From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933973AbdKGNFs (ORCPT ); Tue, 7 Nov 2017 08:05:48 -0500 Received: from mx1.redhat.com ([209.132.183.28]:14123 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932476AbdKGNFr (ORCPT ); Tue, 7 Nov 2017 08:05:47 -0500 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com A1AEAC03BD52 Authentication-Results: ext-mx07.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx07.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=fweimer@redhat.com Subject: Re: POWER: Unexpected fault when writing to brk-allocated memory To: "Kirill A. Shutemov" Cc: Nicholas Piggin , "Aneesh Kumar K.V" , "Kirill A. Shutemov" , linuxppc-dev@lists.ozlabs.org, linux-mm , Andrew Morton , Andy Lutomirski , Dave Hansen , Linus Torvalds , Peter Zijlstra , Thomas Gleixner , linux-arch@vger.kernel.org, Ingo Molnar , Linux Kernel Mailing List References: <20171105231850.5e313e46@roar.ozlabs.ibm.com> <871slcszfl.fsf@linux.vnet.ibm.com> <20171106174707.19f6c495@roar.ozlabs.ibm.com> <24b93038-76f7-33df-d02e-facb0ce61cd2@redhat.com> <20171106192524.12ea3187@roar.ozlabs.ibm.com> <546d4155-5b7c-6dba-b642-29c103e336bc@redhat.com> <20171107160705.059e0c2b@roar.ozlabs.ibm.com> <20171107111543.ep57evfxxbwwlhdh@node.shutemov.name> <20171107114422.bgnm5k6w2zqjoazc@node.shutemov.name> From: Florian Weimer Message-ID: <7fc1641b-361c-2ee2-c510-f7c64d173bf8@redhat.com> Date: Tue, 7 Nov 2017 14:05:42 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 In-Reply-To: <20171107114422.bgnm5k6w2zqjoazc@node.shutemov.name> Content-Type: multipart/mixed; boundary="------------381B9005558AE185EB668BF2" Content-Language: en-US X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.31]); Tue, 07 Nov 2017 13:05:47 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is a multi-part message in MIME format. --------------381B9005558AE185EB668BF2 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit On 11/07/2017 12:44 PM, Kirill A. Shutemov wrote: > On Tue, Nov 07, 2017 at 12:26:12PM +0100, Florian Weimer wrote: >> On 11/07/2017 12:15 PM, Kirill A. Shutemov wrote: >> >>>> First of all, using addr and MAP_FIXED to develop our heuristic can >>>> never really give unchanged ABI. It's an in-band signal. brk() is a >>>> good example that steadily keeps incrementing address, so depending >>>> on malloc usage and address space randomization, you will get a brk() >>>> that ends exactly at 128T, then the next one will be > >>>> DEFAULT_MAP_WINDOW, and it will switch you to 56 bit address space. >>> >>> No, it won't. You will hit stack first. >> >> That's not actually true on POWER in some cases. See the process maps I >> posted here: >> >> > > Hm? I see that in all three cases the [stack] is the last mapping. > Do I miss something? Hah, I had not noticed. Occasionally, the order of heap and stack is reversed. This happens in approximately 15% of the runs. See the attached example. 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