From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754307Ab2BBULd (ORCPT ); Thu, 2 Feb 2012 15:11:33 -0500 Received: from relay4-d.mail.gandi.net ([217.70.183.196]:34587 "EHLO relay4-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753376Ab2BBULb (ORCPT ); Thu, 2 Feb 2012 15:11:31 -0500 X-Originating-IP: 217.70.178.130 X-Originating-IP: 50.43.15.19 Date: Thu, 2 Feb 2012 12:11:18 -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, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com, fweisbec@gmail.com, patches@linaro.org, "Paul E. McKenney" Subject: Re: [PATCH RFC tip/core/rcu 04/41] rcu: Add diagnostic for misaligned rcu_head structures Message-ID: <20120202201117.GC9279@leaf> References: <20120201194131.GA10028@linux.vnet.ibm.com> <1328125319-5205-1-git-send-email-paulmck@linux.vnet.ibm.com> <1328125319-5205-4-git-send-email-paulmck@linux.vnet.ibm.com> <20120202010026.GE29058@leaf> <20120202162235.GI2518@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120202162235.GI2518@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 02, 2012 at 08:22:35AM -0800, Paul E. McKenney wrote: > On Wed, Feb 01, 2012 at 05:00:26PM -0800, Josh Triplett wrote: > > On Wed, Feb 01, 2012 at 11:41:22AM -0800, Paul E. McKenney wrote: > > > The push for energy efficiency will require that RCU tag rcu_head > > > structures to indicate whether or not their invocation is time critical. > > > This tagging is best carried out in the bottom bits of the ->next > > > pointers in the rcu_head structures. This tagging requires that the > > > rcu_head structures be properly aligned, so this commit adds the required > > > diagnostics. > > > > > --- a/kernel/rcutree.c > > > +++ b/kernel/rcutree.c > > > @@ -1707,6 +1707,7 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), > > > unsigned long flags; > > > struct rcu_data *rdp; > > > > > > + WARN_ON_ONCE((unsigned long)head & 0x3); /* Misaligned rcu_head! */ > > > > I wonder if this should go out in one of the wrapper macros, so that the > > _ONCE means once per call site? > > Certainly past experience introducing lockdep-RCU would argue that way. ;-) > > However, my testing thus far (famous last words!) has found no > misalignments. So I expect that these will be caught as they are > inserted, so one at a time should be fine. Fair enough. Doesn't seem worth introducing a new wrapper macro for, then, since it doesn't look like an appropriate one currently exists. - Josh Triplett