From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754274Ab0C2Wns (ORCPT ); Mon, 29 Mar 2010 18:43:48 -0400 Received: from smtp-out.google.com ([216.239.44.51]:6445 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752527Ab0C2Wnr convert rfc822-to-8bit (ORCPT ); Mon, 29 Mar 2010 18:43:47 -0400 DomainKey-Signature: a=rsa-sha1; s=beta; d=google.com; c=nofws; q=dns; h=mime-version:in-reply-to:references:date:message-id:subject:from:to: cc:content-type:content-transfer-encoding:x-system-of-record; b=WmQFlFFNJNA/Xq7yCaoP3eGhJGNSps2P516XJ/mI43tm90JE2BjoULSu0ytHBbVNF 3iIjJ6qRueKGnBhSddLWw== MIME-Version: 1.0 In-Reply-To: <20100329211525.GA17703@linux.vnet.ibm.com> References: <20100329211525.GA17703@linux.vnet.ibm.com> Date: Mon, 29 Mar 2010 15:43:43 -0700 Message-ID: <6599ad831003291543r71300bcfv2957004bf2e927bb@mail.gmail.com> Subject: Re: [PATCH tip/core/urgent] rcu: protect fork-time cgroup access From: Paul Menage To: paulmck@linux.vnet.ibm.com 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, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, abogani@texware.it Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 29, 2010 at 2:15 PM, Paul E. McKenney wrote: > Add an rcu_read_lock() / rcu_read_unlock() pair to protect a fork-time > cgroup access.  This seems likely to be a false positive. > > Located by: Alessio Igor Bogani > Signed-off-by: Paul E. McKenney > --- > >  sched.c |    2 ++ >  1 file changed, 2 insertions(+) > > diff --git a/kernel/sched.c b/kernel/sched.c > index 9ab3cd7..d4bb5e0 100644 > --- a/kernel/sched.c > +++ b/kernel/sched.c > @@ -2621,7 +2621,9 @@ void sched_fork(struct task_struct *p, int clone_flags) >        if (p->sched_class->task_fork) >                p->sched_class->task_fork(p); > > +       rcu_read_lock(); >        set_task_cpu(p, cpu); > +       rcu_read_unlock(); I think you're right that this is a false positive - it would only be a problem if it were possible for the task to be moved to a different cgroup, and I think that shouldn't be the case at this point in the fork path since the new process isn't visible on the tasklist yet, right? Paul