From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755061Ab2BBQ3Y (ORCPT ); Thu, 2 Feb 2012 11:29:24 -0500 Received: from e9.ny.us.ibm.com ([32.97.182.139]:53228 "EHLO e9.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752488Ab2BBQ3W (ORCPT ); Thu, 2 Feb 2012 11:29:22 -0500 Date: Thu, 2 Feb 2012 08:27:55 -0800 From: "Paul E. McKenney" To: Josh Triplett 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: <20120202162755.GJ2518@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com 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> <20120202010146.GF29058@leaf> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120202010146.GF29058@leaf> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12020216-7182-0000-0000-000000A689EE Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 01, 2012 at 05:01:46PM -0800, Josh Triplett wrote: > On Wed, Feb 01, 2012 at 11:41:22AM -0800, Paul E. McKenney wrote: > > From: "Paul E. McKenney" > > > > 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. > > > > Signed-off-by: Paul E. McKenney > > Signed-off-by: Paul E. McKenney > > --- > > kernel/rcutree.c | 1 + > > 1 files changed, 1 insertions(+), 0 deletions(-) > > > > diff --git a/kernel/rcutree.c b/kernel/rcutree.c > > index d0f8e64..4655f3e 100644 > > --- 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! */ > > debug_rcu_head_queue(head); > > Upon further checking: > > static inline void debug_rcu_head_queue(struct rcu_head *head) > { > WARN_ON_ONCE((unsigned long)head & 0x3); > > :) Fair point! I guess that we really only need one of these. ;-) I have kept the unconditional one and removed the one hidden under CONFIG_DEBUG_OBJECTS_RCU_HEAD, but in a separate commit with your Reported-by. Thanx, Paul