From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759167AbZJGNxR (ORCPT ); Wed, 7 Oct 2009 09:53:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758550AbZJGNxP (ORCPT ); Wed, 7 Oct 2009 09:53:15 -0400 Received: from e3.ny.us.ibm.com ([32.97.182.143]:48817 "EHLO e3.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756119AbZJGNxP (ORCPT ); Wed, 7 Oct 2009 09:53:15 -0400 Date: Wed, 7 Oct 2009 06:52:37 -0700 From: "Paul E. McKenney" To: Ingo Molnar Cc: linux-kernel@vger.kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, josh@joshtriplett.org, dvhltc@us.ibm.com, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com Subject: Re: [PATCH tip/core/rcu 0/3] rcu: prevent hangs by simplifying rcu_barrier/CPU-hotplug, fix lockdep complaint Message-ID: <20091007135236.GG6838@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20091007044748.GA12763@linux.vnet.ibm.com> <20091007061448.GA21673@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20091007061448.GA21673@elte.hu> User-Agent: Mutt/1.5.15+20070412 (2007-04-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 07, 2009 at 08:14:48AM +0200, Ingo Molnar wrote: > > * Paul E. McKenney wrote: > > > This patchset fixes a couple of issues with TREE_PREEMPT_RCU: > > > > 1. The current implementation of rcu_barrier() waits for any > > prior CPU-hotplug operation to complete. This code path has > > resulted in some hangs, so first move this code from rcupdate.c > > to rcutree.c and then use a simpler algorithm that avoids the > > waiting, eliminating the possibility of such hangs. > > > > 2. The lockdep facility complains from time to time due to the > > fact that certain combinations of CPU-hotplug operations can > > cause the TREE_PREEMPT_RCU code to acquire the root rcu_node > > structure's lock while holding a leaf rcu_node structure's > > lock. This patch places the root rcu_node structure's lock > > into its own lockdep class to prevent this false positive. > > > > Ingo, please rewind tip/core/rcu to commit #135c8aea before applying this > > series, as these patches really need to go into 2.6.32. Reworked and > > retested rcutiny (for 2.6.33, as Linus requested) will follow in a > > few days. Or more patches for more bug fixes, as the case may be. ;-) > > > > b/kernel/rcupdate.c | 120 ----------------------------------- > > b/kernel/rcutree.c | 120 +++++++++++++++++++++++++++++++++++ > > b/kernel/rcutree.h | 11 ++- > > b/kernel/rcutree_plugin.h | 34 ++++++++++ > > b/kernel/rcutree_trace.c | 5 - > > kernel/rcutree.c | 156 ++++++++++++++++++++++++---------------------- > > 6 files changed, 248 insertions(+), 198 deletions(-) > > Applied, thanks Paul! > > I dropped these commits for now: > > 3ffea79: rcu: Make hot-unplugged CPU relinquish its own RCU callbacks > eddd962: rcu: Move rcu_barrier() to rcutree, make lightweight rcu_barrier() for rcutiny > a39e7d5: rcu-tiny: The Bloatwatch Edition, v6 > > We can apply rcu-tiny for .33 again, once the dust has settled. Sounds good! I am placing rcu-tiny and synchronize_srcu_expedited() on a separate branch in my local git tree for 2.6.33. Thanx, Paul