From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756634Ab0FYRsQ (ORCPT ); Fri, 25 Jun 2010 13:48:16 -0400 Received: from e1.ny.us.ibm.com ([32.97.182.141]:44660 "EHLO e1.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752897Ab0FYRsP (ORCPT ); Fri, 25 Jun 2010 13:48:15 -0400 Date: Fri, 25 Jun 2010 10:48:12 -0700 From: "Paul E. McKenney" To: Tetsuo Handa Cc: mingo@elte.hu, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2.6.35-rc3] Add RCU check for find_task_by_vpid(). Message-ID: <20100625174812.GF2432@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <201006260108.JFJ86910.VMFOLOFFJOtSQH@I-love.SAKURA.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201006260108.JFJ86910.VMFOLOFFJOtSQH@I-love.SAKURA.ne.jp> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jun 26, 2010 at 01:08:19AM +0900, Tetsuo Handa wrote: > find_task_by_vpid() says "Must be called under rcu_read_lock().". But due to > commit 3120438 "rcu: Disable lockdep checking in RCU list-traversal primitives", > we are currently unable to catch "find_task_by_vpid() with tasklist_lock held > but RCU lock not held" errors. > > =================================================== > [ INFO: suspicious rcu_dereference_check() usage. ] > --------------------------------------------------- > kernel/pid.c:386 invoked rcu_dereference_check() without protection! > > other info that might help us debug this: > > > rcu_scheduler_active = 1, debug_locks = 1 > 1 lock held by rc.sysinit/1102: > #0: (tasklist_lock){.+.+..}, at: [] sys_setpgid+0x40/0x160 > > stack backtrace: > Pid: 1102, comm: rc.sysinit Not tainted 2.6.35-rc3-dirty #1 > Call Trace: > [] lockdep_rcu_dereference+0x94/0xb0 > [] find_task_by_pid_ns+0x6d/0x70 > [] find_task_by_vpid+0x18/0x20 > [] sys_setpgid+0x47/0x160 > [] sysenter_do_call+0x12/0x36 > > Signed-off-by: Tetsuo Handa > --- > diff --git a/kernel/pid.c b/kernel/pid.c > index e9fd8c1..a257471 100644 > --- a/kernel/pid.c > +++ b/kernel/pid.c > @@ -382,6 +382,9 @@ EXPORT_SYMBOL(pid_task); > */ > struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns) > { > +#ifdef __do_rcu_dereference_check > + __do_rcu_dereference_check(rcu_read_lock_held()); > +#endif How about the following? WARN_ON_ONCE(!rcu_read_lock_held()); > return pid_task(find_pid_ns(nr, ns), PIDTYPE_PID); > } >