From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755434AbaIQNKk (ORCPT ); Wed, 17 Sep 2014 09:10:40 -0400 Received: from e38.co.us.ibm.com ([32.97.110.159]:36856 "EHLO e38.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754831AbaIQNKi (ORCPT ); Wed, 17 Sep 2014 09:10:38 -0400 Date: Wed, 17 Sep 2014 06:10:13 -0700 From: "Paul E. McKenney" To: Lan Tianyu 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, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com, "Rafael J. Wysocki" Subject: Re: [PATCH RFC tip/core/rcu] Eliminate deadlock between CPU hotplug and expedited grace periods Message-ID: <20140917131013.GU4723@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20140828194745.GA3761@linux.vnet.ibm.com> <5419342E.60602@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <5419342E.60602@intel.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14091713-1344-0000-0000-0000044564CA Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 17, 2014 at 03:11:42PM +0800, Lan Tianyu wrote: > On 2014年08月29日 03:47, Paul E. McKenney wrote: > > Currently, the expedited grace-period primitives do get_online_cpus(). > > This greatly simplifies their implementation, but means that calls to > > them holding locks that are acquired by CPU-hotplug notifiers (to say > > nothing of calls to these primitives from CPU-hotplug notifiers) can > > deadlock. But this is starting to become inconvenient: > > https://lkml.org/lkml/2014/8/5/754 > > > > This commit avoids the deadlock and retains the simplicity by creating > > a try_get_online_cpus(), which returns false if the get_online_cpus() > > reference count could not immediately be incremented. If a call to > > try_get_online_cpus() returns true, the expedited primitives operate > > as before. If a call returns false, the expedited primitives fall back > > to normal grace-period operations. This falling back of course results > > in increased grace-period latency, but only during times when CPU > > hotplug operations are actually in flight. The effect should therefore > > be negligible during normal operation. > > > > Signed-off-by: Paul E. McKenney > > Cc: Josh Triplett > > Cc: "Rafael J. Wysocki" > > Cc: Lan Tianyu > > Hi Paul: > What's the status of the patch? Will you push it? Thanks. By default, it would go into 3.19. Do you need it earlier? Thanx, Paul