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 BC345C43334 for ; Tue, 14 Jun 2022 02:04:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234171AbiFNCEY (ORCPT ); Mon, 13 Jun 2022 22:04:24 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41108 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229633AbiFNCES (ORCPT ); Mon, 13 Jun 2022 22:04:18 -0400 Received: from out30-56.freemail.mail.aliyun.com (out30-56.freemail.mail.aliyun.com [115.124.30.56]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 138B530552; Mon, 13 Jun 2022 19:04:12 -0700 (PDT) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R191e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018046060;MF=xianting.tian@linux.alibaba.com;NM=1;PH=DS;RN=10;SR=0;TI=SMTPD_---0VGKvHPB_1655172248; Received: from B-LB6YLVDL-0141.local(mailfrom:xianting.tian@linux.alibaba.com fp:SMTPD_---0VGKvHPB_1655172248) by smtp.aliyun-inc.com; Tue, 14 Jun 2022 10:04:09 +0800 Subject: Re: [RESEND PATCH] mm: page_alloc: validate buddy before check the migratetype To: Guo Ren Cc: Andrew Morton , Vlastimil Babka , ziy@nvidia.com, Linux-MM , Linux Kernel Mailing List , stable@vger.kernel.org, huanyi.xj@alibaba-inc.com, zjb194813@alibaba-inc.com, tianhu.hh@alibaba-inc.com References: <20220613131046.3009889-1-xianting.tian@linux.alibaba.com> From: Xianting Tian Message-ID: Date: Tue, 14 Jun 2022 10:04:08 +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 2022/6/14 上午12:08, Guo Ren 写道: > On Mon, Jun 13, 2022 at 9:11 PM Xianting Tian > wrote: >> Commit 787af64d05cd ("mm: page_alloc: validate buddy before check its migratetype.") >> added buddy check code. But unfortunately, this fix isn't backported to >> linux-5.17.y and the former stable branches. The reason is it added wrong >> fixes message: >> Fixes: 1dd214b8f21c ("mm: page_alloc: avoid merging non-fallbackable >> pageblocks with others") >> Actually, this issue is involved by commit: >> commit d9dddbf55667 ("mm/page_alloc: prevent merging between isolated and other pageblocks") >> >> For RISC-V arch, the first 2M is reserved for sbi, so the start PFN is 512, >> but it got buddy PFN 0 for PFN 0x2000: >> 0 = 0x2000 ^ (1 << 12) > How did we get 0? （Try it in gdb) > (gdb) p /x (0x2000 ^ (1<<12)) > $3 = 0x3000 > > I think it got buddy PFN 0 for PFN 0x1000, right? > (gdb) p /x (0x1000 ^ (1<<12)) > $4 = 0x0 Sorry, it is a typo, the order is 0xd = 13, not 12. >> With the illegal buddy PFN 0, it got an illegal buddy page, which caused >> crash in __get_pfnblock_flags_mask(). >> >> With the patch, it can avoid the calling of get_pageblock_migratetype() if >> it isn't buddy page. >> >> 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/page_alloc.c | 3 +++ >> 1 file changed, 3 insertions(+) >> >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >> index b1caa1c6c887..5b423caa68fd 100644 >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -1129,6 +1129,9 @@ static inline void __free_one_page(struct page *page, >> >> buddy_pfn = __find_buddy_pfn(pfn, order); >> buddy = page + (buddy_pfn - pfn); >> + >> + if (!page_is_buddy(page, buddy, order)) > Right, we need to check the buddy_pfn valid, because some SoCs would > start dram address with an offset that has an order smaller than > MAX_ORDER. > >> + goto done_merging; >> buddy_mt = get_pageblock_migratetype(buddy); >> >> if (migratetype != buddy_mt >> -- >> 2.17.1 >> > Fixup the comment and > > Reviewed-by: Guo Ren >