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

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Message-ID: <EmWnO5b-acRH1TXbGnkx41eJw654vmCR-8_xMBaPMwexCnfkvKCdlU5u19CGbaapJ3KRu-l3B-tSUhf8CCQwL0odjo6Cd5YG5lvNeB-vfdg=@pm.me>
Date: Wed, 30 Apr 2025 01:14:28 +0000
From: fossben@...me
To: Ming Yen Hsieh <mingyen.hsieh@...iatek.com>, "stable@...r.kernel.org" <stable@...r.kernel.org>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "regressions@...ts.linux.dev" <regressions@...ts.linux.dev>, "linux-mediatek@...ts.infradead.org" <linux-mediatek@...ts.infradead.org>, "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>
Subject: [REGRESSION][BISECTED][STABLE] MT7925: mDNS and IPv6 broken in kernel 6.14.3 and above

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@...iatek.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
View attachment "inxi.txt" of type "text/plain" (3181 bytes)

View attachment "dmesg_working.txt" of type "text/plain" (127820 bytes)

View attachment "dmesg_bad.txt" of type "text/plain" (118872 bytes)