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Mon, 07 Sep 2026 21:31:45 -0700 (PDT) From: AnishMulay To: idosch@nvidia.com Cc: pimyn@google.com, dsahern@kernel.org, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, syzbot+ded267b328e950a7c0c4@syzkaller.appspotmail.com Subject: Re: [PATCH] ipv6: addrconf: drop "BUG: " prefix from pr_warn() Date: Tue, 8 Sep 2026 00:31:43 -0400 Message-ID: <20260908043143.120335-1-anishm7030@gmail.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260810103517.GA2626301@shredder> References: <20260807131300.2677228-1-pimyn@google.com> <20260810095136.GA2582170@shredder> <20260810103517.GA2626301@shredder> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Hi Ido, I ran into this same warning independently (different syzbot report, address 2001::fb rather than fc00::, extid 57f410c9a4f8d7a441d6) and ended up tracing it down before finding this thread. The mechanism in my case: keep_addr_on_down is set, addrconf_ifdown() clears ifp->rt and deletes the route for the kept address but skips its notifier. On the following up, fixup_permanent_addr() allocates a new fib6_info and schedules addrconf_dad_work asynchronously instead of inserting the route itself. If a second addrconf_ifdown() for the same device runs before that work item gets to execute (I see this happen within a single "ip link set lo up" call, which drives both a NETDEV_UP and a NETDEV_CHANGE through addrconf_notify()), the fresh route gets torn down again with no notifier to re-arm anything. The work item then runs with ifp->rt NULL and nothing left to insert. I have a patch that regenerates the route at that point instead of only warning, verified against a C reproducer translated from the syzbot repro (no warning, and the /128 route is present after the down/up cycle, across repeated runs). Since you mentioned you were looking into avoiding this state, I wanted to check before sending it, in case you already have something further along or a different angle on it. Happy to send what I have either way. Anish