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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 09EC9C433DF for ; Mon, 17 Aug 2020 05:45:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DE90420855 for ; Mon, 17 Aug 2020 05:45:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726706AbgHQFpn (ORCPT ); Mon, 17 Aug 2020 01:45:43 -0400 Received: from verein.lst.de ([213.95.11.211]:55031 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726303AbgHQFpm (ORCPT ); Mon, 17 Aug 2020 01:45:42 -0400 Received: by verein.lst.de (Postfix, from userid 2407) id 69E1767357; Mon, 17 Aug 2020 07:45:38 +0200 (CEST) Date: Mon, 17 Aug 2020 07:45:38 +0200 From: Christoph Hellwig To: Cong Wang Cc: Coly Li , linux-block@vger.kernel.org, linux-nvme@lists.infradead.org, Linux Kernel Network Developers , stable , LKML , Chaitanya Kulkarni , Christoph Hellwig , Hannes Reinecke , Jan Kara , Jens Axboe , Mikhail Skorzhinskii , Philipp Reisner , Sagi Grimberg , Vlastimil Babka Subject: Re: [PATCH v5 1/3] net: introduce helper sendpage_ok() in include/linux/net.h Message-ID: <20200817054538.GA11705@lst.de> References: <20200816071518.6964-1-colyli@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Aug 16, 2020 at 10:55:09AM -0700, Cong Wang wrote: > On Sun, Aug 16, 2020 at 1:36 AM Coly Li wrote: > > > > The original problem was from nvme-over-tcp code, who mistakenly uses > > kernel_sendpage() to send pages allocated by __get_free_pages() without > > __GFP_COMP flag. Such pages don't have refcount (page_count is 0) on > > tail pages, sending them by kernel_sendpage() may trigger a kernel panic > > from a corrupted kernel heap, because these pages are incorrectly freed > > in network stack as page_count 0 pages. > > > > This patch introduces a helper sendpage_ok(), it returns true if the > > checking page, > > - is not slab page: PageSlab(page) is false. > > - has page refcount: page_count(page) is not zero > > > > All drivers who want to send page to remote end by kernel_sendpage() > > may use this helper to check whether the page is OK. If the helper does > > not return true, the driver should try other non sendpage method (e.g. > > sock_no_sendpage()) to handle the page. > > Can we leave this helper to mm subsystem? > > I know it is for sendpage, but its implementation is all about some > mm details and its two callers do not belong to net subsystem either. > > Think this in another way: who would fix it if it is buggy? I bet mm people > should. ;) No. This is all about a really unusual imitation in sendpage, which is pretty much unexpected. In fact the best thing would be to make sock_sendpage do the right thing and call sock_no_sendpage based on this condition, so that driver writers don't have to worry at all.