Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754577Ab1FGSLh (ORCPT ); Tue, 7 Jun 2011 14:11:37 -0400 Received: from e7.ny.us.ibm.com ([32.97.182.137]:50951 "EHLO e7.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751425Ab1FGSLg (ORCPT ); Tue, 7 Jun 2011 14:11:36 -0400 Date: Tue, 7 Jun 2011 11:11:31 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: "Nikunj A. Dadhania" , mingo@elte.hu, linux-kernel@vger.kernel.org Subject: Re: [PATCH] sched: remove rcu_read_lock from wake_affine Message-ID: <20110607181131.GD2286@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20110607101251.777.34547.stgit@IBM-009124035060.in.ibm.com> <1307442411.2322.246.camel@twins> <20110607172606.GA2286@linux.vnet.ibm.com> <1307467763.2322.282.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1307467763.2322.282.camel@twins> 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 Content-Length: 1648 Lines: 41 On Tue, Jun 07, 2011 at 07:29:23PM +0200, Peter Zijlstra wrote: > On Tue, 2011-06-07 at 10:26 -0700, Paul E. McKenney wrote: > > > > Nikunj, one such approach is is "WARN_ON_ONCE(!rcu_read_lock_held())". > > > > This will complain if this function is called without an rcu_read_lock() > > in effect, but only if CONFIG_PROVE_RCU=y. > > rcu_lockdep_assert(rcu_read_lock_held()) would be nicer, Good point! > however, since > the below: > > > > > static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync) > > > > { > > > > s64 this_load, load; > > > > @@ -1481,7 +1482,6 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync) > > > > * effect of the currently running task from the load > > > > * of the current CPU: > > > > */ > > > > - rcu_read_lock(); > > > > if (sync) { > > > > tg = task_group(current); > > > > weight = current->se.load.weight; > > task_group() has an rcu_dereference_check() in, its really not needed, > the thing will yell if we get this wrong. Fair enough! The main reason for adding it at this level as well is to prevent people from "fixing" splats by adding rcu_read_lock() and rcu_read_unlock() at this level. But you would see any such patch, so such a "fix" would not get far. ;-) Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/