From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756362Ab0BJSlJ (ORCPT ); Wed, 10 Feb 2010 13:41:09 -0500 Received: from www.tglx.de ([62.245.132.106]:56360 "EHLO www.tglx.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756346Ab0BJSlA (ORCPT ); Wed, 10 Feb 2010 13:41:00 -0500 Date: Wed, 10 Feb 2010 19:39:22 +0100 (CET) From: Thomas Gleixner To: Andrew Morton cc: "Serge E. Hallyn" , Tetsuo Handa , oleg@redhat.com, linux-kernel@vger.kernel.org, paulmck@linux.vnet.ibm.com, linux-security-module@vger.kernel.org Subject: Re: [PATCH] Update comment on find_task_by_pid_ns In-Reply-To: <20100210095710.c7b124f7.akpm@linux-foundation.org> Message-ID: References: <201002082130.JDC57339.OHOVJFQtFSLFMO@I-love.SAKURA.ne.jp> <20100208132101.GA7129@redhat.com> <20100208171643.GA19230@redhat.com> <201002090642.EBE48414.HLJVFOQFSOFOMt@I-love.SAKURA.ne.jp> <20100209140818.43bb9770.akpm@linux-foundation.org> <20100210163033.GA12251@us.ibm.com> <20100210095710.c7b124f7.akpm@linux-foundation.org> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 10 Feb 2010, Andrew Morton wrote: > On Wed, 10 Feb 2010 10:30:33 -0600 "Serge E. Hallyn" wrote: > > > Quoting Andrew Morton (akpm@linux-foundation.org): > > > On Tue, 9 Feb 2010 06:42:45 +0900 > > > Tetsuo Handa wrote: > > > > > > > OK. I updated description. > > > > > > > > As of 2.6.32 , below users are missing rcu_read_lock(). > > > > > > > > Users missing rcu_read_lock() when calling find_task_by_vpid(): > > > > > > > > SYSCALL_DEFINE3(ioprio_set) in fs/ioprio.c > > > > SYSCALL_DEFINE2(ioprio_get) in fs/ioprio.c > > > > cap_get_target_pid() in kernel/capability.c > > > > > > Actually, cap_get_target_pid() uses rcu_read_lock() and doesn't take > > > tasklist_lock. > > > > Hmm - is that in -mm? In my copy here it takes read_lock(&tasklist_lock) > > yup. It got changed in linux-next. > > > And I'll admit I'm a bit confused as to the current state of things: > > do I understand correctly that we now need to take both the tasklist_lock > > and rcu_read_lock? (Presumably only for read_lock()?) > > Beats me. We need to protect both the pid->task_struct lookup data > structures (during the lookup) and protect the resulting task_struct > while the caller is playing with it. It's unclear whether > rcu_read_lock() suffices for both purposes. The rcu_read_lock section is sufficient. task_struct can not go away before the rcu_read_unlock() Thanks, tglx