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[146.241.226.170]) by smtp.gmail.com with ESMTPSA id n14-20020a0ce48e000000b0062b76c29978sm154802qvl.6.2023.07.20.00.18.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 20 Jul 2023 00:18:49 -0700 (PDT) Message-ID: Subject: Re: [syzbot] [btrfs?] [netfilter?] BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low! (2) From: Paolo Abeni To: Jakub Kicinski , netdev@vger.kernel.org Cc: Florian Westphal , Aleksandr Nogikh , syzbot , dsterba@suse.cz, bakmitopiacibubur@boga.indosterling.com, clm@fb.com, davem@davemloft.net, dsahern@kernel.org, dsterba@suse.com, gregkh@linuxfoundation.org, jirislaby@kernel.org, josef@toxicpanda.com, kadlec@netfilter.org, linux-btrfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, linux@armlinux.org.uk, netfilter-devel@vger.kernel.org, pablo@netfilter.org, syzkaller-bugs@googlegroups.com Date: Thu, 20 Jul 2023 09:18:44 +0200 In-Reply-To: <20230719203030.1296596a@kernel.org> References: <20230719170446.GR20457@twin.jikos.cz> <00000000000042a3ac0600da1f69@google.com> <20230719231207.GF32192@breakpoint.cc> <20230719203030.1296596a@kernel.org> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.46.4 (3.46.4-1.fc37) MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: netfilter-devel@vger.kernel.org On Wed, 2023-07-19 at 20:30 -0700, Jakub Kicinski wrote: > On Thu, 20 Jul 2023 01:12:07 +0200 Florian Westphal wrote: > > I don't see any netfilter involvement here. > >=20 > > The repro just creates a massive amount of team devices. > >=20 > > At the time it hits the LOCKDEP limits on my test vm it has > > created ~2k team devices, system load is at +14 because udev > > is also busy spawing hotplug scripts for the new devices. > >=20 > > After reboot and suspending the running reproducer after about 1500 > > devices (before hitting lockdep limits), followed by 'ip link del' for > > the team devices gets the lockdep entries down to ~8k (from 40k), > > which is in the range that it has on this VM after a fresh boot. > >=20 > > So as far as I can see this workload is just pushing lockdep > > past what it can handle with the configured settings and is > > not triggering any actual bug. >=20 > The lockdep splat because of netdevice stacking is one of our top > reports from syzbot. Is anyone else feeling like we should add=20 > an artificial but very high limit on netdev stacking? :( We already have a similar limit for xmit: XMIT_RECURSION_LIMIT. I guess stacking more then such devices will be quite useless/non functional. We could use such value to limit the device stacking, too. Cheers, Paolo