From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753965Ab1JLSdb (ORCPT ); Wed, 12 Oct 2011 14:33:31 -0400 Received: from mx1.redhat.com ([209.132.183.28]:10936 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752002Ab1JLSda (ORCPT ); Wed, 12 Oct 2011 14:33:30 -0400 Date: Wed, 12 Oct 2011 20:29:05 +0200 From: Oleg Nesterov To: Ben Blum Cc: Tejun Heo , rjw@sisk.pl, paul@paulmenage.org, lizf@cn.fujitsu.com, linux-pm@lists.linux-foundation.org, linux-kernel@vger.kernel.org, containers@lists.linux-foundation.org, fweisbec@gmail.com, matthltc@us.ibm.com, akpm@linux-foundation.org, Paul Menage Subject: Re: [PATCH 3/4] threadgroup: extend threadgroup_lock() to cover exit and exec Message-ID: <20111012182905.GA8580@redhat.com> References: <1315159280-25032-1-git-send-email-htejun@gmail.com> <1315159280-25032-4-git-send-email-htejun@gmail.com> <20110918173723.GA2384@redhat.com> <20111010171105.GE8100@google.com> <20111012175104.GA6156@redhat.com> <20111012180521.GA20715@ghc17.ghc.andrew.cmu.edu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20111012180521.GA20715@ghc17.ghc.andrew.cmu.edu> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/12, Ben Blum wrote: > > On Wed, Oct 12, 2011 at 07:51:04PM +0200, Oleg Nesterov wrote: > > > > > Also, it makes the mechanism unnecessarily cgroup-specific without > > > gaining much if anything. > > > > Yes! And _personally_ I think it should be cgroup-specific, that is > > why I dislike the very fact do_exit() uses it directly. To me it would > > be cleaner to shift it into cgroup hooks. Yes, sure, this is subjective. > > In the fork path, threadgroup_fork_read_...() is also called directly, > not through cgroups. Would that change too? Well, if you ask me, I'd prefer to move lock/unlock into cgroup_fork/cgroup_post_fork ;) Although the error path plays with it too. But this is minor. > > In fact I still hope we can kill this sem altogether, but so far I have > > no idea how we can do this. We do need the new per-process lock to > > protect (in particular) ->thread_group. It is quite possible that it > > should be rw_semaphore. But in this case we down_write(), not _read > > in exit/fork paths, and its scope should be small. > > I'm confused - taking a big rwsem for writing in the fork/exit paths? Yes, we need the new lock to avoid tasklist_lock. > The point here is that even though fork/exit modify thread_group, they > are logical "readers" Yes I see. And this is one of the reasons why we can't use this lock for above. Oleg.