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Groups > linux.debian.kernel > #91185

Bug#1127724: Regression: r8169 driver causes link flapping on Realtek RTL8111/8168 (rev 11) since kernel 6.12.69

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Hi George,

Thanks for your report.

On Thu, Feb 12, 2026 at 12:41:28PM +0300, George Koukiss wrote:
> Package: src:linux
> Version: 6.12.69-1
> Severity: important
> 
> Dear Maintainer,
> 
> After upgrading from kernel 6.12.63 to 6.12.69 on Debian 13, I am
> experiencing constant network disconnects (link flapping) on my Ethernet
> interface.
> 
> Hardware:
> Realtek Semiconductor Co., Ltd. RTL8111/8168/8211/8411 PCI Express Gigabit
> Ethernet Controller [10ec:8168] (rev 11)
> 
> Symptoms:
> The dmesg log shows the link going Up and Down repeatedly every few
> seconds/minutes. Sometimes it downgrades from 1Gbps to 100Mbps before
> dropping again.
> 
> Logs (dmesg):
> [ 5202.128177] r8169 0000:03:00.0 enp3s0: Link is Down
> [ 5205.071512] r8169 0000:03:00.0 enp3s0: Link is Up - 1Gbps/Full
> [ 5205.655468] r8169 0000:03:00.0 enp3s0: Link is Down
> [ 5223.796420] r8169 0000:03:00.0 enp3s0: Link is Up - 100Mbps/Full
> 
> Troubleshooting:
> 1. Booting back to kernel 6.12.63-1 resolves the issue completely (no Link
> Down events).
> 2. The issue persists across different cables/ports on the newer kernel.
> 3. This appears to be a regression in the r8169 driver between .63 and .69.
> 
> Please let me know if you need more logs or testing.

It would be great if you could bisect the problem. That would involve
compiling and testing a few kernels:

    git clone --single-branch -b linux-6.12.y https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git
    cd linux-stable
    git checkout v6.12.63
    cp /boot/config-$(uname -r) .config
    yes '' | make localmodconfig
    make savedefconfig
    mv defconfig arch/x86/configs/my_defconfig

    # test 6.12.63 to ensure this is "good"
    make my_defconfig
    make -j $(nproc) bindeb-pkg
    ... install the resulting .deb package and confirm the problem does not exist

    # test 6.12.69 to ensure this is "bad"
    git checkout v6.12.35
    make my_defconfig
    make -j $(nproc) bindeb-pkg
    ... install the resulting .deb package and confirm the problem exists.

With that confirmed, the bisection can start:

    git bisect start
    git bisect good v6.12.63
    git bisect bad v6.12.69

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, 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

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Bug#1127724: Regression: r8169 driver causes link flapping on Realtek RTL8111/8168 (rev 11) since kernel 6.12.69 Salvatore Bonaccorso <carnil@debian.org> - 2026-02-12 11:40 +0100

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