From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752939Ab1HATca (ORCPT ); Mon, 1 Aug 2011 15:32:30 -0400 Received: from smtp-out.google.com ([74.125.121.67]:63357 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752192Ab1HATcZ convert rfc822-to-8bit (ORCPT ); Mon, 1 Aug 2011 15:32:25 -0400 DomainKey-Signature: a=rsa-sha1; s=beta; d=google.com; c=nofws; q=dns; h=dkim-signature:mime-version:in-reply-to:references:from:date: message-id:subject:to:cc:content-type: content-transfer-encoding:x-system-of-record; b=w/L/S5A1eiJubRjEPP4y0MK0cwA8F8lkyP9DzsH5G6gGD9Aze1i8T4kXW0xZ4Tm6b tDL4zyFPju9u5OfLU+p7w== MIME-Version: 1.0 In-Reply-To: <20110729142842.GA8462@unix33.andrew.cmu.edu> References: <20110727171101.5e32d8eb@notabene.brown> <20110727150710.GB5242@unix33.andrew.cmu.edu> <20110727234235.GA2318@linux.vnet.ibm.com> <20110728110813.7ff84b13@notabene.brown> <20110728062616.GC15204@unix33.andrew.cmu.edu> <20110728171345.67d3797d@notabene.brown> <20110729142842.GA8462@unix33.andrew.cmu.edu> From: Paul Menage Date: Mon, 1 Aug 2011 12:31:59 -0700 Message-ID: Subject: Re: [PATCH][BUGFIX] cgroups: more safe tasklist locking in cgroup_attach_proc To: Ben Blum Cc: NeilBrown , paulmck@linux.vnet.ibm.com, Li Zefan , Oleg Nesterov , containers@lists.linux-foundation.org, "linux-kernel@vger.kernel.org" , Andrew Morton 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 Fri, Jul 29, 2011 at 7:28 AM, Ben Blum wrote: > Fix unstable tasklist locking in cgroup_attach_proc. > > From: Ben Blum > > According to this thread - https://lkml.org/lkml/2011/7/27/243 - RCU is > not sufficient to guarantee the tasklist is stable w.r.t. de_thread and > exit. Taking tasklist_lock for reading, instead of rcu_read_lock, > ensures proper exclusion. > > Signed-off-by: Ben Blum Acked-by: Paul Menage Thanks, Paul > --- >  kernel/cgroup.c |    6 +++--- >  1 file changed, 3 insertions(+), 3 deletions(-) > > diff a/kernel/cgroup.c b/kernel/cgroup.c > --- a/kernel/cgroup.c   2011-07-21 19:17:23.000000000 -0700 > +++ b/kernel/cgroup.c   2011-07-29 06:17:47.000000000 -0700 > @@ -2024,7 +2024,7 @@ >                goto out_free_group_list; > >        /* prevent changes to the threadgroup list while we take a snapshot. */ > -       rcu_read_lock(); > +       read_lock(&tasklist_lock); >        if (!thread_group_leader(leader)) { >                /* >                 * a race with de_thread from another thread's exec() may strip > @@ -2033,7 +2033,7 @@ >                 * throw this task away and try again (from cgroup_procs_write); >                 * this is "double-double-toil-and-trouble-check locking". >                 */ > -               rcu_read_unlock(); > +               read_unlock(&tasklist_lock); >                retval = -EAGAIN; >                goto out_free_group_list; >        } > @@ -2054,7 +2054,7 @@ >        } while_each_thread(leader, tsk); >        /* remember the number of threads in the array for later. */ >        group_size = i; > -       rcu_read_unlock(); > +       read_unlock(&tasklist_lock); > >        /* >         * step 1: check that we can legitimately attach to the cgroup. >