Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757410Ab0DOH3l (ORCPT ); Thu, 15 Apr 2010 03:29:41 -0400 Received: from casper.infradead.org ([85.118.1.10]:49115 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757384Ab0DOH3e (ORCPT ); Thu, 15 Apr 2010 03:29:34 -0400 Subject: Re: INFO: suspicious rcu_dereference_check() usage - include/linux/cgroup.h:492 invoked rcu_dereference_check() without protection! From: Peter Zijlstra To: Eric Paris Cc: paulmck@linux.vnet.ibm.com, Miles Lane , LKML In-Reply-To: <1271098032.4807.137.camel@twins> References: <20100311032843.GE6767@linux.vnet.ibm.com> <1271098032.4807.137.camel@twins> Content-Type: text/plain; charset="UTF-8" Date: Wed, 14 Apr 2010 12:47:38 +0200 Message-ID: <1271242058.32749.19.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2988 Lines: 78 On Mon, 2010-04-12 at 20:47 +0200, Peter Zijlstra wrote: > On Mon, 2010-04-12 at 14:44 -0400, Eric Paris wrote: > > On Wed, Mar 10, 2010 at 11:28 PM, Paul E. McKenney > > wrote: > > > I know you indicated this was fixed in mainline and I see that set of > > commits objects, but I'm seeing the below spew from linux-next today. > > > > tree: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git > > tag: next-20100412 > > commit: bbeecf185fe464ccd7ee97ce6d3646ad686995b4 > > > > [ 0.035602] =================================================== > > [ 0.036003] [ INFO: suspicious rcu_dereference_check() usage. ] > > [ 0.037006] --------------------------------------------------- > > [ 0.038004] include/linux/cgroup.h:533 invoked > > rcu_dereference_check() without protection! > > [ 0.039003] > > [ 0.039004] other info that might help us debug this: > > [ 0.039004] > > [ 0.040003] > > [ 0.040004] rcu_scheduler_active = 1, debug_locks = 0 > > [ 0.041004] no locks held by swapper/0. > > [ 0.042003] > > [ 0.042004] stack backtrace: > > [ 0.043005] Pid: 0, comm: swapper Not tainted 2.6.34-rc3-next-20100412+ #65 > > [ 0.044003] Call Trace: > > [ 0.045015] [] lockdep_rcu_dereference+0xaf/0xc0 > > [ 0.046010] [] set_task_cpu+0x2d2/0x370 > > Oh, right, I still have to sort that out. > > I need to figure out how all that scheduler and cgroup muck interact to > fix this. I think the below should cure this.. Signed-off-by: Peter Zijlstra --- kernel/sched.c | 10 ++++++++++ 1 files changed, 10 insertions(+), 0 deletions(-) diff --git a/kernel/sched.c b/kernel/sched.c index 3acf694..2e06d87 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -323,6 +323,15 @@ static inline struct task_group *task_group(struct task_struct *p) /* Change a task's cfs_rq and parent entity if it moves across CPUs/groups */ static inline void set_task_rq(struct task_struct *p, unsigned int cpu) { + /* + * Strictly speaking this rcu_read_lock() is not needed since the + * task_group is tied to the cgroup, which in turn can never go away + * as long as there are tasks attached to it. + * + * However since task_group() uses task_subsys_state() which is an + * rcu_dereference() user, this quiets CONFIG_PROVE_RCU. + */ + rcu_read_lock(); #ifdef CONFIG_FAIR_GROUP_SCHED p->se.cfs_rq = task_group(p)->cfs_rq[cpu]; p->se.parent = task_group(p)->se[cpu]; @@ -332,6 +341,7 @@ static inline void set_task_rq(struct task_struct *p, unsigned int cpu) p->rt.rt_rq = task_group(p)->rt_rq[cpu]; p->rt.parent = task_group(p)->rt_se[cpu]; #endif + rcu_read_unlock(); } #else -- 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/