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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH net] amt: do not offer software GSO on the amt device Date: Thu, 1 Oct 2026 01:26:51 +0300 Message-ID: <20260930222700.45470-1-omar@blockcast.net> X-Mailer: git-send-email 2.50.1 In-Reply-To: <179061959167.31693.11895969550331516671@kernel.org> References: <20260928181554.85766-1-omar@blockcast.net> <179061959167.31693.11895969550331516671@kernel.org> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Found by code inspection: an LLM-assisted review of drivers/net/amt.c while I was working on an IPv6 outer transport for amt. It has not been triggered. I have no reproducer, and I have not seen it in production or in testing; it comes from reading the code. The path is a GSO skb, for example from a UDP_SEGMENT sender or a GRO merged UDP flow, that is routed to a relay's amt device: it reaches amt_dev_xmit() unsegmented because the device offers NETIF_F_GSO_SOFTWARE, and the outer UDP layer later segments each per-tunnel copy at the inner gso_size. Testing: W=1 build with CONFIG_IPV6=y and =n, and tools/testing/selftests/net/amt.sh passes with the patch applied, but amt.sh never sends a GSO skb, so nothing exercises the changed path.