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/rtmutex.c b/kernel/rtmutex.c
index 255e166..5e8d9cc 100644
--- a/kernel/rtmutex.c
+++ b/kernel/rtmutex.c
@@ -579,6 +579,7 @@
struct rt_mutex_waiter *waiter)
{
int ret = 0;
+ int was_disabled;
for (;;) {
/* Try to acquire the lock: */
@@ -601,10 +602,17 @@
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);
}