From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753226AbdFVK6z (ORCPT ); Thu, 22 Jun 2017 06:58:55 -0400 Received: from mail-eopbgr50109.outbound.protection.outlook.com ([40.107.5.109]:47419 "EHLO EUR03-VE1-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752972AbdFVK6w (ORCPT ); Thu, 22 Jun 2017 06:58:52 -0400 Authentication-Results: virtuozzo.com; dkim=none (message not signed) header.d=none;virtuozzo.com; dmarc=none action=none header.from=virtuozzo.com; Subject: Re: [lkp-robot] [mm] 1be7107fbe: kernel_BUG_at_mm/mmap.c To: Hugh Dickins , Oleg Nesterov Cc: Linus Torvalds , Cyrill Gorcunov , Andrey Vagin , Pavel Emelyanov , Andrew Morton , Adrian Reber , Michael Kerrisk , Willy Tarreau , kernel test robot , Michal Hocko , LKML , LKP References: <20170621023552.GB32082@yexl-desktop> <20170621193338.GA29222@redhat.com> <20170621202751.GA29638@redhat.com> <20170621205617.GA29841@redhat.com> From: Dmitry Safonov Message-ID: <96e0b5fc-e71e-46d4-a246-5ff9ec65383d@virtuozzo.com> Date: Thu, 22 Jun 2017 13:58:42 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [195.214.232.6] X-ClientProxiedBy: AM5PR0502CA0016.eurprd05.prod.outlook.com (2603:10a6:203:91::26) To DB6PR0801MB1733.eurprd08.prod.outlook.com (2603:10a6:4:3a::20) X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 988dbf59-85f7-4b45-73c5-08d4b95da85d X-Microsoft-Antispam: UriScan:;BCL:0;PCL:0;RULEID:(22001)(201703131423075)(201703031133081);SRVR:DB6PR0801MB1733; X-Microsoft-Exchange-Diagnostics: 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1;DB6PR0801MB1733;7: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 X-Microsoft-Exchange-Diagnostics: 1;DB6PR0801MB1733;20:J5IAJCdMqd/qfYUNIiMjAn6L5bWy6urdfWQc52YW6NEyiYZqbO0rzKGFkLJPvrwfbO99DObgHqsD17EXLmvyjQeaegb/bpQEpNgsuzNNkDM5pPkwDsQ8AK89R6UVFP74GTwj9HO2bqP3Rmo9NGmf3/WM+53nnrS0MDBfMYSJV3c= X-OriginatorOrg: virtuozzo.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 22 Jun 2017 10:58:46.2470 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-Transport-CrossTenantHeadersStamped: DB6PR0801MB1733 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/22/2017 04:07 AM, Hugh Dickins wrote: > On Wed, 21 Jun 2017, Linus Torvalds wrote: >> On Wed, Jun 21, 2017 at 1:56 PM, Oleg Nesterov wrote: >>> >>> I understand. My point is that this check was invalidated by stack-guard-page >>> a long ago, and this means that we add the user-visible change now. >> >> Yeah. I guess we could consider it an *old* regression that got fixed, >> but if people started relying on the regression... >> >>>> Do you have a pointer to the report for this regression? I must have missed it. >>> >>> See http://marc.info/?t=149794523000001&r=1&w=2 >> >> Ok. >> >> And thinking about it, while that is a silly test-case, the notion of >> "create top-down segment, then start populating it _before_ moving the >> stack pointer into it" is actually perfectly valid. >> >> So I guess checking against the stack pointer is wrong in that case - >> at least if the stack pointer isn't inside that vma to begin with. >> >> So yes, removing that check looks like the right thing to do for now. >> >> Do you want to send me the patch if you already have a commit message etc? > > I have a bit of a bad feeling about this. > > Perhaps it's just sentimental attachment to all those weird > and ancient stack pointer checks in arch//fault.c. > > We have been inconsistent: cris frv m32r m68k microblaze mn10300 > openrisc powerpc tile um x86 have such checks, the others don't. > So that's a good reason to delete them. > > But at least at the moment those checks impose some sanity: > just a page less than we had imagined for several years. > Once we remove them, they cannot go back. Should we now > complicate them with an extra page of slop? > > I'm not entirely persuaded by your pre-population argument: > it's perfectly possible to prepare a MAP_GROWSDOWN area with > an initial size, that's populated in a normal way, before handing > off for stack expansion - isn't it? > > I'd be interested to hear more about that (redhat internal) bug > report that Oleg mentions: whether it gives stronger grounds for > making this sudden change than the CRIU testcase. Well, if all the deal is in CRIU testcase - it can be easily reworked. The question - will it break anything else? Maybe it's better to disable this check on the release and enable it back for v4.13 kernel, so if it'll break some user-space, it'll be caught on linux-next. > > I can go ahead and create a patch if Oleg is not there at the > moment - but I might prefer his or your name on it - particularly > if we're rushing it in before consulting the arch maintainers > whose work we would be deleting. > > Queasily, > Hugh > -- Dmitry From mboxrd@z Thu Jan 1 00:00:00 1970 Content-Type: multipart/mixed; boundary="===============5765917488604031741==" MIME-Version: 1.0 From: Dmitry Safonov To: lkp@lists.01.org Subject: Re: [lkp-robot] [mm] 1be7107fbe: kernel_BUG_at_mm/mmap.c Date: Thu, 22 Jun 2017 13:58:42 +0300 Message-ID: <96e0b5fc-e71e-46d4-a246-5ff9ec65383d@virtuozzo.com> In-Reply-To: List-Id: --===============5765917488604031741== Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable On 06/22/2017 04:07 AM, Hugh Dickins wrote: > On Wed, 21 Jun 2017, Linus Torvalds wrote: >> On Wed, Jun 21, 2017 at 1:56 PM, Oleg Nesterov wrote: >>> >>> I understand. My point is that this check was invalidated by stack-guar= d-page >>> a long ago, and this means that we add the user-visible change now. >> >> Yeah. I guess we could consider it an *old* regression that got fixed, >> but if people started relying on the regression... >> >>>> Do you have a pointer to the report for this regression? I must have m= issed it. >>> >>> See http://marc.info/?t=3D149794523000001&r=3D1&w=3D2 >> >> Ok. >> >> And thinking about it, while that is a silly test-case, the notion of >> "create top-down segment, then start populating it _before_ moving the >> stack pointer into it" is actually perfectly valid. >> >> So I guess checking against the stack pointer is wrong in that case - >> at least if the stack pointer isn't inside that vma to begin with. >> >> So yes, removing that check looks like the right thing to do for now. >> >> Do you want to send me the patch if you already have a commit message et= c? > = > I have a bit of a bad feeling about this. > = > Perhaps it's just sentimental attachment to all those weird > and ancient stack pointer checks in arch//fault.c. > = > We have been inconsistent: cris frv m32r m68k microblaze mn10300 > openrisc powerpc tile um x86 have such checks, the others don't. > So that's a good reason to delete them. > = > But at least at the moment those checks impose some sanity: > just a page less than we had imagined for several years. > Once we remove them, they cannot go back. Should we now > complicate them with an extra page of slop? > = > I'm not entirely persuaded by your pre-population argument: > it's perfectly possible to prepare a MAP_GROWSDOWN area with > an initial size, that's populated in a normal way, before handing > off for stack expansion - isn't it? > = > I'd be interested to hear more about that (redhat internal) bug > report that Oleg mentions: whether it gives stronger grounds for > making this sudden change than the CRIU testcase. Well, if all the deal is in CRIU testcase - it can be easily reworked. The question - will it break anything else? Maybe it's better to disable this check on the release and enable it back for v4.13 kernel, so if it'll break some user-space, it'll be caught on linux-next. > = > I can go ahead and create a patch if Oleg is not there at the > moment - but I might prefer his or your name on it - particularly > if we're rushing it in before consulting the arch maintainers > whose work we would be deleting. > = > Queasily, > Hugh > = -- = Dmitry --===============5765917488604031741==--