[PATCH RT] locking: Make spinlock_t and rwlock_t a RCU section on RT

[Sebastian Andrzej Siewior]

On !RT a locked spinlock_t and rwlock_t disables preemption which
implies a RCU read section. There is code that relies on that behaviour.

Add an explicit RCU read section on RT while a sleeping lock (a lock
which would disables preemption on !RT) acquired.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
---
 kernel/locking/rtmutex.c   | 6 ++++++
 kernel/locking/rwlock-rt.c | 6 ++++++
 2 files changed, 12 insertions(+)

diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index cf09f8e7ed0f4..602eb7821a1b1 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -1141,6 +1141,7 @@ void __sched rt_spin_lock_slowunlock(struct rt_mutex *lock)
 void __lockfunc rt_spin_lock(spinlock_t *lock)
 {
 	sleeping_lock_inc();
+	rcu_read_lock();
 	migrate_disable();
 	spin_acquire(&lock->dep_map, 0, 0, _RET_IP_);
 	rt_spin_lock_fastlock(&lock->lock, rt_spin_lock_slowlock);
@@ -1156,6 +1157,7 @@ void __lockfunc __rt_spin_lock(struct rt_mutex *lock)
 void __lockfunc rt_spin_lock_nested(spinlock_t *lock, int subclass)
 {
 	sleeping_lock_inc();
+	rcu_read_lock();
 	migrate_disable();
 	spin_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
 	rt_spin_lock_fastlock(&lock->lock, rt_spin_lock_slowlock);
@@ -1169,6 +1171,7 @@ void __lockfunc rt_spin_unlock(spinlock_t *lock)
 	spin_release(&lock->dep_map, 1, _RET_IP_);
 	rt_spin_lock_fastunlock(&lock->lock, rt_spin_lock_slowunlock);
 	migrate_enable();
+	rcu_read_unlock();
 	sleeping_lock_dec();
 }
 EXPORT_SYMBOL(rt_spin_unlock);
@@ -1200,6 +1203,7 @@ int __lockfunc rt_spin_trylock(spinlock_t *lock)
 	ret = __rt_mutex_trylock(&lock->lock);
 	if (ret) {
 		spin_acquire(&lock->dep_map, 0, 1, _RET_IP_);
+		rcu_read_lock();
 	} else {
 		migrate_enable();
 		sleeping_lock_dec();
@@ -1216,6 +1220,7 @@ int __lockfunc rt_spin_trylock_bh(spinlock_t *lock)
 	ret = __rt_mutex_trylock(&lock->lock);
 	if (ret) {
 		sleeping_lock_inc();
+		rcu_read_lock();
 		migrate_disable();
 		spin_acquire(&lock->dep_map, 0, 1, _RET_IP_);
 	} else
@@ -1232,6 +1237,7 @@ int __lockfunc rt_spin_trylock_irqsave(spinlock_t *lock, unsigned long *flags)
 	ret = __rt_mutex_trylock(&lock->lock);
 	if (ret) {
 		sleeping_lock_inc();
+		rcu_read_lock();
 		migrate_disable();
 		spin_acquire(&lock->dep_map, 0, 1, _RET_IP_);
 	}
diff --git a/kernel/locking/rwlock-rt.c b/kernel/locking/rwlock-rt.c
index c3b91205161cc..0ae8c62ea8320 100644
--- a/kernel/locking/rwlock-rt.c
+++ b/kernel/locking/rwlock-rt.c
@@ -310,6 +310,7 @@ int __lockfunc rt_read_trylock(rwlock_t *rwlock)
 	ret = do_read_rt_trylock(rwlock);
 	if (ret) {
 		rwlock_acquire_read(&rwlock->dep_map, 0, 1, _RET_IP_);
+		rcu_read_lock();
 	} else {
 		migrate_enable();
 		sleeping_lock_dec();
@@ -327,6 +328,7 @@ int __lockfunc rt_write_trylock(rwlock_t *rwlock)
 	ret = do_write_rt_trylock(rwlock);
 	if (ret) {
 		rwlock_acquire(&rwlock->dep_map, 0, 1, _RET_IP_);
+		rcu_read_lock();
 	} else {
 		migrate_enable();
 		sleeping_lock_dec();
@@ -338,6 +340,7 @@ EXPORT_SYMBOL(rt_write_trylock);
 void __lockfunc rt_read_lock(rwlock_t *rwlock)
 {
 	sleeping_lock_inc();
+	rcu_read_lock();
 	migrate_disable();
 	rwlock_acquire_read(&rwlock->dep_map, 0, 0, _RET_IP_);
 	do_read_rt_lock(rwlock);
@@ -347,6 +350,7 @@ EXPORT_SYMBOL(rt_read_lock);
 void __lockfunc rt_write_lock(rwlock_t *rwlock)
 {
 	sleeping_lock_inc();
+	rcu_read_lock();
 	migrate_disable();
 	rwlock_acquire(&rwlock->dep_map, 0, 0, _RET_IP_);
 	do_write_rt_lock(rwlock);
@@ -358,6 +362,7 @@ void __lockfunc rt_read_unlock(rwlock_t *rwlock)
 	rwlock_release(&rwlock->dep_map, 1, _RET_IP_);
 	do_read_rt_unlock(rwlock);
 	migrate_enable();
+	rcu_read_unlock();
 	sleeping_lock_dec();
 }
 EXPORT_SYMBOL(rt_read_unlock);
@@ -367,6 +372,7 @@ void __lockfunc rt_write_unlock(rwlock_t *rwlock)
 	rwlock_release(&rwlock->dep_map, 1, _RET_IP_);
 	do_write_rt_unlock(rwlock);
 	migrate_enable();
+	rcu_read_unlock();
 	sleeping_lock_dec();
 }
 EXPORT_SYMBOL(rt_write_unlock);
-- 
2.24.0