From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f69.google.com (mail-ed1-f69.google.com [209.85.208.69]) by kanga.kvack.org (Postfix) with ESMTP id 8CC788E0001 for ; Thu, 27 Sep 2018 09:21:13 -0400 (EDT) Received: by mail-ed1-f69.google.com with SMTP id j1-v6so3015867edq.23 for ; Thu, 27 Sep 2018 06:21:13 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id h16-v6si284463ejp.119.2018.09.27.06.21.12 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 27 Sep 2018 06:21:12 -0700 (PDT) Subject: Re: [v2 PATCH 2/2 -mm] mm: brk: dwongrade mmap_sem to read when shrinking References: <1537985434-22655-1-git-send-email-yang.shi@linux.alibaba.com> <1537985434-22655-2-git-send-email-yang.shi@linux.alibaba.com> <20180927125025.xnvoh2btdq5kjmai@kshutemo-mobl1> From: Vlastimil Babka Message-ID: <3ba966a4-abf9-1363-3e82-41fe73bc0919@suse.cz> Date: Thu, 27 Sep 2018 15:21:09 +0200 MIME-Version: 1.0 In-Reply-To: <20180927125025.xnvoh2btdq5kjmai@kshutemo-mobl1> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: "Kirill A. Shutemov" , Yang Shi Cc: mhocko@kernel.org, willy@infradead.org, ldufour@linux.vnet.ibm.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On 9/27/18 2:50 PM, Kirill A. Shutemov wrote: >> diff --git a/mm/mmap.c b/mm/mmap.c >> index 017bcfa..0d2fae1 100644 >> --- a/mm/mmap.c >> +++ b/mm/mmap.c >> @@ -193,9 +193,11 @@ static int do_brk_flags(unsigned long addr, unsigned long request, unsigned long >> unsigned long retval; >> unsigned long newbrk, oldbrk; >> struct mm_struct *mm = current->mm; >> + unsigned long origbrk = mm->brk; > > Is it safe to read mm->brk outside the lock? Good catch! I guess not, parallel brk()'s could then race.