From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752552Ab1GTASf (ORCPT ); Tue, 19 Jul 2011 20:18:35 -0400 Received: from e5.ny.us.ibm.com ([32.97.182.145]:38070 "EHLO e5.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752279Ab1GTASd (ORCPT ); Tue, 19 Jul 2011 20:18:33 -0400 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: 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, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com, patches@linaro.org, greearb@candelatech.com, edt@aei.ca, "Paul E. McKenney" Subject: [PATCH tip/core/urgent 1/7] rcu: decrease rcu_report_exp_rnp coupling with scheduler Date: Tue, 19 Jul 2011 17:18:17 -0700 Message-Id: <1311121103-16978-1-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.7.3.2 In-Reply-To: <20110720001738.GA16369@linux.vnet.ibm.com> References: <20110720001738.GA16369@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org PREEMPT_RCU read-side critical sections blocking an expedited grace period invoke rcu_report_exp_rnp(). When the last such critical section has completed, rcu_report_exp_rnp() invokes the scheduler to wake up the task that invoked synchronize_rcu_expedited() -- needlessly holding the root rcu_node structure's lock while doing so, thus needlessly providing a way for RCU and the scheduler to deadlock. This commit therefore releases the root rcu_node structure's lock before calling wake_up(). Reported-by: Ed Tomlinson Signed-off-by: Paul E. McKenney --- kernel/rcutree_plugin.h | 3 ++- 1 files changed, 2 insertions(+), 1 deletions(-) diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 75113cb..94a674e 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -696,8 +696,10 @@ static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp) raw_spin_lock_irqsave(&rnp->lock, flags); for (;;) { if (!sync_rcu_preempt_exp_done(rnp)) + raw_spin_unlock_irqrestore(&rnp->lock, flags); break; if (rnp->parent == NULL) { + raw_spin_unlock_irqrestore(&rnp->lock, flags); wake_up(&sync_rcu_preempt_exp_wq); break; } @@ -707,7 +709,6 @@ static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp) raw_spin_lock(&rnp->lock); /* irqs already disabled */ rnp->expmask &= ~mask; } - raw_spin_unlock_irqrestore(&rnp->lock, flags); } /* -- 1.7.3.2