From patchwork Tue Feb 4 23:41:06 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: John Hubbard X-Patchwork-Id: 11365461 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 8B2F392A for ; Tue, 4 Feb 2020 23:42:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 683CC21582 for ; Tue, 4 Feb 2020 23:42:24 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=nvidia.com header.i=@nvidia.com header.b="ICEnL1/j" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727693AbgBDXlV (ORCPT ); Tue, 4 Feb 2020 18:41:21 -0500 Received: from hqnvemgate26.nvidia.com ([216.228.121.65]:4032 "EHLO hqnvemgate26.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727483AbgBDXlU (ORCPT ); Tue, 4 Feb 2020 18:41:20 -0500 Received: from hqpgpgate102.nvidia.com (Not Verified[216.228.121.13]) by hqnvemgate26.nvidia.com (using TLS: TLSv1.2, DES-CBC3-SHA) id ; Tue, 04 Feb 2020 15:41:05 -0800 Received: from hqmail.nvidia.com ([172.20.161.6]) by hqpgpgate102.nvidia.com (PGP Universal service); Tue, 04 Feb 2020 15:41:20 -0800 X-PGP-Universal: processed; by hqpgpgate102.nvidia.com on Tue, 04 Feb 2020 15:41:20 -0800 Received: from HQMAIL111.nvidia.com (172.20.187.18) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Tue, 4 Feb 2020 23:41:19 +0000 Received: from rnnvemgw01.nvidia.com (10.128.109.123) by HQMAIL111.nvidia.com (172.20.187.18) with Microsoft SMTP Server (TLS) id 15.0.1473.3 via Frontend Transport; Tue, 4 Feb 2020 23:41:19 +0000 Received: from blueforge.nvidia.com (Not Verified[10.110.48.28]) by rnnvemgw01.nvidia.com with Trustwave SEG (v7,5,8,10121) id ; Tue, 04 Feb 2020 15:41:18 -0800 From: John Hubbard To: Andrew Morton CC: Al Viro , Christoph Hellwig , Dan Williams , Dave Chinner , Ira Weiny , Jan Kara , Jason Gunthorpe , Jonathan Corbet , =?utf-8?b?SsOpcsO0bWUgR2xpc3Nl?= , "Kirill A . Shutemov" , Michal Hocko , Mike Kravetz , Shuah Khan , Vlastimil Babka , Matthew Wilcox , , , , , , LKML , John Hubbard , "Kirill A . Shutemov" Subject: [PATCH v4 01/12] mm: dump_page(): better diagnostics for compound pages Date: Tue, 4 Feb 2020 15:41:06 -0800 Message-ID: <20200204234117.2974687-2-jhubbard@nvidia.com> X-Mailer: git-send-email 2.25.0 In-Reply-To: <20200204234117.2974687-1-jhubbard@nvidia.com> References: <20200204234117.2974687-1-jhubbard@nvidia.com> MIME-Version: 1.0 X-NVConfidentiality: public DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1580859665; bh=JHbFoVlby1O2Fi0YWtwHfwC9UdnPi6RlItOvHznb5y0=; h=X-PGP-Universal:From:To:CC:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:X-NVConfidentiality: Content-Transfer-Encoding:Content-Type; b=ICEnL1/jGgV4z6oz1HWOx8M2NHn7cYSc3TxlKz7MH+gGFMc4B+A8SY56czLlzC1k9 Oos3chmRpBNNkWgFSee9Gt+C0TdJH9XnDS3MxUWnZWfpYuOGdWg9seyEHAVddiQQ+J WUp+2meTAUfwrE3rIkDYIxdb5y4oF7qPwacm/76itNUnjmfR88jwh7uiK5wPTomvIB 8FFFVEfjucP2JbgO1qF+fudS88NVp9kZFQM944vOB8w5+1uYO8s00kYZCsDcLV1nX7 FB7UzmfIkTFAKoknI+Yc8Ky9EaPshAQxhfkPzBrNeJte11ZT3KRd337JkHQwYuIBYw eWEU9Ffle2DQg== Sender: linux-kselftest-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org A compound page collects the refcount in the head page, while leaving the refcount of each tail page at zero. Therefore, when debugging a problem that involves compound pages, it's best to have diagnostics that reflect that situation. However, dump_page() is oblivious to these points. Change dump_page() as follows: 1) For tail pages, print relevant head page information: refcount, in particular. But only do this if the page is not corrupted so badly that the pointer to the head page is all wrong. 2) Do a separate check to catch any (rare) cases of the tail page's refcount being non-zero, and issue a separate, clear pr_warn() if that ever happens. Suggested-by: Matthew Wilcox Suggested-by: Kirill A. Shutemov Acked-by: Kirill A. Shutemov Signed-off-by: John Hubbard --- mm/debug.c | 35 +++++++++++++++++++++++++++++------ 1 file changed, 29 insertions(+), 6 deletions(-) diff --git a/mm/debug.c b/mm/debug.c index ecccd9f17801..f074077eee11 100644 --- a/mm/debug.c +++ b/mm/debug.c @@ -42,6 +42,33 @@ const struct trace_print_flags vmaflag_names[] = { {0, NULL} }; +static void __dump_tail_page(struct page *page, int mapcount) +{ + 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)); + } +} + void __dump_page(struct page *page, const char *reason) { struct address_space *mapping; @@ -75,12 +102,8 @@ 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)) + __dump_tail_page(page, mapcount); else pr_warn("page:%px refcount:%d mapcount:%d mapping:%px index:%#lx\n", page, page_ref_count(page), mapcount,