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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 470A5C433EF for ; Wed, 22 Jun 2022 01:37:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1355612AbiFVBhT (ORCPT ); Tue, 21 Jun 2022 21:37:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47144 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233157AbiFVBhR (ORCPT ); Tue, 21 Jun 2022 21:37:17 -0400 Received: from out199-3.us.a.mail.aliyun.com (out199-3.us.a.mail.aliyun.com [47.90.199.3]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 74C5BFD16; Tue, 21 Jun 2022 18:37:13 -0700 (PDT) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R201e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018045168;MF=xianting.tian@linux.alibaba.com;NM=1;PH=DS;RN=11;SR=0;TI=SMTPD_---0VH3NzQv_1655861827; Received: from B-LB6YLVDL-0141.local(mailfrom:xianting.tian@linux.alibaba.com fp:SMTPD_---0VH3NzQv_1655861827) by smtp.aliyun-inc.com; Wed, 22 Jun 2022 09:37:08 +0800 Subject: Re: [PATCH 5.15] mm: validate buddy page before using To: Greg KH , Zi Yan Cc: akpm@linux-foundation.org, stable@vger.kernel.org, guoren@kernel.org, huanyi.xj@alibaba-inc.com, guohanjun@huawei.com, zjb194813@alibaba-inc.com, tianhu.hh@alibaba-inc.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <35bd7396-f5aa-e154-9495-0a36fc6f6a33@linux.alibaba.com> <8b16a502-5ad5-1efb-0d84-ed0a8ae63c0e@linux.alibaba.com> <3371C275-E45D-445F-838E-D43C60BCD750@nvidia.com> <62DC5603-F88E-40A3-A4AD-EEFA7027C399@nvidia.com> From: Xianting Tian Message-ID: <249cf3e9-4a4f-5258-5d55-6c90f0137496@linux.alibaba.com> Date: Wed, 22 Jun 2022 09:37:06 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 在 2022/6/21 上午4:31, Greg KH 写道: > On Mon, Jun 20, 2022 at 10:13:59AM -0400, Zi Yan wrote: >> On 20 Jun 2022, at 8:54, Greg KH wrote: >> >>> On Mon, Jun 20, 2022 at 08:45:13AM -0400, Zi Yan wrote: >>>> On 20 Jun 2022, at 8:24, Greg KH wrote: >>>> >>>>> On Mon, Jun 20, 2022 at 08:18:40PM +0800, Xianting Tian wrote: >>>>>> 在 2022/6/20 下午8:06, Greg KH 写道: >>>>>>> On Mon, Jun 20, 2022 at 07:57:05PM +0800, Xianting Tian wrote: >>>>>>>> 在 2022/6/20 下午7:42, Greg KH 写道: >>>>>>>>> On Mon, Jun 20, 2022 at 06:54:44PM +0800, Xianting Tian wrote: >>>>>>>>>> 在 2022/6/20 下午6:17, Greg KH 写道: >>>>>>>>>>> On Fri, Jun 17, 2022 at 12:17:45AM +0800, Xianting Tian wrote: >>>>>>>>>>>> Commit 787af64d05cd ("mm: page_alloc: validate buddy before check its migratetype.") >>>>>>>>>>>> fixes a bug in 1dd214b8f21c and there is a similar bug in d9dddbf55667 that >>>>>>>>>>>> can be fixed in a similar way too. >>>>>>>>>>>> >>>>>>>>>>>> In unset_migratetype_isolate(), we also need the fix, so move page_is_buddy() >>>>>>>>>>>> from mm/page_alloc.c to mm/internal.h >>>>>>>>>>>> >>>>>>>>>>>> In addition, for RISC-V arch the first 2MB RAM could be reserved for opensbi, >>>>>>>>>>>> so it would have pfn_base=512 and mem_map began with 512th PFN when >>>>>>>>>>>> CONFIG_FLATMEM=y. >>>>>>>>>>>> But __find_buddy_pfn algorithm thinks the start pfn 0, it could get 0 pfn or >>>>>>>>>>>> less than the pfn_base value. We need page_is_buddy() to verify the buddy to >>>>>>>>>>>> prevent accessing an invalid buddy. >>>>>>>>>>>> >>>>>>>>>>>> Fixes: d9dddbf55667 ("mm/page_alloc: prevent merging between isolated and other pageblocks") >>>>>>>>>>>> Cc: stable@vger.kernel.org >>>>>>>>>>>> Reported-by: zjb194813@alibaba-inc.com >>>>>>>>>>>> Reported-by: tianhu.hh@alibaba-inc.com >>>>>>>>>>>> Signed-off-by: Xianting Tian >>>>>>>>>>>> --- >>>>>>>>>>>> mm/internal.h | 34 ++++++++++++++++++++++++++++++++++ >>>>>>>>>>>> mm/page_alloc.c | 37 +++---------------------------------- >>>>>>>>>>>> mm/page_isolation.c | 3 ++- >>>>>>>>>>>> 3 files changed, 39 insertions(+), 35 deletions(-) >>>>>>>>>>> What is the commit id of this in Linus's tree? >>>>>>>>>> It is also this one， >>>>>>>>>> >>>>>>>>>> commit 787af64d05cd528aac9ad16752d11bb1c6061bb9 >>>>>>>>>> Author: Zi Yan >>>>>>>>>> Date:   Wed Mar 30 15:45:43 2022 -0700 >>>>>>>>>> >>>>>>>>>>     mm: page_alloc: validate buddy before check its migratetype. >>>>>>>>>> >>>>>>>>>>     Whenever a buddy page is found, page_is_buddy() should be called to >>>>>>>>>>     check its validity.  Add the missing check during pageblock merge check. >>>>>>>>>> >>>>>>>>>>     Fixes: 1dd214b8f21c ("mm: page_alloc: avoid merging non-fallbackable >>>>>>>>>> pageblocks with others") >>>>>>>>>>     Link: >>>>>>>>>> https://lore.kernel.org/all/20220330154208.71aca532@gandalf.local.home/ >>>>>>>>>>     Reported-and-tested-by: Steven Rostedt >>>>>>>>>>     Signed-off-by: Zi Yan >>>>>>>>>>     Signed-off-by: Linus Torvalds >>>>>>>>> This commit looks nothing like what you posted here. >>>>>>>>> >>>>>>>>> Why the vast difference with no explaination as to why these are so >>>>>>>>> different from the other backports you provided here? Also why is the >>>>>>>>> subject lines changed? >>>>>>>> Yes, the changes of 5.15 are not same with others branches, because we need >>>>>>>> additional fix for 5.15, >>>>>>>> >>>>>>>> You can check it in the thread: >>>>>>>> >>>>>>>> https://lore.kernel.org/linux-mm/435B45C3-E6A5-43B2-A5A2-318C748691FC@nvidia.com/ >>>>>>>> >>>>>>>> Right. But pfn_valid_within() was removed since 5.15. So your fix is >>>>>>>> required for kernels between 5.15 and 5.17 (inclusive). >>>>>>> What is "your fix" here? >>>>>>> >>>>>>> This change differs a lot from what is in Linus's tree now, so this all >>>>>>> needs to be resend and fixed up as I mention above if we are going to be >>>>>>> able to take this. As-is, it's all not correct so are dropped. >>>>>> I think, for branches except 5.15,  you can just backport Zi Yan's commit >>>>>> 787af64d05cd in Linus tree. I won't send more patches further, >>>>> So just for 5.18? I am confused. >>>>> >>>>>> For 5.15, because it need additional fix except commit 787af64d05cd,  I will >>>>>> send a new patch as your comments. >>>>>> >>>>>> Is it ok for you? >>>>> No, please send fixed up patches for all branches you want them applied >>>>> to as I do not understand what to do here at all, sorry. >>>> Hi Greg, >>>> >>>> The fixes sent by Xianting do not exist in Linus’s tree, since the bug is >>>> fixed by another commit, which was not intended to fix the bug from the commit >>>> d9dddbf55667. These fixes only target the stable branches. >>> Then that all needs to be documented very very very well as to why we >>> can't just take the commit that is in Linus's tree. >>> >>> Why can't we take that commit instead? >> The situation is a little complicated. >> >> The bug from commit d9dddbf55667 was not discovered back then. The commit 1dd214b8f21c >> was trying to get migratetype merging more rigid and made the bug easy to get >> hit, but none of us were aware of that the bug also exists in commit d9dddbf55667. >> Then the commit 787af64d05cd fixed the bug, but since the original code was >> changed by commit 1dd214b8f21c, thus, it does not directly apply to >> commit d9dddbf55667. So I do not think it makes sense to use the original commits >> 1dd214b8f21c and 787af64d05cd, since the former makes a non bug fixing change and >> the latter fixes the bug revealed by the former. > That is exactly what we want to apply, we almost never want to apply > stuff that is not upstream. When we do apply "custom" patches, they are > almost always wrong. We have a long history of this, please let's just > take the originals please. > >> As a result, Xianting's patches fix the bug directly, looking more reasonable to me. > Again, please no, let's take the originals and keep in step with what is > in Linus's tree which makes maintance and tracking and everything so > much easier over time. If so, I think we only can backport 787af64d from Linus tree to all stable branches. Our ultimate purpose is to solve the problem, I think @Zi Yan will agree? > > thanks, > > greg k-h