From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758454Ab1EBWV6 (ORCPT ); Mon, 2 May 2011 18:21:58 -0400 Received: from e4.ny.us.ibm.com ([32.97.182.144]:41470 "EHLO e4.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754040Ab1EBWV5 (ORCPT ); Mon, 2 May 2011 18:21:57 -0400 Date: Mon, 2 May 2011 15:21:47 -0700 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, patches@linaro.org Subject: Re: [PATCH tip/core/rcu 45/86] net,act_police,rcu: remove rcu_barrier() Message-ID: <20110502222147.GL2294@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20110501132142.GA25494@linux.vnet.ibm.com> <1304256126-26015-45-git-send-email-paulmck@linux.vnet.ibm.com> <20110501155935.GH14829@feather> <20110502083618.GB2297@linux.vnet.ibm.com> <20110502175011.GC24574@feather> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110502175011.GC24574@feather> 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, May 02, 2011 at 10:50:11AM -0700, Josh Triplett wrote: > On Mon, May 02, 2011 at 01:36:18AM -0700, Paul E. McKenney wrote: > > On Sun, May 01, 2011 at 08:59:35AM -0700, Josh Triplett wrote: > > > On Sun, May 01, 2011 at 06:21:25AM -0700, Paul E. McKenney wrote: > > > > From: Lai Jiangshan > > > > > > > > There is no callback of this module maybe queued > > > > since we use kfree_rcu(), we can safely remove the rcu_barrier(). > > > > > > > > Signed-off-by: Lai Jiangshan > > > > Acked-by: David S. Miller > > > > Signed-off-by: Paul E. McKenney > > > > --- > > > > net/sched/act_police.c | 1 - > > > > 1 files changed, 0 insertions(+), 1 deletions(-) > > > > > > > > diff --git a/net/sched/act_police.c b/net/sched/act_police.c > > > > index d6bcd64..b3b9b32 100644 > > > > --- a/net/sched/act_police.c > > > > +++ b/net/sched/act_police.c > > > > @@ -396,7 +396,6 @@ static void __exit > > > > police_cleanup_module(void) > > > > { > > > > tcf_unregister_action(&act_police_ops); > > > > - rcu_barrier(); /* Wait for completion of call_rcu()'s (tcf_police_free_rcu) */ > > > > } > > > > > > Very nice side-effect of having common callback code. Seems worth doing > > > a review of other callers of rcu_barrier as well, to see if they still > > > need to do so. > > > > Agreed, and good point on the review. /me wonders how this review could > > be automated... > > Build everything as a module, and for each module check whether it uses > the symbol rcu_barrier but not the symbol call_rcu. Same for the > corresponding call_rcu_sched and call_rcu_bh. Good point -- I will give this a shot when I find AC power. > Also, Coccinelle could likely handle simple cases of > call_rcu(function_that_calls_container_of_then_kfree), at least when > the call and the function appear in the same source file. Good point -- it wasn't too hard by hand this time, but it would be a good addition to RCU checking. Thanx, Paul