Commit 5342e269 authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Paul E. McKenney
Browse files

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.

This version removes a redundant local_irq_restore() noted by
Yong Zhang.

Signed-off-by: default avatarPaul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 06ae115a

kernel/rcutree_plugin.h

+5 −0
Original line number Diff line number Diff line
@@ -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
@@ -1211,6 +1213,9 @@ 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. */

kernel/rtmutex.c

+8 −0
Original line number Diff line number Diff line
@@ -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);

	}

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