From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756341AbZJGGQB (ORCPT ); Wed, 7 Oct 2009 02:16:01 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753445AbZJGGQB (ORCPT ); Wed, 7 Oct 2009 02:16:01 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:41834 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753166AbZJGGQA (ORCPT ); Wed, 7 Oct 2009 02:16:00 -0400 Date: Wed, 7 Oct 2009 08:14:48 +0200 From: Ingo Molnar To: "Paul E. McKenney" 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: <20091007061448.GA21673@elte.hu> References: <20091007044748.GA12763@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20091007044748.GA12763@linux.vnet.ibm.com> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.5 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * 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. Ingo