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: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index d3127e8..2842276 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -1149,6 +1149,8 @@
#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 @@
*/
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. */
