From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754130Ab0AECDS (ORCPT ); Mon, 4 Jan 2010 21:03:18 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753640Ab0AECDR (ORCPT ); Mon, 4 Jan 2010 21:03:17 -0500 Received: from relay4-v.mail.gandi.net ([217.70.178.78]:53707 "EHLO relay4-v.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753484Ab0AECDQ (ORCPT ); Mon, 4 Jan 2010 21:03:16 -0500 Date: Mon, 4 Jan 2010 18:03:08 -0800 From: Josh Triplett To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, dvhltc@us.ibm.com, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com Subject: Re: [PATCH tip/core/rcu 2/3] rcu: add debug check for too many rcu_read_unlock() Message-ID: <20100105020307.GB11286@feather> References: <20100105000337.GA23307@linux.vnet.ibm.com> <12626498423064-git-send-email-> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <12626498423064-git-send-email-> 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 Mon, Jan 04, 2010 at 04:04:01PM -0800, Paul E. McKenney wrote: > From: Paul E. McKenney > > TREE_PREEMPT_RCU maintains an rcu_read_lock_nesting counter in the > task structure, which happens to be a signed int. So this patch adds a > check for this counter being negative at the end of __rcu_read_unlock(). > This check is under CONFIG_PROVE_LOCKING, so can be thought of as being > part of lockdep. > > Signed-off-by: Paul E. McKenney > --- > kernel/rcutree_plugin.h | 3 +++ > 1 files changed, 3 insertions(+), 0 deletions(-) > > diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h > index f11ebd4..e77cdf3 100644 > --- a/kernel/rcutree_plugin.h > +++ b/kernel/rcutree_plugin.h > @@ -304,6 +304,9 @@ void __rcu_read_unlock(void) > if (--ACCESS_ONCE(t->rcu_read_lock_nesting) == 0 && > unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) > rcu_read_unlock_special(t); > +#ifdef CONFIG_PROVE_LOCKING > + WARN_ON_ONCE(ACCESS_ONCE(t->rcu_read_lock_nesting) < 0); > +#endif /* #ifdef CONFIG_PROVE_LOCKING */ > } > EXPORT_SYMBOL_GPL(__rcu_read_unlock); Given that you *already* need to access t->rcu_read_lock_nesting here, why not just do the test all the time? Ideally you could access t->rcu_read_lock_nesting once, decrement it, and test for both 0 and negative. - Josh Triplett