From 4b75ad090c9757c05a048b6e23bbf6d1110db73d Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 16 Aug 2011 17:46:46 -0700 Subject: [PATCH] rcu: Permit rt_mutex_unlock() with irqs disabled 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(+) diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index d3127e8764cb..f6c63eac72d4 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 ab449117aaf2..2548f4487eee 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); } -- 2.39.5