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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS 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 21FABC43441 for ; Tue, 27 Nov 2018 07:34:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E524220989 for ; Tue, 27 Nov 2018 07:34:27 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E524220989 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=de.ibm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729142AbeK0SbY (ORCPT ); Tue, 27 Nov 2018 13:31:24 -0500 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:42736 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727631AbeK0SbX (ORCPT ); Tue, 27 Nov 2018 13:31:23 -0500 Received: from pps.filterd (m0098421.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id wAR7YPEE023376 for ; Tue, 27 Nov 2018 02:34:25 -0500 Received: from e06smtp03.uk.ibm.com (e06smtp03.uk.ibm.com [195.75.94.99]) by mx0a-001b2d01.pphosted.com with ESMTP id 2p117r10f6-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Tue, 27 Nov 2018 02:34:24 -0500 Received: from localhost by e06smtp03.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Tue, 27 Nov 2018 07:34:14 -0000 Received: from d06av24.portsmouth.uk.ibm.com (d06av24.portsmouth.uk.ibm.com [9.149.105.60]) by b06cxnps4074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id wAR7YDoo4129234 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Tue, 27 Nov 2018 07:34:13 GMT Received: from d06av24.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id A840C42047; Tue, 27 Nov 2018 07:34:13 +0000 (GMT) Received: from d06av24.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 66D7E42041; Tue, 27 Nov 2018 07:34:13 +0000 (GMT) Received: from osiris (unknown [9.152.212.95]) by d06av24.portsmouth.uk.ibm.com (Postfix) with ESMTPS; Tue, 27 Nov 2018 07:34:13 +0000 (GMT) Date: Tue, 27 Nov 2018 08:34:12 +0100 From: Heiko Carstens To: "Kirill A. Shutemov" Cc: "Kirill A. Shutemov" , Li Wang , Guenter Roeck , Janosch Frank , linux-kernel , Linux-MM , Martin Schwidefsky Subject: Re: [PATCH 3/3] s390/mm: fix mis-accounting of pgtable_bytes References: <1539621759-5967-1-git-send-email-schwidefsky@de.ibm.com> <1539621759-5967-4-git-send-email-schwidefsky@de.ibm.com> <20181031073149.55ddc085@mschwideX1> <20181031100944.GA3546@osiris> <20181031103623.6ykzsjdenrpeth7x@kshutemo-mobl1> MIME-Version: 1.0 In-Reply-To: <20181031103623.6ykzsjdenrpeth7x@kshutemo-mobl1> X-TM-AS-GCONF: 00 x-cbid: 18112707-0012-0000-0000-000002D0BD86 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18112707-0013-0000-0000-00002105FD36 Message-Id: <20181127073411.GA3625@osiris> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 8bit Content-Disposition: inline X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-11-27_07:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=1 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1811270069 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 31, 2018 at 01:36:23PM +0300, Kirill A. Shutemov wrote: > On Wed, Oct 31, 2018 at 11:09:44AM +0100, Heiko Carstens wrote: > > On Wed, Oct 31, 2018 at 07:31:49AM +0100, Martin Schwidefsky wrote: > > > Thanks for testing. Unfortunately Heiko reported another issue yesterday > > > with the patch applied. This time the other way around: > > > > > > BUG: non-zero pgtables_bytes on freeing mm: -16384 > > > > > > I am trying to understand how this can happen. For now I would like to > > > keep the patch on hold in case they need another change. > > > > FWIW, Kirill: is there a reason why this "BUG:" output is done with > > pr_alert() and not with VM_BUG_ON() or one of the WARN*() variants? > > > > That would to get more information with DEBUG_VM and / or > > panic_on_warn=1 set. At least for automated testing it would be nice > > to have such triggers. > > Stack trace is not helpful there. It will always show the exit path which > is useless. So, even with the updated version of these patches I can flood dmesg and the console with BUG: non-zero pgtables_bytes on freeing mm: 16384 messages with this complex reproducer on s390: echo "void main(void) {}" | gcc -m31 -xc -o compat - && ./compat Besides that this needs to be fixed, I'd really like to see this changed to either a printk_once() or a WARN_ON_ONCE() within check_mm() so that an arbitrary user cannot flood the console. E.g. something like the below. If there aren't any objections, I will provide a proper patch with changelog, etc. diff --git a/kernel/fork.c b/kernel/fork.c index 07cddff89c7b..d7aeec03c57f 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -647,8 +647,8 @@ static void check_mm(struct mm_struct *mm) } if (mm_pgtables_bytes(mm)) - pr_alert("BUG: non-zero pgtables_bytes on freeing mm: %ld\n", - mm_pgtables_bytes(mm)); + printk_once(KERN_ALERT "BUG: non-zero pgtables_bytes on freeing mm: %ld\n", + mm_pgtables_bytes(mm)); #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS VM_BUG_ON_MM(mm->pmd_huge_pte, mm);