From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756191Ab0DNPnJ (ORCPT ); Wed, 14 Apr 2010 11:43:09 -0400 Received: from e1.ny.us.ibm.com ([32.97.182.141]:41950 "EHLO e1.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756094Ab0DNPnH (ORCPT ); Wed, 14 Apr 2010 11:43:07 -0400 Date: Wed, 14 Apr 2010 08:43:02 -0700 From: "Paul E. McKenney" To: Lai Jiangshan Cc: David Miller , fweisbec@gmail.com, a.p.zijlstra@chello.nl, mingo@elte.hu, sparclinux@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: Weird rcu lockdep warning Message-ID: <20100414154302.GC2516@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20100413200432.GB5099@nowhere> <20100413234043.GG2538@linux.vnet.ibm.com> <20100414000226.GH5602@nowhere> <20100413.171306.25868761.davem@davemloft.net> <20100414014930.GI2538@linux.vnet.ibm.com> <4BC537C9.8050600@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4BC537C9.8050600@cn.fujitsu.com> 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 Wed, Apr 14, 2010 at 11:34:33AM +0800, Lai Jiangshan wrote: > Paul E. McKenney wrote: > > On Tue, Apr 13, 2010 at 05:13:06PM -0700, David Miller wrote: > >> From: Frederic Weisbecker > >> Date: Wed, 14 Apr 2010 02:02:27 +0200 > >> > >>> I just have a guess though.... > >>> This seems to always happen from NMI path, and lockdep is disabled on NMI. > >>> I suspect the lock_acquire() performed by rcu_read_lock() is just ignored > >>> and then the rcu_read_lock_held() check has the wrong result... > >> Yeah, I bet that's it too. > >> > >> lock_is_held() can't return anything meaningful while lockdep is > >> disabled, which it is during NMIs. > > > > Ah! So I just need to add a "current->lockdep_recursion" > > check to debug_lockdep_rcu_enabled(). And move the function to > > kernel/rcutree_plugin.h to avoid #include hell. > > > > See below for (untested) patch. > > > > Thanx, Paul > > > > ------------------------------------------------------------------------ > > > > include/linux/rcupdate.h | 5 +---- > > kernel/rcutree_plugin.h | 11 +++++++++++ > > 2 files changed, 12 insertions(+), 4 deletions(-) > > > > commit 304d8da6cd791a81ce3164f867e1b3ef4f9af1d1 > > Author: Paul E. McKenney > > Date: Tue Apr 13 18:45:51 2010 -0700 > > > > rcu: Make RCU lockdep check the lockdep_recursion variable > > > > The lockdep facility temporarily disables lockdep checking by incrementing > > the current->lockdep_recursion variable. Such disabling happens in NMIs > > and in other situations where lockdep might expect to recurse on itself. > > This patch therefore checks current->lockdep_recursion, disabling RCU > > lockdep splats when this variable is non-zero. > > > > Reported-by: Frederic Weisbecker > > Reported-by: David Miller > > Signed-off-by: Paul E. McKenney > > > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > > index 9f1ddfe..07db2fe 100644 > > --- a/include/linux/rcupdate.h > > +++ b/include/linux/rcupdate.h > > @@ -101,10 +101,7 @@ extern struct lockdep_map rcu_sched_lock_map; > > # define rcu_read_release_sched() \ > > lock_release(&rcu_sched_lock_map, 1, _THIS_IP_) > > > > -static inline int debug_lockdep_rcu_enabled(void) > > -{ > > - return likely(rcu_scheduler_active && debug_locks); > > -} > > +extern int debug_lockdep_rcu_enabled(void); > > > > /** > > * rcu_read_lock_held - might we be in RCU read-side critical section? > > diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h > > index 79b53bd..2169abe 100644 > > --- a/kernel/rcutree_plugin.h > > +++ b/kernel/rcutree_plugin.h > > @@ -1067,3 +1067,14 @@ static void rcu_needs_cpu_flush(void) > > } > > > > #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */ > > + > > +#ifdef CONFIG_DEBUG_LOCK_ALLOC > > + > > +int debug_lockdep_rcu_enabled(void) > > +{ > > + return likely(rcu_scheduler_active && > > + debug_locks && > > + current->lockdep_recursion == 0); > > +} > > + > > Looks good to me too, but I think > 'likely' is needless since the function is not inline. Good point. And to add injury to insult, I forgot EXPORT_SYMBOL_GPL(). Updated patch in the works. Thanx, Paul