From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751205Ab1IREJk (ORCPT ); Sun, 18 Sep 2011 00:09:40 -0400 Received: from mail-iy0-f174.google.com ([209.85.210.174]:36518 "EHLO mail-iy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750753Ab1IREJj (ORCPT ); Sun, 18 Sep 2011 00:09:39 -0400 Date: Sun, 18 Sep 2011 12:09:23 +0800 From: Yong Zhang To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, 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, "Paul E. McKenney" Subject: Re: [PATCH tip/core/rcu 41/55] rcu: Permit rt_mutex_unlock() with irqs disabled Message-ID: <20110918040923.GA2363@zhy> Reply-To: Yong Zhang References: <20110906180015.GA2560@linux.vnet.ibm.com> <1315332049-2604-41-git-send-email-paulmck@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <1315332049-2604-41-git-send-email-paulmck@linux.vnet.ibm.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 06, 2011 at 11:00:35AM -0700, Paul E. McKenney wrote: > From: Paul E. McKenney > > Create a separate lockdep class for the rt_mutex used for RCU priority > boosting and enable use of rt_mutex_lock() with irqs disabled. This > prevents RCU priority boosting from falling prey to deadlocks when > someone begins an RCU read-side critical section in preemptible state, > but releases it with an irq-disabled lock held. > > Unfortunately, the scheduler's runqueue and priority-inheritance locks > still must either completely enclose or be completely enclosed by any > overlapping RCU read-side critical section. > > Signed-off-by: Paul E. McKenney > Signed-off-by: Paul E. McKenney > --- > kernel/rcutree_plugin.h | 6 ++++++ > kernel/rtmutex.c | 8 ++++++++ > 2 files changed, 14 insertions(+), 0 deletions(-) > > diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h > index d3127e8..f6c63ea 100644 > --- a/kernel/rcutree_plugin.h > +++ b/kernel/rcutree_plugin.h > @@ -1149,6 +1149,8 @@ static void rcu_initiate_boost_trace(struct rcu_node *rnp) > > #endif /* #else #ifdef CONFIG_RCU_TRACE */ > > +static struct lock_class_key rcu_boost_class; > + > /* > * Carry out RCU priority boosting on the task indicated by ->exp_tasks > * or ->boost_tasks, advancing the pointer to the next task in the > @@ -1211,10 +1213,14 @@ static int rcu_boost(struct rcu_node *rnp) > */ > t = container_of(tb, struct task_struct, rcu_node_entry); > rt_mutex_init_proxy_locked(&mtx, t); > + /* Avoid lockdep false positives. This rt_mutex is its own thing. */ > + lockdep_set_class_and_name(&mtx.wait_lock, &rcu_boost_class, > + "rcu_boost_mutex"); > t->rcu_boost_mutex = &mtx; raw_spin_unlock_irqrestore(&rnp->lock, flags); <====A > rt_mutex_lock(&mtx); /* Side effect: boosts task t's priority. */ > rt_mutex_unlock(&mtx); /* Keep lockdep happy. */ > + local_irq_restore(flags); Does it help here? irq is enabled at A. So we still call rt_mutex_lock() with irq enabled. Seems should s/raw_spin_unlock_irqrestore/raw_spin_unlock ? BTW, since we are in process context, 'flags' is not needed to save, no? Thanks, Yong > > return rnp->exp_tasks != NULL || rnp->boost_tasks != NULL; > } > diff --git a/kernel/rtmutex.c b/kernel/rtmutex.c > index ab44911..2548f44 100644 > --- a/kernel/rtmutex.c > +++ b/kernel/rtmutex.c > @@ -579,6 +579,7 @@ __rt_mutex_slowlock(struct rt_mutex *lock, int state, > struct rt_mutex_waiter *waiter) > { > int ret = 0; > + int was_disabled; > > for (;;) { > /* Try to acquire the lock: */ > @@ -601,10 +602,17 @@ __rt_mutex_slowlock(struct rt_mutex *lock, int state, > > raw_spin_unlock(&lock->wait_lock); > > + was_disabled = irqs_disabled(); > + if (was_disabled) > + local_irq_enable(); > + > debug_rt_mutex_print_deadlock(waiter); > > schedule_rt_mutex(lock); > > + if (was_disabled) > + local_irq_disable(); > + > raw_spin_lock(&lock->wait_lock); > set_current_state(state); > } > -- > 1.7.3.2 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/