[Bug] soft lockup in neigh_timer_handler in Linux kernel v6.12

[Luka <luka.2016.cs@gmail.com>]

Dear Linux Kernel Maintainers,

I hope this message finds you well.

I am writing to report a potential vulnerability I encountered during
testing of the Linux Kernel version v6.12.

Git Commit: adc218676eef25575469234709c2d87185ca223a (tag: v6.12)

Bug Location: neigh_timer_handler+0xc17/0xfe0 net/core/neighbour.c:1148

Bug report: https://pastebin.com/06NiBtXm

Entire kernel config: https://pastebin.com/MRWGr3nv

Root Cause Analysis:

A soft lockup occurs in the neighbor subsystem due to prolonged
execution within neigh_timer_handler(), where repeated neighbor entry
invalidation and associated routing operations (e.g.,
ipv4_link_failure() and arp_error_report()) lead to excessive CPU
occupation without yielding, triggering the kernel watchdog.

At present, I have not yet obtained a minimal reproducer for this
issue. However, I am actively working on reproducing it, and I will
promptly share any additional findings or a working reproducer as soon
as it becomes available.

Thank you very much for your time and attention to this matter. I
truly appreciate the efforts of the Linux kernel community.

Best regards,
Luka