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Thu, 02 Apr 2026 02:31:27 -0700 (PDT) Received: from [192.168.88.32] ([212.105.153.248]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-43d1e4d29bbsm6765274f8f.21.2026.04.02.02.31.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 02 Apr 2026 02:31:27 -0700 (PDT) Message-ID: <88deb91b-ef1b-403c-8eeb-0f971f27e34f@redhat.com> Date: Thu, 2 Apr 2026 11:31:26 +0200 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [REGRESSION] net: add xmit recursion limit to tunnel xmit functions To: Jakub Kicinski , Chris Arges Cc: Weiming Shi , Eric Dumazet , netdev@vger.kernel.org, kernel-team@cloudflare.com, jgriege@cloudflare.com References: <20260401173843.7a2bb607@kernel.org> Content-Language: en-US From: Paolo Abeni In-Reply-To: <20260401173843.7a2bb607@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/2/26 2:38 AM, Jakub Kicinski wrote: > On Tue, 31 Mar 2026 15:09:33 -0500 Chris Arges wrote: >> Commit 6f1a9140ecda ("net: add xmit recursion limit to tunnel xmit functions") >> introduces a regression in our systems using legitimate multi-level tunnel >> encapsulation stacks. Our testing was with stable 6.12.y and 6.18.y where this >> patch was backported. >> >> One of the usecases we have are packets being sent to a GRE device, then >> MPLS/LWT route, then IPIP device, then SIT/FOU device. What we observed is that >> packets are getting dropped at the last device and we get the message "Dead >> loop on virtual device" sent from the iptunnel_xmit function. > > Last device meaning limit of 5 would have worked for you? > I don't think there was any hard math behind the 4 so ++ > on the limit may be simplest, but I defer to Paolo.. AFAICS the '4' limit was an empirical choice, and the reported splat used 7 devices, so moving to 5 should fit, even if I must admit it feels a bit a whack a mole situation. On the flip side a revert of the blamed commit feels not safe. @Chris, could you please share a patch increasing the limit to 5? Thanks, Paolo