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Sun, 20 Sep 2026 02:29:27 -0400 (EDT) Message-ID: <98538a44-63c3-455e-96f3-00124a825f9f@pobox.com> Date: Sat, 19 Sep 2026 23:29:26 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 6.12 0000/1102] 6.12.111-rc1 review To: Sasha Levin , Greg Kroah-Hartman , stable@vger.kernel.org, Kuniyuki Iwashima , Eric Dumazet Cc: patches@lists.linux.dev, linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, linux@roeck-us.net, shuah@kernel.org, patches@kernelci.org, lkft-triage@lists.linaro.org, pavel@nabladev.com, jonathanh@nvidia.com, f.fainelli@gmail.com, sudipm.mukherjee@gmail.com, rwarsow@gmx.de, conor@kernel.org, hargar@microsoft.com, broonie@kernel.org, achill@achill.org, sr@sladewatkins.com References: <20260917151539.408551884@linuxfoundation.org> <49dc2e4f-7a94-430c-8b02-6f3d422222f3@pobox.com> Content-Language: en-US From: "Barry K. Nathan" In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 9/19/26 10:07 AM, Sasha Levin wrote: > On Sat, Sep 19, 2026 at 03:54:25AM -0700, Barry K. Nathan wrote: >>> [   98.363843] RTNL: assertion failed at net/ipv6/mcast.c (1014) >>> [   98.363896] WARNING: CPU: 6 PID: 961 at net/ipv6/mcast.c:1014 __ipv6_dev_mc_dec+0x17b/0x190 [ipv6] > >> I bisected it to this patch: >> ipv6-mcast-don-t-hold-rtnl-for-ipv6_drop_membership-.patch. > > Your bisect is right, and thanks for chasing it all the way down -- > the splat is real and the patch you landed on is the trigger. > > I've dropped the ipv6 mcast RTNL conversion patches from the 6.12, 6.6 > and 5.15 queues. > >> If I take 6.12.110, apply the current stable-queue (as of commit >> 01b20bb84b994fdcda64fd07a66ba84c85d0168f), then revert the >> following patches: >> >> ipv6-mcast-don-t-hold-rtnl-for-ipv6_drop_membership-.patch >> ipv6-mcast-don-t-hold-rtnl-for-mcast_-socket-options.patch >> ipv6-mcast-use-copy-on-write-rcu-updates-in-ip6_mc_s.patch >> >> then the resulting kernel no longer shows these warnings at all. > > The root cause is a prerequisite we never picked up, rather than anything wrong > with the patches themselves. Upstream commit e01b193e0b50a ("ipv6: mcast: Use > in6_dev_get() in ipv6_dev_mc_dec().") is the commit in that series which > deletes the now-stale ASSERT_RTNL() from __ipv6_dev_mc_dec(), and it was never > backported to 6.12.y, 6.6.y or 5.15.y. So we took the patches that stop holding > RTNL across the setsockopt paths while the assertion they were meant to retire > was still sitting there -- hence net/ipv6/mcast.c:1014 firing on every > IPV6_DROP_MEMBERSHIP. The queued patches are byte-identical cherry-picks of the > upstream commits; this is a series-ordering gap on our side, not a botched > backport. > > 7.2 and 6.18 carry the whole series, including e01b193e0b50a, so they > are not affected and keep their copies. > > One difference from your experiment: I removed four patches rather than the > three you reverted. The extra one is 1767bb2d47b7 ("ipv6: mcast: Don't hold > RTNL for IPV6_ADD_MEMBERSHIP and MCAST_JOIN_GROUP."), which is a pure refactor > of the join path and was only ever queued as a dependency of the others. It is > harmless on its own so consistent with you not needing to revert it, but with > the rest gone there is no reason to keep it, and dropping it keeps the series > intact for a clean requeue. > > The plan is to requeue the complete ordered set, e01b193e0b50a included, > once this RC is out. Thanks for taking care of this! I have now retested with 6.12.110 + stable-queue as of commit afa3d2e7536e9034a4917d4b6e228a99d5bd7aa6 on my ThinkPad T14 Gen 1. I can no longer reproduce this kernel warning (as expected with the patches being dropped for now), and it's working well, and I have not observed any other regressions. Tested-by: Barry K. Nathan -- -Barry K. Nathan