From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl0-f72.google.com (mail-pl0-f72.google.com [209.85.160.72]) by kanga.kvack.org (Postfix) with ESMTP id 83D116B0003 for ; Tue, 10 Apr 2018 07:10:08 -0400 (EDT) Received: by mail-pl0-f72.google.com with SMTP id f9-v6so9270648plo.17 for ; Tue, 10 Apr 2018 04:10:08 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id f9-v6si2475320pln.45.2018.04.10.04.10.07 for (version=TLS1 cipher=AES128-SHA bits=128/128); Tue, 10 Apr 2018 04:10:07 -0700 (PDT) Date: Tue, 10 Apr 2018 13:10:01 +0200 From: Michal Hocko Subject: Re: [v3 PATCH] mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct Message-ID: <20180410111001.GD21835@dhcp22.suse.cz> References: <1523310774-40300-1-git-send-email-yang.shi@linux.alibaba.com> <20180410090917.GZ21835@dhcp22.suse.cz> <20180410094047.GB2041@uranus.lan> <20180410104215.GB21835@dhcp22.suse.cz> <20180410110242.GC2041@uranus.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180410110242.GC2041@uranus.lan> Sender: owner-linux-mm@kvack.org List-ID: To: Cyrill Gorcunov Cc: Yang Shi , adobriyan@gmail.com, willy@infradead.org, mguzik@redhat.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On Tue 10-04-18 14:02:42, Cyrill Gorcunov wrote: > On Tue, Apr 10, 2018 at 12:42:15PM +0200, Michal Hocko wrote: > > On Tue 10-04-18 12:40:47, Cyrill Gorcunov wrote: > > > On Tue, Apr 10, 2018 at 11:09:17AM +0200, Michal Hocko wrote: > > > > On Tue 10-04-18 05:52:54, Yang Shi wrote: > > > > [...] > > > > > So, introduce a new spinlock in mm_struct to protect the concurrent > > > > > access to arg_start|end, env_start|end and others except start_brk and > > > > > brk, which are still protected by mmap_sem to avoid concurrent access > > > > > from do_brk(). > > > > > > > > Is there any fundamental problem with brk using the same lock? > > > > > > Seems so. Look into mm/mmap.c:brk syscall which reads and writes > > > brk value under mmap_sem ('cause of do_brk called inside). > > > > Why cannot we simply use the lock when the value is updated? > > Because do_brk does vma manipulations, for this reason it's > running under down_write_killable(&mm->mmap_sem). Or you > mean something else? Yes, all we need the new lock for is to get a consistent view on brk values. I am simply asking whether there is something fundamentally wrong by doing the update inside the new lock while keeping the original mmap_sem locking in the brk path. That would allow us to drop the mmap_sem lock in the proc path when looking at brk values. -- Michal Hocko SUSE Labs