Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756151Ab0BJR5n (ORCPT ); Wed, 10 Feb 2010 12:57:43 -0500 Received: from smtp1.linux-foundation.org ([140.211.169.13]:60784 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754529Ab0BJR5m (ORCPT ); Wed, 10 Feb 2010 12:57:42 -0500 Date: Wed, 10 Feb 2010 09:57:10 -0800 From: Andrew Morton To: "Serge E. Hallyn" Cc: Tetsuo Handa , oleg@redhat.com, tglx@linutronix.de, 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 Message-Id: <20100210095710.c7b124f7.akpm@linux-foundation.org> In-Reply-To: <20100210163033.GA12251@us.ibm.com> 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> X-Mailer: Sylpheed 2.4.8 (GTK+ 2.12.5; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1483 Lines: 38 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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/