 also requires the new file_to_v4l2_fh() accessor to reach the file
handle, so with only the signature fix the module builds and loads but oopses
on the first ioctl a consumer issues against the device:
BUG: unable to handle page fault for address: fffffffffffffffc
RIP: 0010:vidioc_reqbufs+0xa2/0x3b0 [v4l2loopback]
Both fixes are in this upload.
[Test Plan]
- On a noble system with v4l2loopback-dkms installed:
+ On a noble system that has v4l2loopback-dkms installed and does not yet have
the 7.0 HWE headers:
sudo apt-get install -y linux-headers-7.0.0-28-generic
- Without the fix
run-parts: /etc/kernel/header_postinst.d/dkms exited with return code 11
dpkg: error processing package linux-headers-7.0.0-28-generic
(--configure)
E: Sub-process /usr/bin/dpkg returned an error code (1)
- apt stays broken until v4l2loopback-dkms is removed.
+ sudo dpkg --audit
+
+ dpkg --audit lists both linux-headers-7.0.0-28-generic and v4l2loopback-
+ dkms as half configured.
- With the fix
sudo apt-get install -y -t noble-proposed v4l2loopback-dkms
dkms status v4l2loopback
The header package configures cleanly and dkms status reports v4l2loopback
installed for 7.0.0-28-generic.
+ "sudo dpkg --audit" now prints nothing, without removing v4l2loopback-dkms.
The GA kernel must be unaffected on the same system:
sudo apt-get install -y linux-headers-6.8.0-136-generic
dkms status v4l2loopback
- The module must also build for 6.8.0-136-generic.
- The oops fix, on a machine running 7.0:
+ The module must also build for the GA kernel, and the streaming check below
must pass on it as well.
+ The oops fix, booted into 7.0 and then repeated on the GA kernel. video_nr
pins the device so a real webcam cannot take the number:
- sudo modprobe v4l2loopback devices=1
- ffmpeg -re -f lavfi -i testsrc=size=640x480:rate=30 -t 60 -f v4l2
/dev/video0 &
- ffplay -f v4l2 -i /dev/video0
+ sudo modprobe v4l2loopback devices=1 video_nr=42 max_buffers=4
+ sudo dmesg -C
+ ffmpeg -loglevel error -re -f lavfi -i testsrc=size=640x480:rate=30 -t 30
\
+ -f v4l2 /dev/video42 &
+ ffmpeg -loglevel error -f v4l2 -i /dev/video42 -t 25 -f null -
+ dmesg
- Streaming must run to completion with no oops in dmesg.
+ Both ffmpeg commands must exit 0 and dmesg must contain no "Oops", "BUG:" or
"page fault" entry.
Without the accessor fix the consumer is killed and dmesg shows the
vidioc_reqbufs page fault above.
[Where problems could occur]
If either compat macro is wrong, the module either stops building on one
of the two kernels noble supports, leaving apt in the broken state this
SRU is fixing, or resolves the opener incorrectly and oopses on the
first ioctl a consumer issues.
[Other Info]
Fixed upstream in v4l2loopback 0.15.2 by
https://github.com/v4l2loopback/v4l2loopback/commit/3b09d3c53997f5f05e8d0db9222706585dbbe67a
Fix compilation with linux-6.18.0
(with its follow-up ce8474158c6e, which applies the same change to
v4l2_fh_del)
and in 0.15.3 by
https://github.com/v4l2loopback/v4l2loopback/commit/6b33fe1f682881eb268ab9fc85f231acc5564ac8
use linux>=6.18 accessor for v4l2->private_data
[ORIGINAL DESCRIPTION]
v4l2loopback.c: In function ‘v4l2_loopback_open’:
v4l2loopback.c:2089:9: error: too few arguments to function ‘v4l2_fh_add’
2089 | v4l2_fh_add(&opener->fh);
| ^~~~~~~~~~~
In file included from
/usr/src/linux-headers-7.0.0-28-generic/include/media/v4l2-subdev.h:17,
from
/usr/src/linux-headers-7.0.0-28-generic/include/media/v4l2-device.h:13,
from v4l2loopback.c:31:
/usr/src/linux-headers-7.0.0-28-generic/include/media/v4l2-fh.h:97:6: note:
declared here
97 | void v4l2_fh_add(struct v4l2_fh *fh, struct file *filp);
| ^~~~~~~~~~~
v4l2loopback.c: In function ‘v4l2_loopback_close’:
v4l2loopback.c:2117:9: error: too few arguments to function ‘v4l2_fh_del’
2117 | v4l2_fh_del(&opener->fh);
| ^~~~~~~~~~~
/usr/src/linux-headers-7.0.0-28-generic/include/media/v4l2-fh.h:125:6: note:
declared here
125 | void v4l2_fh_del(struct v4l2_fh *fh, struct file *filp);
| ^~~~~~~~~~~
ProblemType: Package
DistroRelease: Ubuntu 24.04
Package: linux-headers-7.0.0-28-generic 7.0.0-28.28~24.04.1
ProcVersionSignature: Ubuntu 6.17.0-35.35~24.04.1-generic 6.17.13
Uname: Linux 6.17.0-35-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.28.2-0ubuntu0.1
Architecture: amd64
AudioDevicesInUse:
USER PID ACCESS COMMAND
/dev/snd/controlC0: tom-brown 2572 F.... wireplumber
/dev/snd/controlC1: tom-brown 2572 F.... wireplumber
/dev/snd/seq: tom-brown 2567 F.... pipewire
CRDA: N/A
CasperMD5CheckResult: pass
Date: Thu Jul 16 22:52:40 2026
ErrorMessage: installed linux-headers-7.0.0-28-generic package
post-installation script subprocess returned error exit status 11
InstallationDate: Installed on 2025-12-20 (209 days ago)
InstallationMedia: Ubuntu 24.04.3 LTS "Noble Numbat" - Release amd64
(20250805.1)
Lsusb:
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 002: ID 046d:c52b Logitech, Inc. Unifying Receiver
Bus 001 Device 003: ID 8087:0a2b Intel Corp. Bluetooth wireless interface
Bus 001 Device 004: ID 0bda:57c3 Realtek Semiconductor Corp.
Integrated_Webcam_HD
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
MachineType: Dell Inc. Precision 7510
ProcFB: 0 i915drmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-6.17.0-35-generic
root=UUID=0cd37cd1-1382-4191-9107-b090419b644e ro quiet splash vt.handoff=7
Python3Details: /usr/bin/python3.12, Python 3.12.3, python3-minimal,
3.12.3-0ubuntu2.1
PythonDetails: N/A
RelatedPackageVersions: grub-pc N/A
SourcePackage: linux-hwe-7.0
Title: package linux-headers-7.0.0-28-generic 7.0.0-28.28~24.04.1 failed to
install/upgrade: installed linux-headers-7.0.0-28-generic package
post-installation script subprocess returned error exit status 11
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 03/09/2023
dmi.bios.release: 1.31
dmi.bios.vendor: Dell Inc.
dmi.bios.version: 1.31.3
dmi.board.name: 0MJ7KG
dmi.board.vendor: Dell Inc.
dmi.board.version: A00
dmi.chassis.type: 9
dmi.chassis.vendor: Dell Inc.
dmi.modalias:
dmi:bvnDellInc.:bvr1.31.3:bd03/09/2023:br1.31:svnDellInc.:pnPrecision7510:pvr:rvnDellInc.:rn0MJ7KG:rvrA00:cvnDellInc.:ct9:cvr:sku06D9:
dmi.product.family: Precision
dmi.product.name: Precision 7510
dmi.product.sku: 06D9
dmi.sys.vendor: Dell Inc.
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https://bugs.launchpad.net/bugs/2161037
Title:
v4l2loopback fails to build and then oopses on kernel 7.0 HWE
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