From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-yw1-f172.google.com (mail-yw1-f172.google.com [209.85.128.172]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1620C17B05F; Tue, 9 Jul 2024 21:30:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720560603; cv=none; b=anp6mkBMYVGuvSKh0yCHbDB89/HovgvfZCmYZ1jG7YEskVtWgDrVUCzh1YUTvymxkZGUUdF0OI8Z/qPVKlMxQDrxwPqV0Xb0d1gSnxtAAIK0/OpUU9tsDdky0J3hxBwTPuo+R1h9was+TVox63SWwWVNv/3g9LP3ytXTRwL69G8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720560603; c=relaxed/simple; bh=NwcHMJbDrE9soGYhklNbRSR1jDwfxWXbqa6zKAsFC2o=; h=Date:From:To:Cc:Message-ID:In-Reply-To:References:Subject: Mime-Version:Content-Type; b=baOyjCg25qydGzPjATyLdlv8RwEEn5Gb8fG/uiQiHvZsux8UzSRk6IkdqxD5mGzfKaQSqhWWNW/SveagjfIn3epURnTk7JpRzQCuRcTW3SJrH+yqSFPJVsbRgKCQZI7oKjg7rj8dt4DGO9yfpXudTFbQJJSji5g4nYOfgx3Gq9M= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=R0hnsDq7; arc=none smtp.client-ip=209.85.128.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="R0hnsDq7" Received: by mail-yw1-f172.google.com with SMTP id 00721157ae682-64f4fb6ce65so48133477b3.2; Tue, 09 Jul 2024 14:30:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1720560601; x=1721165401; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:subject:references :in-reply-to:message-id:cc:to:from:date:from:to:cc:subject:date :message-id:reply-to; bh=mKz3aaHbTh5s5ue20BmsZpd/R0LLlhTOaVxDAJ/1Gog=; b=R0hnsDq7O85DB6i2JOC6YPfvi3Hlqbd55STv3C2tYzxtF+5BE0HifScY6X5MBzx6CH XMFLWDZwYlLbVaGFg+kDSntpyBH/X1eJHELANCI6fBpAkFFtkSQDSi6k0VPIGBR9TiPU Dj0yYgACe0Zh3Y2AL87qFxIoeR/cXQn/lVKCoZARxeg2+vCAjW6G61+YsbT8zzaOUCUU NCbw95HXk9dvv5y1Bb/xNf3uYF+bwRZ7GTqW6IzoowrVeZaaWUqZQSivlpyVhvN6tIhE LhYuwcDifKyfy62a7QXxSR3oD69VvXSa7Zr5lgeSsKx33iYzT+n6TNEmyjiweBQfkGqi 9dng== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1720560601; x=1721165401; h=content-transfer-encoding:mime-version:subject:references :in-reply-to:message-id:cc:to:from:date:x-gm-message-state:from:to :cc:subject:date:message-id:reply-to; bh=mKz3aaHbTh5s5ue20BmsZpd/R0LLlhTOaVxDAJ/1Gog=; b=Mgoer/gSSTBS908J51vhErNBjg5he/HWdNRX3iVWIyBhtvz68RGry7/WSoYk3YhUV9 JCwb4XfY5UzSaEtT6Rrb/HXEAx3aUyn1NoGv322W9ZQcJuYfdd2ebY4sDXRXqPPWJkb3 MI5klNHKYIv72s18caiKzZiULahkVufAcLVZzZ5CLjp9TMU5tbRx3eeTku1GwFSWkGsy OZ6uo5HcWC4c/CnXuok6gvr5nXsbLI365st3DfGRgLza3zVoNPFQwB+qHmg2B+yi+20a vxaYvJpUF8vIvjUIWEN1JvsQJO5GIkdS2WsML8aMlE/bF+EeqpP11nsfpsO9cG1MUlWd TD2g== X-Forwarded-Encrypted: i=1; AJvYcCXvIs1AsnqtbIdvAYxNlyvCgKvSZ25BmY8tQbLB9RbnJTgV4rm14dbIqFhedIbleeVcCLr0cwpoxaD4jPvyHx9ji2MaELTVLP3n/y9LkE+rn/7DkuK6Q+Rr215t/xhw7xtRHPTZ9qQKUlJCIhrvxcPqoREqgdEYtp84 X-Gm-Message-State: AOJu0YzXf7hHwTAe4BCDAH6GUPnJ9QPhPgKRHNe8N6aBu4k2z8eYamRC /Y1IKj6ZcoqgYgIZ00SLwb9uqsCcQIZegattdg5BxZMRha0y0DVq X-Google-Smtp-Source: AGHT+IHPgmrIrWc+akDsVCRw/o70dfEXyctNlGAFU6XNW8HLCynReHCIx9+9XFyceGpSaMFMYRXL+g== X-Received: by 2002:a81:770a:0:b0:62c:fcba:cfeb with SMTP id 00721157ae682-658f02f5e93mr42238597b3.34.1720560600845; Tue, 09 Jul 2024 14:30:00 -0700 (PDT) Received: from localhost (240.157.150.34.bc.googleusercontent.com. [34.150.157.240]) by smtp.gmail.com with ESMTPSA id af79cd13be357-79f1908ae8csm134094785a.88.2024.07.09.14.30.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 09 Jul 2024 14:30:00 -0700 (PDT) Date: Tue, 09 Jul 2024 17:29:59 -0400 From: Willem de Bruijn To: Herbert Xu , Willem de Bruijn Cc: Fred Li , aleksander.lobakin@intel.com, andrii@kernel.org, ast@kernel.org, bpf@vger.kernel.org, daniel@iogearbox.net, davem@davemloft.net, edumazet@google.com, haoluo@google.com, hawk@kernel.org, john.fastabend@gmail.com, jolsa@kernel.org, kpsingh@kernel.org, kuba@kernel.org, linux-kernel@vger.kernel.org, linux@weissschuh.net, martin.lau@linux.dev, mkhalfella@purestorage.com, nbd@nbd.name, netdev@vger.kernel.org, pabeni@redhat.com, sashal@kernel.org, sdf@google.com, song@kernel.org, yonghong.song@linux.dev Message-ID: <668dabd7e7066_1ce27f29435@willemb.c.googlers.com.notmuch> In-Reply-To: References: <6689541517901_12869e29412@willemb.c.googlers.com.notmuch> <20240708143128.49949-1-dracodingfly@gmail.com> <668d5cf1ec330_1c18c32947@willemb.c.googlers.com.notmuch> Subject: Re: [PATCH] net: linearizing skb when downgrade gso_size Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Herbert Xu wrote: > On Tue, Jul 09, 2024 at 11:53:21AM -0400, Willem de Bruijn wrote: > > > > > + /* Due to header grow, MSS needs to be downgraded. > > > + * There is BUG_ON When segment the frag_list with > > > + * head_frag true so linearize skb after downgrade > > > + * the MSS. > > > + */ > > This sounds completely wrong. You should never grow the TCP header > by changing gso_size. What is the usage-scenario for this? > > Think about it, if a router forwards a TCP packet, and ends up > growing its TCP header and then splits the packet into two, then > this router is brain-dead. This is an unfortunate feature, but already exists. It decreases gso_size to account for tunnel headers. For USO, we added BPF_F_ADJ_ROOM_FIXED_GSO to avoid this in better, newer users.