From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754222AbaIAQRn (ORCPT ); Mon, 1 Sep 2014 12:17:43 -0400 Received: from casper.infradead.org ([85.118.1.10]:57904 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753822AbaIAQRm (ORCPT ); Mon, 1 Sep 2014 12:17:42 -0400 Date: Mon, 1 Sep 2014 18:17:35 +0200 From: Peter Zijlstra To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com, <""@rjwysocki.net>, tianyu.lan@intel.com Subject: Re: [PATCH RFC tip/core/rcu] Eliminate deadlock between CPU hotplug and expedited grace periods Message-ID: <20140901161735.GA5806@worktop.ger.corp.intel.com> References: <20140828194745.GA3761@linux.vnet.ibm.com> <20140901112059.GG27892@worktop.ger.corp.intel.com> <20140901160550.GL5001@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140901160550.GL5001@linux.vnet.ibm.com> User-Agent: Mutt/1.5.22.1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 01, 2014 at 09:05:50AM -0700, Paul E. McKenney wrote: > > URGH.. I really hate that. The hotplug interface is already too > > horrible, we should not add such hacks to it. > > We do have try_ interfaces to a number of other subsystems, so I don't > believe that it qualifies as such a hack. We do indeed, but I'm not sure about adding this to the hotplug stuff. Also; not really understanding the problem doesn't help. > > How about ripping that rcu_expedited stuff out instead? That's all > > conditional anyhow, so might as well not do it. > > In what way is the expedited stuff conditional? synchronize_sched() conditionally calls synchronize_sched_expedited() and its condition: rcu_expedited, gets set/cleared on pm notifiers and nr_cpu_ids.