Re: [PATCH net v2] ipv6: addrconf: skip autoconf on unregistering devices

[Tetsuo Handa]

On 2026/05/14 22:18, Xu Rao wrote:
> So the no-patch baseline still triggers the leak in the same environment
> where both the proposed patch and the WARN_ON() diagnostic patch returned
> OK.
> 
> I agree that the WARN_ON() result does not prove the exact
> NETREG_UNREGISTERING hypothesis, because it did not trigger.  I also do
> not think this negative result is strong enough to disprove the race:
> this bug is timing-sensitive, and even adding the reg_state load, branch
> and WARN_ON() site can perturb the execution enough for a best-effort
> syzbot run not to hit the same interleaving.

Since easily reproducible cases have been fixed in
"unregister_netdevice: waiting for DEV to become free (8)",
cases reported in
"unregister_netdevice: waiting for DEV to become free (9)" and
afterwards are likely timing-dependent difficult-to-reproduce races.

Therefore, we need careful reasoning for why a patch can fix the problem.
Carrying my debug printk() patches in networking trees might help.