From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3yWRvb0301zDqvq for ; Tue, 7 Nov 2017 22:26:18 +1100 (AEDT) Subject: Re: POWER: Unexpected fault when writing to brk-allocated memory To: "Kirill A. Shutemov" , Nicholas Piggin Cc: "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> From: Florian Weimer Message-ID: Date: Tue, 7 Nov 2017 12:26:12 +0100 MIME-Version: 1.0 In-Reply-To: <20171107111543.ep57evfxxbwwlhdh@node.shutemov.name> Content-Type: text/plain; charset=utf-8; format=flowed List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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: Thanks, Florian