From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757323Ab2IGGzR (ORCPT ); Fri, 7 Sep 2012 02:55:17 -0400 Received: from casper.infradead.org ([85.118.1.10]:58057 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756189Ab2IGGzP convert rfc822-to-8bit (ORCPT ); Fri, 7 Sep 2012 02:55:15 -0400 Message-ID: <1347000873.18408.69.camel@twins> Subject: Re: [PATCH tip/core/rcu 01/15] rcu: Add PROVE_RCU_DELAY to provoke difficult races From: Peter Zijlstra To: paulmck@linux.vnet.ibm.com 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, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com, fweisbec@gmail.com, sbw@mit.edu, patches@linaro.org, "Paul E. McKenney" Date: Fri, 07 Sep 2012 08:54:33 +0200 In-Reply-To: <20120906205156.GZ2448@linux.vnet.ibm.com> References: <20120830185607.GA32148@linux.vnet.ibm.com> <1346352988-32444-1-git-send-email-paulmck@linux.vnet.ibm.com> <1346942312.18408.26.camel@twins> <20120906205156.GZ2448@linux.vnet.ibm.com> Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-Mailer: Evolution 3.2.2- Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2012-09-06 at 13:51 -0700, Paul E. McKenney wrote: > On Thu, Sep 06, 2012 at 04:38:32PM +0200, Peter Zijlstra wrote: > > On Thu, 2012-08-30 at 11:56 -0700, Paul E. McKenney wrote: > > > +#ifdef CONFIG_PROVE_RCU_DELAY > > > + udelay(10); /* Make preemption more probable. */ > > cond_resched(); /* for extra fun? */ > > The additional fun could include "scheduling while atomic", so I will > pass. ;-) > > (The problem is that __rcu_read_unlock() can be called with interrupts > disabled, among other things.) Hmm, too bad. Without a preemption point here you're relying on forced preemption, which of course can only happen on PREEMPT=y kernels. > > > +#endif /* #ifdef CONFIG_PROVE_RCU_DELAY */ > > > > >