From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 009BFC47095 for ; Sun, 4 Oct 2020 22:15:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C4B8A20678 for ; Sun, 4 Oct 2020 22:15:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726831AbgJDWPk (ORCPT ); Sun, 4 Oct 2020 18:15:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58820 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726616AbgJDWPi (ORCPT ); Sun, 4 Oct 2020 18:15:38 -0400 Received: from shards.monkeyblade.net (shards.monkeyblade.net [IPv6:2620:137:e000::1:9]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 38F06C0613CE; Sun, 4 Oct 2020 15:15:38 -0700 (PDT) Received: from localhost (unknown [IPv6:2601:601:9f00:477::3d5]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) (Authenticated sender: davem-davemloft) by shards.monkeyblade.net (Postfix) with ESMTPSA id E377212784833; Sun, 4 Oct 2020 14:58:49 -0700 (PDT) Date: Sun, 04 Oct 2020 15:15:35 -0700 (PDT) Message-Id: <20201004.151535.2244486201194283232.davem@davemloft.net> To: xie.he.0141@gmail.com Cc: kuba@kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, willemdebruijn.kernel@gmail.com, ms@dev.tdt.de Subject: Re: [PATCH net] drivers/net/wan: lapb: Replace the skb->len checks with pskb_may_pull From: David Miller In-Reply-To: <20201004004619.291065-1-xie.he.0141@gmail.com> References: <20201004004619.291065-1-xie.he.0141@gmail.com> X-Mailer: Mew version 6.8 on Emacs 27.1 Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.5.12 (shards.monkeyblade.net [2620:137:e000::1:9]); Sun, 04 Oct 2020 14:58:50 -0700 (PDT) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Xie He Date: Sat, 3 Oct 2020 17:46:19 -0700 > The purpose of these skb->len checks in these drivers is to ensure that > there is a header in the skb available to be read and pulled. > > However, we already have the pskb_may_pull function for this purpose. > > The pskb_may_pull function also correctly handles non-linear skbs. > > (Also delete the word "check" in the comments because pskb_may_pull may > do things other than simple checks in the case of non-linear skbs.) > > Cc: Willem de Bruijn > Cc: Martin Schiller > Signed-off-by: Xie He This is excessive. On transmit the header will be in the linear area, especially if it is only one byte in size. You're adding a lot of extra checks, function calls, etc. which are frankly unnecessary. I'm not applying this unless you can prove that a non-linear single header byte is possible in these code paths. And you'll need to add such proof to your commit message. Thank you.