Re: [REGRESSION][BISECTED][STABLE] MT7925: mDNS and IPv6 broken in kernel 6.14.3 and above

[Niklas Schnelle <niks@kernel.org>]

On Wed, 2025-04-30 at 06:47 +0000, Mingyen Hsieh (謝明諺) wrote:
> On Wed, 2025-04-30 at 01:14 +0000, fossben@pm.me wrote:
> > 
> > External email : Please do not click links or open attachments until
> > you have verified the sender or the content.
> > 
> > 
> > Hello all,
> > 
> > After upgrading to 6.14.3 on my PC with a MT7925 chip, I noticed that
> > I could no longer ping *.local addresses provided by Avahi. In
> > addition, I also noticed that I was not able to get a DHCP IPv6
> > address from my router, no matter how many times I rebooted the
> > router or reconnected with NetworkManager.
> > 
> > Reverting to 6.14.2 fixes both mDNS and IPv6 addresses immediately.
> > Going back to 6.14.3 immediately breaks mDNS again, but the IPv6
> > address will stay there for a while before disappearing later,
> > possibly because the DHCP lease expired? I am not sure exactly when
> > it stops working.
> > 
> > I've done a kernel bisect between 6.14.2 and 6.14.3 and found the
> > offending commit that causes mDNS to fail:
> > 
> > commit 80007d3f92fd018d0a052a706400e976b36e3c87
> > Author: Ming Yen Hsieh <mingyen.hsieh@mediatek.com>
> > Date:   Tue Mar 4 16:08:50 2025 -0800
> > 
> >     wifi: mt76: mt7925: integrate *mlo_sta_cmd and *sta_cmd
> > 
> >     commit cb1353ef34735ec1e5d9efa1fe966f05ff1dc1e1 upstream.
> > 
> >     Integrate *mlo_sta_cmd and *sta_cmd for the MLO firmware.
> > 
> >     Fixes: 86c051f2c418 ("wifi: mt76: mt7925: enabling MLO when the
> > firmware supports it")
> > 
> >  drivers/net/wireless/mediatek/mt76/mt7925/mcu.c | 59 ++++-----------
> > --------------------------------------------
> >  1 file changed, 4 insertions(+), 55 deletions(-)
> > 
> > I do not know if this same commit is also causing the IPv6 issues as
> > testing that requires quite a bit of time to reproduce. What I do
> > know with certainty as of this moment is that it definitely breaks in
> > kernel 6.14.3.
> > 
> > I've attached my hardware info as well as dmesg logs from the last
> > working kernel from the bisect and 6.14.4 which exhibits the issue.
> > Please let me know if there's any other info you need.
> > 
> > Thanks!
> > Benjamin Xiao
> 
> Hi,
> 
> Thanks for reporting this issue, we will aim into this.
> 
> Can you provide me with your testing steps?
> 
> Best Regards,
> Yen.
> 

Hi Yan,

I see the same IPv6 issue on my Framework 13 (Ryzen 5 AI 340) with an
mt7925e WiFI module. My setup is just a home router with native IPv6
both for my uplink and in the LAN. The problems with IPv6 can already
be seen just in the LAN for example by checking which IP was used for
SSH, in my setup it should always be IPv6 but falls back to IPv4 in the
broken state.

As another data point, I tried reverting cb1353ef3473 ("wifi: mt76:
mt7925: integrate *mlo_sta_cmd and *sta_cmd") on top of 6.15.-rc4. This
fully restores IPv6 for me. Also note I'm running this with the mt7925
firmware version 20250425073330 from linux-firmware's master branch as
I had some dropped connections with earlier firmware.

So it definitely looks like that commit also broke IPv6 and not just
mDNS. Note that if if I use DHCPv6 instead of router advertisements, on
the latest firmware, but without the revert, I get a global IPv6
address added to the interface but then native IPv6 addresses are still
uncreachable. With the offending patch reverted my SSH session to an
IPv6 only host works fine and is stable. Also I'd be willing to test a
proper fix as I rely on IPv6 heavily due to having to use CGNAT for
IPv4 but not for IPv6.


Thanks,
Niklas