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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 089F4C31E40 for ; Tue, 6 Aug 2019 07:53:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D6A802070C for ; Tue, 6 Aug 2019 07:53:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732170AbfHFHxt (ORCPT ); Tue, 6 Aug 2019 03:53:49 -0400 Received: from mx2.suse.de ([195.135.220.15]:42958 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726834AbfHFHxs (ORCPT ); Tue, 6 Aug 2019 03:53:48 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 84A25AD29; Tue, 6 Aug 2019 07:53:47 +0000 (UTC) Subject: Re: [PATCH V2] fork: Improve error message for corrupted page tables To: Sai Praneeth Prakhya , linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: dave.hansen@intel.com, Ingo Molnar , Peter Zijlstra , Andrew Morton , Anshuman Khandual References: <3ef8a340deb1c87b725d44edb163073e2b6eca5a.1565059496.git.sai.praneeth.prakhya@intel.com> From: Vlastimil Babka Message-ID: <5ba88460-cf01-3d53-6d13-45e650b4eacd@suse.cz> Date: Tue, 6 Aug 2019 09:53:46 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <3ef8a340deb1c87b725d44edb163073e2b6eca5a.1565059496.git.sai.praneeth.prakhya@intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/6/19 5:05 AM, Sai Praneeth Prakhya wrote: > When a user process exits, the kernel cleans up the mm_struct of the user > process and during cleanup, check_mm() checks the page tables of the user > process for corruption (E.g: unexpected page flags set/cleared). For > corrupted page tables, the error message printed by check_mm() isn't very > clear as it prints the loop index instead of page table type (E.g: Resident > file mapping pages vs Resident shared memory pages). The loop index in > check_mm() is used to index rss_stat[] which represents individual memory > type stats. Hence, instead of printing index, print memory type, thereby > improving error message. > > Without patch: > -------------- > [ 204.836425] mm/pgtable-generic.c:29: bad p4d 0000000089eb4e92(800000025f941467) > [ 204.836544] BUG: Bad rss-counter state mm:00000000f75895ea idx:0 val:2 > [ 204.836615] BUG: Bad rss-counter state mm:00000000f75895ea idx:1 val:5 > [ 204.836685] BUG: non-zero pgtables_bytes on freeing mm: 20480 > > With patch: > ----------- > [ 69.815453] mm/pgtable-generic.c:29: bad p4d 0000000084653642(800000025ca37467) > [ 69.815872] BUG: Bad rss-counter state mm:00000000014a6c03 type:MM_FILEPAGES val:2 > [ 69.815962] BUG: Bad rss-counter state mm:00000000014a6c03 type:MM_ANONPAGES val:5 > [ 69.816050] BUG: non-zero pgtables_bytes on freeing mm: 20480 > > Also, change print function (from printk(KERN_ALERT, ..) to pr_alert()) so > that it matches the other print statement. > > Cc: Ingo Molnar > Cc: Vlastimil Babka > Cc: Peter Zijlstra > Cc: Andrew Morton > Cc: Anshuman Khandual > Acked-by: Dave Hansen > Suggested-by: Dave Hansen > Signed-off-by: Sai Praneeth Prakhya Acked-by: Vlastimil Babka I would also add something like this to reduce risk of breaking it in the future: ----8<---- diff --git a/include/linux/mm_types_task.h b/include/linux/mm_types_task.h index d7016dcb245e..a6f83cbe4603 100644 --- a/include/linux/mm_types_task.h +++ b/include/linux/mm_types_task.h @@ -36,6 +36,9 @@ struct vmacache { struct vm_area_struct *vmas[VMACACHE_SIZE]; }; +/* + * When touching this, update also resident_page_types in kernel/fork.c + */ enum { MM_FILEPAGES, /* Resident file mapping pages */ MM_ANONPAGES, /* Resident anonymous pages */