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=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 BC72DC31E40 for ; Tue, 6 Aug 2019 08:36:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8FF6720B1F for ; Tue, 6 Aug 2019 08:36:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1565080570; bh=svvM3Fbdv5OJ+mOWPULJjtihgyToVM10EGE8QHliNKE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=u00h0nulss+Z7PrVH70gqYWAKPvUvrE/f5/MEd+3/G+2gXxXsygM8VubWhl/ZeawP gyP1PRudxFkJ8QlnJDOZ2TClnxZWa/n61bh3SnOwfAnfYIdWISAPRUXToJUoqgYdcA 0H7bCRyPP5JuZ+Ef67VABIOIj3RV/laLugiN4cWc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732289AbfHFIgJ (ORCPT ); Tue, 6 Aug 2019 04:36:09 -0400 Received: from mx2.suse.de ([195.135.220.15]:57730 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728845AbfHFIgJ (ORCPT ); Tue, 6 Aug 2019 04:36:09 -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 3ACB5ABC7; Tue, 6 Aug 2019 08:36:07 +0000 (UTC) Date: Tue, 6 Aug 2019 10:36:05 +0200 From: Michal Hocko To: Sai Praneeth Prakhya Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, dave.hansen@intel.com, Ingo Molnar , Vlastimil Babka , Peter Zijlstra , Andrew Morton , Anshuman Khandual Subject: Re: [PATCH V2] fork: Improve error message for corrupted page tables Message-ID: <20190806083605.GA19060@dhcp22.suse.cz> References: <3ef8a340deb1c87b725d44edb163073e2b6eca5a.1565059496.git.sai.praneeth.prakhya@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3ef8a340deb1c87b725d44edb163073e2b6eca5a.1565059496.git.sai.praneeth.prakhya@intel.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 05-08-19 20:05:27, 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 I like this. On any occasion I am investigating an issue with an rss inbalance I have to go back to kernel sources to see which pte type that is. > Also, change print function (from printk(KERN_ALERT, ..) to pr_alert()) so > that it matches the other print statement. good change as well. Maybe we should also lower the loglevel (in a separate patch) as well. While this is not nice because we are apparently leaking memory behind it shouldn't be really critical enough to jump on normal consoles. > 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: Michal Hocko > --- > > Changes from V1 to V2: > ---------------------- > 1. Move struct definition from header file to fork.c file, so that it won't be > included in every compilation unit. As this struct is used *only* in fork.c, > include the definition in fork.c itself. > 2. Index the struct to match respective macros. > 3. Mention about print function change in commit message. > > kernel/fork.c | 11 +++++++++-- > 1 file changed, 9 insertions(+), 2 deletions(-) > > diff --git a/kernel/fork.c b/kernel/fork.c > index d8ae0f1b4148..f34f441c50c0 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -125,6 +125,13 @@ int nr_threads; /* The idle threads do not count.. */ > > static int max_threads; /* tunable limit on nr_threads */ > > +static const char * const resident_page_types[NR_MM_COUNTERS] = { > + [MM_FILEPAGES] = "MM_FILEPAGES", > + [MM_ANONPAGES] = "MM_ANONPAGES", > + [MM_SWAPENTS] = "MM_SWAPENTS", > + [MM_SHMEMPAGES] = "MM_SHMEMPAGES", > +}; > + > DEFINE_PER_CPU(unsigned long, process_counts) = 0; > > __cacheline_aligned DEFINE_RWLOCK(tasklist_lock); /* outer */ > @@ -649,8 +656,8 @@ static void check_mm(struct mm_struct *mm) > long x = atomic_long_read(&mm->rss_stat.count[i]); > > if (unlikely(x)) > - printk(KERN_ALERT "BUG: Bad rss-counter state " > - "mm:%p idx:%d val:%ld\n", mm, i, x); > + pr_alert("BUG: Bad rss-counter state mm:%p type:%s val:%ld\n", > + mm, resident_page_types[i], x); > } > > if (mm_pgtables_bytes(mm)) > -- > 2.7.4 -- Michal Hocko SUSE Labs