From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755982Ab1IGGZc (ORCPT ); Wed, 7 Sep 2011 02:25:32 -0400 Received: from e9.ny.us.ibm.com ([32.97.182.139]:46556 "EHLO e9.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755746Ab1IGGVC (ORCPT ); Wed, 7 Sep 2011 02:21:02 -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, "Paul E. McKenney" , "Paul E. McKenney" Subject: [PATCH tip/core/rcu 41/55] rcu: Permit rt_mutex_unlock() with irqs disabled Date: Tue, 6 Sep 2011 11:00:35 -0700 Message-Id: <1315332049-2604-41-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.7.3.2 In-Reply-To: <20110906180015.GA2560@linux.vnet.ibm.com> References: <20110906180015.GA2560@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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); rt_mutex_lock(&mtx); /* Side effect: boosts task t's priority. */ rt_mutex_unlock(&mtx); /* Keep lockdep happy. */ + local_irq_restore(flags); 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