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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, 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 5804EC0044C for ; Wed, 31 Oct 2018 06:32:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 11B6520821 for ; Wed, 31 Oct 2018 06:32:00 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 11B6520821 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 S1729177AbeJaP2o (ORCPT ); Wed, 31 Oct 2018 11:28:44 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:43108 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726287AbeJaP2n (ORCPT ); Wed, 31 Oct 2018 11:28:43 -0400 Received: from pps.filterd (m0098420.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w9V6KHjI037779 for ; Wed, 31 Oct 2018 02:31:57 -0400 Received: from e06smtp02.uk.ibm.com (e06smtp02.uk.ibm.com [195.75.94.98]) by mx0b-001b2d01.pphosted.com with ESMTP id 2nf3paxwma-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Wed, 31 Oct 2018 02:31:57 -0400 Received: from localhost by e06smtp02.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) Wed, 31 Oct 2018 06:31:52 -0000 Received: from d06av21.portsmouth.uk.ibm.com (d06av21.portsmouth.uk.ibm.com [9.149.105.232]) by b06cxnps4074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id w9V6Vpv965142844 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Wed, 31 Oct 2018 06:31:51 GMT Received: from d06av21.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 6342952063; Wed, 31 Oct 2018 06:31:51 +0000 (GMT) Received: from mschwideX1 (unknown [9.145.41.78]) by d06av21.portsmouth.uk.ibm.com (Postfix) with ESMTP id 02A6D52052; Wed, 31 Oct 2018 06:31:50 +0000 (GMT) Date: Wed, 31 Oct 2018 07:31:49 +0100 From: Martin Schwidefsky To: Li Wang Cc: Guenter Roeck , Janosch Frank , "Kirill A. Shutemov" , Heiko Carstens , linux-kernel , Linux-MM Subject: Re: [PATCH 3/3] s390/mm: fix mis-accounting of pgtable_bytes In-Reply-To: References: <1539621759-5967-1-git-send-email-schwidefsky@de.ibm.com> <1539621759-5967-4-git-send-email-schwidefsky@de.ibm.com> X-Mailer: Claws Mail 3.13.2 (GTK+ 2.24.30; x86_64-pc-linux-gnu) MIME-Version: 1.0 X-TM-AS-GCONF: 00 x-cbid: 18103106-0008-0000-0000-00000288D04B X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18103106-0009-0000-0000-000021F2EFD8 Message-Id: <20181031073149.55ddc085@mschwideX1> Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8bit X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-10-31_02:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 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=8.0.1-1807170000 definitions=main-1810310054 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 31 Oct 2018 14:18:33 +0800 Li Wang wrote: > On Tue, Oct 16, 2018 at 12:42 AM, Martin Schwidefsky > wrote: > > > In case a fork or a clone system fails in copy_process and the error > > handling does the mmput() at the bad_fork_cleanup_mm label, the > > following warning messages will appear on the console: > > > > BUG: non-zero pgtables_bytes on freeing mm: 16384 > > > > The reason for that is the tricks we play with mm_inc_nr_puds() and > > mm_inc_nr_pmds() in init_new_context(). > > > > A normal 64-bit process has 3 levels of page table, the p4d level and > > the pud level are folded. On process termination the free_pud_range() > > function in mm/memory.c will subtract 16KB from pgtable_bytes with a > > mm_dec_nr_puds() call, but there actually is not really a pud table. > > > > One issue with this is the fact that pgtable_bytes is usually off > > by a few kilobytes, but the more severe problem is that for a failed > > fork or clone the free_pgtables() function is not called. In this case > > there is no mm_dec_nr_puds() or mm_dec_nr_pmds() that go together with > > the mm_inc_nr_puds() and mm_inc_nr_pmds in init_new_context(). > > The pgtable_bytes will be off by 16384 or 32768 bytes and we get the > > BUG message. The message itself is purely cosmetic, but annoying. > > > > To fix this override the mm_pmd_folded, mm_pud_folded and mm_p4d_folded > > function to check for the true size of the address space. > > > > I can confirm that it works to the problem, the warning message is gone > after applying this patch on s390x. And I also done ltp syscalls/cve test > for the patch set on x86_64 arch, there has no new regression. > > Tested-by: Li Wang 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. -- blue skies, Martin. "Reality continues to ruin my life." - Calvin.