Opening a bug report for this thread on the debian-kernel list. Ben. 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. Best regards, Roland Schwarzkopf
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.
You would need to search for in https://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.y https://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.
Regards,
Salvatore
Hi Salvatore, 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? Best Regards, Roland
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. 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
FWIW, it (as usual) would be very important to know if this happens with mainline as well, as that determines if it's a general problem or a backporting problem -- and the outcome, strictly speaking, determines if the developers of the change in question or the stable team are responsible. If we are lucky that distinction does not matter, but if we are unlucky neither camp might look into this as of now. I wrote more about this at length here: https://linux-regtracking.leemhuis.info/post/frequent-reasons-why-linux-kernel-bug-reports-are-ignored/ But yes, given that 5.10.y is quite old, it might be easier to test more recent stable series first. But if they show the same problem, please test mainline -- and ideally try if reverting is able to resolve the problem. Ciao, Thorsten
Hi all,
as well as mainline 6.19-rc1. With all three kernel versions, a
different problem occurs: I can't even start the virtual machine.
The relevant journal entry is:
Dec 19 17:25:41 iblis libvirtd[438]: error creating macvtap interface
macvtap0@eno1 (08:00:27:25:16:0c): Operation not supported
I then searched in the commit log for the upstream commit of the one I
found when bisecting the issue. It is a6cec0bcd342, which git describe
says is v5.18-rc1-423-ga6cec0bcd342. Therefore I decided to also test
the two longterm versions before and after that commit was introduced:
5.15.197 and 6.1.159. With both kernel versions I found the same
behavior as with the stable and mainline versions.
So on all newer kernel versions I tested behave identical, but different
than the latest release in the 5.10.y branch.
I'm not sure if I caused this behaviour by making a mistake during
building the kernels - I don't have much experience in that area. I used
the same steps Salvatore gave me for bisecting the issue for the
different versions, i.e.,
cp /boot/config-$(uname -r) .config
yes '' | make localmodconfig
make savedefconfig
mv defconfig arch/x86/configs/my_defconfig
make my_defconfig
make -j $(nproc) bindeb-pkg
Best regards,
Roland
Hi all, [...] The bug is this: - libvirtd wrongly used to use NLM_F_CREATE (0x400) and NLM_F_EXCL (0x200) flags on an RTM_DELLINK operation. These flags are only semantically valid for NEW-type operations. - rtnetlink is rather lax about checking the flags on operations, so these unsupported flags had no effect. - rtnetlink can now support NLM_F_BULK (0x200) on some DEL-type operations. If the flag is used but is not valid for the specific operation then the operation now fails with EOPNOTSUPP. Since NLM_F_EXCL == NLM_F_BULK and RTM_DELLINK does not support bulk operations, libvirtd now hits this error case. I have not tested with mainline, but in principle the same issue should occur with any other kernel version that has commit a6cec0bcd342 "net: rtnetlink: add bulk delete support flag" together with an older version of libvirt. This was fixed in libvirt commit 1334002340b, which appears to have gone into version 7.1.0, but Debian 11 "bullseye" has 7.0.0. We can certainly fix the libvirt side of this in Debian, but this also sounds like a case where the kernel should work around known buggy user- space. On the other hand, this has been upstream for over 3 years so maybe it doesn't make sense now. Please let me know whether I (or anyone) should try to implement a workaround for this in the kernel. Ben.
@stable team and/or @net maintainers: this imho needs a judgement call
from your side. See below for details.
End of October 2025 in parallel with 5b22f62724a0a0 ("net: rtnetlink:
fix module reference count leak issue in rtnetlink_rcv_msg") [v6.0-rc2],
which is a fix for the former.
Could not find that commit when looking briefly, but that version was
released 2021-03-01.
Yeah, I tend to the latter as well (the @net maintainers can speak up if
the disagree). But we have one more middle-ground option here maybe the
@stable team could do: revert the backports of 1550f3673972c5 and
5b22f62724a0a0 from 5.10.y, unless they are strongly needed there.
Ciao, Thorsten
Hi, https://gitlab.com/libvirt/libvirt/-/commit/81334002340be6bd3a1a34c6584a85fe25cc049c Regards, Salvatore
Ben, based on the fact that you reassigned the bug to libvirt, I understand that you are not going to address this in the kernel. Is that correct? To be honest I'm not particularly interested in pursuing updates to oldoldstable, especially considering that it'll be out of LTS support in just a few months. Does anyone know if there's a way to flag the LTS folks so that they will take a look and consider whether to take a bug on? Otherwise I'd be inclined to just close this and invite users affected by the issue to move to a supported release. Thanks.
Correct. I or another member of the LTS team will take care of this. Ben.
Sounds good. Thank you!