Hi all,

Roland Schwarzkopf reported to the Debian mailing list a problem which he encountered once updating in Debian from 5.10.244 to 5.10.247. The report is quoted below and found in https://lists.debian.org/debian-kernel/2025/12/msg00223.html

Roland did bisect the changes between 5.10.244 to 5.10.247 and found that the issue is introduced with 1550f3673972 ("net: rtnetlink: add bulk delete support flag") which is the backport to the 5.10.y series.

On Thu, Dec 18, 2025 at 02:59:55PM +0100, Roland Schwarzkopf wrote:

Hi Salvatore,

On 12/17/25 20:28, Salvatore Bonaccorso wrote:

...

Hi Roland,

I'm CC'ing Ben Hutchings directly as well as he takes care of the Debian LTS kernel updates. Idellly we make this as well a proper bug for easier tracking.

On Wed, Dec 17, 2025 at 01:35:54PM +0100, Roland Schwarzkopf wrote:

...

Hi there,

after upgrading to the latest kernel on Debian 11 (linux-image-5.10.0-37-amd64) I have an issue using libvirt with qemu/kvm virtual machines and macvtap networking. When a machine is shut down, libvirt can not delete the corresponding macvtap device. Thus, starting the machine again is not possible. After manually removing the macvtap device using `ip link delete` the vm can be started again.

In the journal the following message is shown:

Dec 17 13:19:27 iblis libvirtd[535]: error destroying network device macvtap0: Operation not supported

After downgrading the kernel to linux-image-5.10.0-36-amd64, the problem disappears. I tested this on a fresh minimal install of Debian 11 - to exclude that anything else on my production machines is causing this issue.

Since the older kernel does not have this issue, I assume this is related to the kernel and not to libvirt?

I tried to check for bug reports of the kernel package, but the bug tracker finds no reports and even states that the package does not exist (I used the "Bug reports" link on https://packages.debian.org/bullseye/linux-image-5.10.0-37-amd64). This left me a bit puzzled. Since I don't have experience with the debian bug reporting process, I had no other idea than writing to this list.

You would need to search for inhttps://bugs.debian.org/src:linux , but that said I'm not aware of any bug reports in that direction.

Would you be in the position of bisecting the problem as you can say that 5.10.244 is good and 5.10.247 is bad and regressed? If you can do that that would involve compiling a couple of kernels to narrow down where the problem is introduced:

 git clone --single-branch -b linux-5.10.yhttps://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git
 cd linux-stable
 git checkout v5.10.244
 cp /boot/config-$(uname -r) .config
 yes '' | make localmodconfig
 make savedefconfig
 mv defconfig arch/x86/configs/my_defconfig

 # test 5.10.244 to ensure this is "good"
 make my_defconfig
 make -j $(nproc) bindeb-pkg
 ... install the resulting .deb package and confirm it successfully boots / problem does not exist

 # test 5.10.247 to ensure this is "bad"
 git checkout v5.10.247
 make my_defconfig
 make -j $(nproc) bindeb-pkg
 ... install the resulting .deb package and confirm it fails to boot / problem exists

With that confirmed, the bisection can start:

 git bisect start
 git bisect good v5.10.244
 git bisect bad v5.10.247

In each bisection step git checks out a state between the oldest known-bad and the newest known-good commit. In each step test using:

 make my_defconfig
 make -j $(nproc) bindeb-pkg
 ... install, try to boot / verify if problem exists

and if the problem is hit run:

 git bisect bad

and if the problem doesn't trigger run:

 git bisect good

. Please pay attention to always select the just built kernel for booting, it won't always be the default kernel picked up by grub.

Iterate until git announces to have identified the first bad commit.

Then provide the output of

 git bisect log

In the course of the bisection you might have to uninstall previous kernels again to not exhaust the disk space in /boot. Also in the end uninstall all self-built kernels again.

I just did my first bisection \o/ (sorry)

Here are the results:

git bisect start # bad: [f964b940099f9982d723d4c77988d4b0dda9c165] Linux 5.10.247 git bisect bad f964b940099f9982d723d4c77988d4b0dda9c165 # good: [863b76df7d1e327979946a2d3893479c3275bfa4] Linux 5.10.244 git bisect good f52ee6ea810273e527a5d319e5f400be8c8424c1 # good: [dc9fdb7586b90e33c766eac52b6f3d1c9ec365a1] net: usb: lan78xx: Add error handling to lan78xx_init_mac_address git bisect good dc9fdb7586b90e33c766eac52b6f3d1c9ec365a1 # bad: [2272d5757ce5d3fb416d9f2497b015678eb85c0d] phy: cadence: cdns-dphy: Enable lower resolutions in dphy git bisect bad 2272d5757ce5d3fb416d9f2497b015678eb85c0d # bad: [547539f08b9e3629ce68479889813e58c8087e70] ALSA: usb-audio: fix control pipe direction git bisect bad 547539f08b9e3629ce68479889813e58c8087e70 # bad: [3509c748e79435d09e730673c8c100b7f0ebc87c] most: usb: hdm_probe: Fix calling put_device() before device initialization git bisect bad 3509c748e79435d09e730673c8c100b7f0ebc87c # bad: [a6ebcafc2f5ff7f0d1ce0c6dc38ac09a16a56ec0] net: add ndo_fdb_del_bulk git bisect bad a6ebcafc2f5ff7f0d1ce0c6dc38ac09a16a56ec0 # good: [b8a72692aa42b7dcd179a96b90bc2763ac74576a] hfsplus: fix KMSAN uninit-value issue in __hfsplus_ext_cache_extent() git bisect good b8a72692aa42b7dcd179a96b90bc2763ac74576a # good: [2b42a595863556b394bd702d46f4a9d0d2985aaa] m68k: bitops: Fix find_*_bit() signatures git bisect good 2b42a595863556b394bd702d46f4a9d0d2985aaa # good: [9d9f7d71d46cff3491a443a3cf452cecf87d51ef] net: rtnetlink: use BIT for flag values git bisect good 9d9f7d71d46cff3491a443a3cf452cecf87d51ef # bad: [1550f3673972c5cfba714135f8bf26784e6f2b0f] net: rtnetlink: add bulk delete support flag git bisect bad 1550f3673972c5cfba714135f8bf26784e6f2b0f # good: [c8879afa24169e504f78c9ca43a4d0d7397049eb] net: netlink: add NLM_F_BULK delete request modifier git bisect good c8879afa24169e504f78c9ca43a4d0d7397049eb # first bad commit: [1550f3673972c5cfba714135f8bf26784e6f2b0f] net: rtnetlink: add bulk delete support flag

Is there anything else I can do to help?

Is there soemthing missing?

Roland I think it would be helpful if you can test as well more recent stable series versions to confirm if the issue is present there as well or not, which might indicate a 5.10.y specific backporting problem.

#regzbot introduced: 1550f3673972c5cfba714135f8bf26784e6f2b0f

Regards, Salvatore