Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932123Ab0HPUV3 (ORCPT ); Mon, 16 Aug 2010 16:21:29 -0400 Received: from e5.ny.us.ibm.com ([32.97.182.145]:42572 "EHLO e5.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756410Ab0HPUV1 (ORCPT ); Mon, 16 Aug 2010 16:21:27 -0400 Date: Mon, 16 Aug 2010 13:21:24 -0700 From: "Paul E. McKenney" To: Vegard Nossum Cc: Nick Piggin , Peter Zijlstra , David Howells , LKML Subject: Re: 2.6.35+vfs-scale: INFO: suspicious rcu_dereference_check() usage (kernel/exit.c:1387) Message-ID: <20100816202124.GI2388@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References:

MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: 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 Content-Length: 3711 Lines: 102 On Mon, Aug 16, 2010 at 07:03:40PM +0200, Vegard Nossum wrote: > On the third try it will hopefully work. > > > Vegard > > ---------- Forwarded message ---------- > From: Vegard Nossum > Date: 16 August 2010 19:01 > Subject: Re: 2.6.35+vfs-scale: INFO: suspicious > rcu_dereference_check() usage (kernel/exit.c:1387) > To: Nick Piggin > Cc: Peter Zijlstra , David Howells > , "Paul E. McKenney" > , LKML > > > Nick Piggin might update his git config because the commits in the > vfs-scale tree appear to bear an invalid e-mail address. Please reply > to this e-mail instead. Thanks. > > Vegard > > > ---------- Forwarded message ---------- > From: Vegard Nossum > Date: 16 August 2010 18:57 > Subject: 2.6.35+vfs-scale: INFO: suspicious rcu_dereference_check() > usage (kernel/exit.c:1387) > To: Nick Piggin > Cc: Peter Zijlstra , David Howells > , "Paul E. McKenney" > , LKML > > > Hi, > > I was testing your VFS scaling tree*, but I get the following in my dmesg: > > =================================================== > [ INFO: suspicious rcu_dereference_check() usage. ] > --------------------------------------------------- > kernel/exit.c:1387 invoked rcu_dereference_check() without protection! > > other info that might help us debug this: > > > rcu_scheduler_active = 1, debug_locks = 1 > 2 locks held by bash/2878: > ?#0: ?(tasklist_lock){.+.+..}, at: [] do_wait+0xb3/0x200 > ?#1: ?(&(&sighand->siglock)->rlock){-.....}, at: [] > wait_consider_task+0x2ca/0xaa3 Thank you for locating this! OK, so we aren't holding rcu_read_lock(), nor is this task dead, so something needs some help. We get from wait_consider_task() as follows: wait_consider_task() calls security_task_wait(), which calls either selinux_task_wait() or smack_task_wait(). Let's start with selinux_task_wait(), which calls task_has_perm(), which does a couple of __task_cred(), but does so under rcu_read_lock() protection, so presumably we didn't come in that way. Dave, am I missing a code path somewhere here? Thanx, Paul > stack backtrace: > Pid: 2878, comm: bash Not tainted 2.6.35-00079-g4067b85 #7 > Call Trace: > ?[] lockdep_rcu_dereference+0x9b/0xa6 > ?[] wait_consider_task+0x917/0xaa3 > ?[] ? add_preempt_count+0xc2/0xc9 > ?[] do_wait+0xdb/0x200 > ?[] sys_wait4+0x99/0xd3 > ?[] ? child_wait_callback+0x0/0x5d > ?[] ? might_fault+0x96/0xbc > ?[] compat_sys_wait4+0x8a/0xc1 > ?[] ? might_fault+0xb3/0xbc > ?[] ? might_fault+0x68/0xbc > ?[] ? trace_hardirqs_off_thunk+0x3a/0x3c > ?[] sys32_waitpid+0xb/0xd > ?[] sysenter_dispatch+0x7/0x30 > ?[] ? trace_hardirqs_on_thunk+0x3a/0x3f > > I don't think it's related to the VFS patches, however, so I added > some other (maybe relevant) CCs too. > > At the time I was simply invoking gcc from bash. > > > Vegard > > * git://git.kernel.org/pub/scm/linux/kernel/git/npiggin/linux-npiggin.git > branch vfs-scale -- 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/