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=-5.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 63003C35240 for ; Thu, 30 Jan 2020 06:26:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 353A82083E for ; Thu, 30 Jan 2020 06:26:24 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=nvidia.com header.i=@nvidia.com header.b="BQDWkRnL" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725865AbgA3G0N (ORCPT ); Thu, 30 Jan 2020 01:26:13 -0500 Received: from hqnvemgate24.nvidia.com ([216.228.121.143]:17654 "EHLO hqnvemgate24.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725798AbgA3G0N (ORCPT ); Thu, 30 Jan 2020 01:26:13 -0500 Received: from hqpgpgate102.nvidia.com (Not Verified[216.228.121.13]) by hqnvemgate24.nvidia.com (using TLS: TLSv1.2, DES-CBC3-SHA) id ; Wed, 29 Jan 2020 22:25:19 -0800 Received: from hqmail.nvidia.com ([172.20.161.6]) by hqpgpgate102.nvidia.com (PGP Universal service); Wed, 29 Jan 2020 22:26:11 -0800 X-PGP-Universal: processed; by hqpgpgate102.nvidia.com on Wed, 29 Jan 2020 22:26:11 -0800 Received: from [10.2.165.69] (10.124.1.5) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Thu, 30 Jan 2020 06:26:10 +0000 Subject: Re: [PATCH v2 1/8] mm: dump_page: print head page's refcount, for compound pages To: Matthew Wilcox CC: "Kirill A. Shutemov" , Andrew Morton , Al Viro , Christoph Hellwig , Dan Williams , Dave Chinner , Ira Weiny , Jan Kara , Jason Gunthorpe , Jonathan Corbet , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Michal Hocko , Mike Kravetz , Shuah Khan , Vlastimil Babka , , , , , , LKML References: <20200129032417.3085670-1-jhubbard@nvidia.com> <20200129032417.3085670-2-jhubbard@nvidia.com> <20200129112510.ulims6u36ofk2qwa@box> <20200129225957.GH6615@bombadil.infradead.org> From: John Hubbard X-Nvconfidentiality: public Message-ID: Date: Wed, 29 Jan 2020 22:23:10 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.2 MIME-Version: 1.0 In-Reply-To: <20200129225957.GH6615@bombadil.infradead.org> X-Originating-IP: [10.124.1.5] X-ClientProxiedBy: HQMAIL101.nvidia.com (172.20.187.10) To HQMAIL107.nvidia.com (172.20.187.13) Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1580365520; bh=JHRJR+nRNJ+fPdKgdhNh0UpV2gT6YF7QTq3XuI/pnwo=; h=X-PGP-Universal:Subject:To:CC:References:From:X-Nvconfidentiality: Message-ID:Date:User-Agent:MIME-Version:In-Reply-To: X-Originating-IP:X-ClientProxiedBy:Content-Type:Content-Language: Content-Transfer-Encoding; b=BQDWkRnLH1j0+3TFcqwPmncBEuhinrmCw80Gb5nfjCWCm7Q+eTszuPPxdRdT/9ncI x3vf//wCgavyZ2zurvNKovAxI/vZkKZclk357DNkl6D/x0aJAzNgqEhRFJp40iDBED blM/4jKRxhuyVU/WLFsXsLkxawG9WIwlVDfIJ1gmdL52WG4s3jP21Q+xONM74akxo2 o3rwO1ZZPh/0w73Q2KfxYhHRtPrL4ctXCQQyM51KBuG20kGnsUbBy868Exg0yU1S/h uGFVs4y/C8Uwpoh/bi+N1dF2g3hx5+SVKe+Fwn5Npk5ECCkzzyiD+r1UvShA2fyeI4 td4jAMZ7SAJdw== Sender: linux-kselftest-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org On 1/29/20 2:59 PM, Matthew Wilcox wrote: ... > I have a hunk in my current tree which looks like this: > > @@ -77,6 +77,11 @@ void __dump_page(struct page *page, const char *reason) > pr_warn("page:%px refcount:%d mapcount:%d mapping:%px index:%#lx > \n", > page, page_ref_count(page), mapcount, > page->mapping, page_to_pgoff(page)); > + if (PageTail(page)) { > + struct page *head = compound_head(page); > + pr_warn("head:%px mapping:%px index:%#lx\n", > + head, head->mapping, page_to_pgoff(head)); > + } > if (PageKsm(page)) > pr_warn("ksm flags: %#lx(%pGp)\n", page->flags, &page->flags); > else if (PageAnon(page)) > > I wonder if we can combine these two patches in some more useful way? > > I also think we probably want a sanity check that 'head' and 'page' > are within a sane range of each other (ie head < page and head + > MAX_ORDER_NR_PAGES > page) to protect against a struct page that contains > complete garbage. > OK, here's a go at combining those. I like the observation, implicit in your diffs, that PageTail rather than PageCompound is the key differentiator in deciding what to print. How's this look: diff --git a/mm/debug.c b/mm/debug.c index a90da5337c14..944652843e7b 100644 --- a/mm/debug.c +++ b/mm/debug.c @@ -75,12 +75,31 @@ void __dump_page(struct page *page, const char *reason) */ mapcount = PageSlab(page) ? 0 : page_mapcount(page); - if (PageCompound(page)) - pr_warn("page:%px refcount:%d mapcount:%d mapping:%px " - "index:%#lx compound_mapcount: %d\n", - page, page_ref_count(page), mapcount, - page->mapping, page_to_pgoff(page), - compound_mapcount(page)); + if (PageTail(page)) { + struct page *head = compound_head(page); + + if ((page < head) || (page >= head + MAX_ORDER_NR_PAGES)) { + /* + * Page is hopelessly corrupted, so limit any reporting + * to information about the page itself. Do not attempt + * to look at the head page. + */ + pr_warn("page:%px refcount:%d mapcount:%d mapping:%px " + "index:%#lx (corrupted tail page case)\n", + page, page_ref_count(page), mapcount, + page->mapping, page_to_pgoff(page)); + } else { + pr_warn("page:%px compound refcount:%d mapcount:%d " + "mapping:%px index:%#lx compound_mapcount:%d\n", + page, page_ref_count(head), + mapcount, head->mapping, page_to_pgoff(head), + compound_mapcount(page)); + + if (page_ref_count(page) != 0) + pr_warn("page:%px PROBLEM: non-zero refcount (==%d) on " + "this tail page\n", page, page_ref_count(page)); + } + } else pr_warn("page:%px refcount:%d mapcount:%d mapping:%px index:%#lx\n", page, page_ref_count(page), mapcount, ? Here's sample output for a normal page, a tail page, and a tail page with a bad (non-zero) refcount: ============ Normal page: ============ [ 38.572084] page:ffffea0011465880 refcount:2 mapcount:1 mapping:ffff888454d99001 index:0xb2 [ 38.579256] anon flags: 0x17ffe0000080036(referenced|uptodate|lru|active|swapbacked) [ 38.585799] raw: 017ffe0000080036 ffffea0011460fc8 ffffea0011466d08 ffff888454d99001 [ 38.592350] raw: 00000000000000b2 0000000000000000 0000000200000000 0000000000000000 [ 38.598885] page dumped because: test dump page ========== Tail page: ========== [ 38.436384] page:ffffea0010aa0280 compound refcount:503 mapcount:1 mapping:ffff888455fb3399 index:0xa8 compound_mapcount:1 [ 38.446350] anon flags: 0x17ffe0000000000() [ 38.449661] raw: 017ffe0000000000 ffffea0010aa0001 ffffea0010aa0288 dead000000000400 [ 38.456228] raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000 [ 38.462794] page dumped because: test dump page ============================ Tail page with bad refcount: ============================ [ 38.466088] page:ffffea0010aa0b40 compound refcount:468 mapcount:1 mapping:ffff888455fb3399 index:0xa8 compound_mapcount:1 [ 38.475967] page:ffffea0010aa0b40 PROBLEM: non-zero refcount (==2) on this tail page [ 38.482490] anon flags: 0x17ffe0000000000() [ 38.485432] raw: 017ffe0000000000 ffffea0010aa0001 ffffea0010aa0b48 dead000000000400 [ 38.491996] raw: 0000000000000000 0000000000000000 00000002ffffffff 0000000000000000 [ 38.498532] page dumped because: test bad tail page refcount thanks, -- John Hubbard NVIDIA