Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753214AbdDKGfG (ORCPT ); Tue, 11 Apr 2017 02:35:06 -0400 Received: from mx2.suse.de ([195.135.220.15]:37639 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752488AbdDKGfE (ORCPT ); Tue, 11 Apr 2017 02:35:04 -0400 Subject: Re: [PATCH] mm, numa: Fix bad pmd by atomically check for pmd_trans_huge when marking page tables prot_numa To: Zi Yan , Andrew Morton References: <20170410094825.2yfo5zehn7pchg6a@techsingularity.net> <84B5E286-4E2A-4DE0-8351-806D2102C399@cs.rutgers.edu> <20170410172056.shyx6qzcjglbt5nd@techsingularity.net> <8A6309F4-DB76-48FA-BE7F-BF9536A4C4E5@cs.rutgers.edu> <20170410180714.7yfnxl7qin72jcob@techsingularity.net> <20170410150903.f931ceb5475d2d3d8945bb71@linux-foundation.org> <789A2322-A5B6-4AC8-8668-D7057A56A140@cs.rutgers.edu> Cc: Mel Gorman , "Kirill A. Shutemov" , Andrea Arcangeli , Rik van Riel , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org From: Vlastimil Babka Message-ID: <6336c469-c946-c300-7392-87052c990266@suse.cz> Date: Tue, 11 Apr 2017 08:35:02 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <789A2322-A5B6-4AC8-8668-D7057A56A140@cs.rutgers.edu> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3228 Lines: 78 On 04/11/2017 12:28 AM, Zi Yan wrote: > On 10 Apr 2017, at 17:09, Andrew Morton wrote: > >> On Mon, 10 Apr 2017 19:07:14 +0100 Mel Gorman wrote: >> >>> On Mon, Apr 10, 2017 at 12:49:40PM -0500, Zi Yan wrote: >>>> On 10 Apr 2017, at 12:20, Mel Gorman wrote: >>>> >>>>> On Mon, Apr 10, 2017 at 11:45:08AM -0500, Zi Yan wrote: >>>>>>> While this could be fixed with heavy locking, it's only necessary to >>>>>>> make a copy of the PMD on the stack during change_pmd_range and avoid >>>>>>> races. A new helper is created for this as the check if quite subtle and the >>>>>>> existing similar helpful is not suitable. This passed 154 hours of testing >>>>>>> (usually triggers between 20 minutes and 24 hours) without detecting bad >>>>>>> PMDs or corruption. A basic test of an autonuma-intensive workload showed >>>>>>> no significant change in behaviour. >>>>>>> >>>>>>> Signed-off-by: Mel Gorman >>>>>>> Cc: stable@vger.kernel.org >>>>>> >>>>>> Does this patch fix the same problem fixed by Kirill's patch here? >>>>>> https://lkml.org/lkml/2017/3/2/347 >>>>>> >>>>> >>>>> I don't think so. The race I'm concerned with is due to locks not being >>>>> held and is in a different path. >>>> >>>> I do not agree. Kirill's patch is fixing the same race problem but in >>>> zap_pmd_range(). >>>> >>>> The original autoNUMA code first clears PMD then sets it to protnone entry. >>>> pmd_trans_huge() does not return TRUE because it saw cleared PMD, but >>>> pmd_none_or_clear_bad() later saw the protnone entry and reported it as bad. >>>> Is this the problem you are trying solve? >>>> >>>> Kirill's patch will pmdp_invalidate() the PMD entry, which keeps _PAGE_PSE bit, >>>> so pmd_trans_huge() will return TRUE. In this case, it also fixes >>>> your race problem in change_pmd_range(). >>>> >>>> Let me know if I miss anything. >>>> >>> >>> Ok, now I see. I think you're correct and I withdraw the patch. >> >> I have Kirrill's >> >> thp-reduce-indentation-level-in-change_huge_pmd.patch >> thp-fix-madv_dontneed-vs-numa-balancing-race.patch >> mm-drop-unused-pmdp_huge_get_and_clear_notify.patch >> thp-fix-madv_dontneed-vs-madv_free-race.patch >> thp-fix-madv_dontneed-vs-madv_free-race-fix.patch >> thp-fix-madv_dontneed-vs-clear-soft-dirty-race.patch >> >> scheduled for 4.12-rc1. It sounds like >> thp-fix-madv_dontneed-vs-madv_free-race.patch and >> thp-fix-madv_dontneed-vs-madv_free-race.patch need to be boosted to >> 4.11 and stable? > > thp-fix-madv_dontneed-vs-numa-balancing-race.patch is the fix for > numa balancing problem reported in this thread. > > mm-drop-unused-pmdp_huge_get_and_clear_notify.patch, > thp-fix-madv_dontneed-vs-madv_free-race.patch, > thp-fix-madv_dontneed-vs-madv_free-race-fix.patch, and > thp-fix-madv_dontneed-vs-clear-soft-dirty-race.patch > > are the fixes for other potential race problems similar to this one. > > I think it is better to have all these patches applied. Yeah we should get all such fixes to stable IMHO (after review :). It's not the first time that a fix for MADV_DONTNEED turned out to also fix a race that involved "normal operation" with THP, without such syscalls. > -- > Best Regards > Yan Zi >