From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751330Ab1G2OcX (ORCPT ); Fri, 29 Jul 2011 10:32:23 -0400 Received: from SMTP.ANDREW.CMU.EDU ([128.2.11.95]:49724 "EHLO smtp.andrew.cmu.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750861Ab1G2OcW (ORCPT ); Fri, 29 Jul 2011 10:32:22 -0400 Date: Fri, 29 Jul 2011 10:28:43 -0400 From: Ben Blum To: NeilBrown Cc: Ben Blum , paulmck@linux.vnet.ibm.com, Paul Menage , Li Zefan , Oleg Nesterov , containers@lists.linux-foundation.org, "linux-kernel@vger.kernel.org" , Andrew Morton Subject: [PATCH][BUGFIX] cgroups: more safe tasklist locking in cgroup_attach_proc Message-ID: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110728171345.67d3797d@notabene.brown> User-Agent: Mutt/1.5.20 (2009-06-14) X-PMX-Version: 5.5.9.388399, Antispam-Engine: 2.7.2.376379, Antispam-Data: 2011.5.19.222118 X-SMTP-Spam-Clean: 8% ( BODYTEXTP_SIZE_3000_LESS 0, BODY_SIZE_1400_1499 0, BODY_SIZE_2000_LESS 0, BODY_SIZE_5000_LESS 0, BODY_SIZE_7000_LESS 0, __ANY_URI 0, __CD 0, __CT 0, __CT_TEXT_PLAIN 0, __HAS_MSGID 0, __MIME_TEXT_ONLY 0, __MIME_VERSION 0, __SANE_MSGID 0, __TO_MALFORMED_2 0, __URI_NO_PATH 0, __URI_NO_WWW 0, __USER_AGENT 0) X-SMTP-Spam-Score: 8% Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- 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.