From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754135Ab0C2Vvq (ORCPT ); Mon, 29 Mar 2010 17:51:46 -0400 Received: from e3.ny.us.ibm.com ([32.97.182.143]:54354 "EHLO e3.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752527Ab0C2Vvp (ORCPT ); Mon, 29 Mar 2010 17:51:45 -0400 Date: Mon, 29 Mar 2010 14:51:38 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, josh@joshtriplett.org, dvhltc@us.ibm.com, niv@us.ibm.com, tglx@linutronix.de, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, abogani@texware.it, menage@google.com, lizf@cn.fujitsu.com Subject: Re: [PATCH tip/core/urgent] rcu: protect fork-time cgroup access Message-ID: <20100329215138.GP2569@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20100329211525.GA17703@linux.vnet.ibm.com> <1269897564.12097.372.camel@laptop> <20100329212932.GO2569@linux.vnet.ibm.com> <20100329213405.GA18143@linux.vnet.ibm.com> <1269898975.12097.380.camel@laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1269898975.12097.380.camel@laptop> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 29, 2010 at 11:42:55PM +0200, Peter Zijlstra wrote: > On Mon, 2010-03-29 at 14:34 -0700, Paul E. McKenney wrote: > > > And it appears that my patch is at best insufficient: > > http://paste.ubuntu.com/406189/ > > > > Left to myself, I would wrap copy_process() with rcu_read_lock(), > > but I would rather hear your thoughts before doing too much more > > semi-random hacking. ;-) > > Well, I don't think you can get away with that, copy_process() wants to > sleep on quite a few places ;-) Also, locks should be taken at the > smallest possible scope, unless we want to go back to BKL style > locking :-) No argument here! ;-) > As to that freezer splat, you'd have to chase down the cgroup folks, I'm > fully ignorant on that. K, adding them to CC. The two splats are: http://pastebin.ubuntu.com/406131/ http://paste.ubuntu.com/406189/ Some additional RCU protection is required, or perhaps some suppression of false positives. Thoughts? > For the set_task_rq() one, I'm afraid someone (which again I'm afraid > will be me) will have to look into how the task_group muck ties into the > cgroup muck as I think the original authors of that ran off :/ Sigh! Thanx, Paul