From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Fri, 20 Apr 2018 18:13:11 +0200
Subject: [PATCH] rtmutex: annotate sleeping lock context

The RCU code complains on schedule() within a rcu_readlock() section.
The valid scenario on -RT is if a sleeping is held. In order to suppress
the warning the mirgrate_disable counter was used to identify the
invocation of schedule() due to lock contention.

Grygorii Strashko report that during CPU hotplug we might see the
warning via
 rt_spin_lock() -> migrate_disable() -> pin_current_cpu() -> __read_rt_lock()

because the counter is not yet set.
It is also possible to trigger the warning from cpu_chill()
(seen on a kblockd_mod_delayed_work_on() caller).

To address this RCU warning I annotate the sleeping lock context. The
counter is incremented before migrate_disable() so the warning Grygorii
should not trigger anymore. Additionally I use that counter in
cpu_chill() to avoid the RCU warning from there.

Reported-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 include/linux/sched.h      |   20 ++++++++++++++++++++
 kernel/locking/rtmutex.c   |   12 ++++++++++--
 kernel/locking/rwlock-rt.c |   18 ++++++++++++++----
 kernel/rcu/tree_plugin.h   |    8 ++++----
 4 files changed, 48 insertions(+), 10 deletions(-)

--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -611,6 +611,9 @@ struct task_struct {
 	int				migrate_disable_atomic;
 # endif
 #endif
+#ifdef CONFIG_PREEMPT_RT_FULL
+	int				sleeping_lock;
+#endif
 
 #ifdef CONFIG_PREEMPT_RCU
 	int				rcu_read_lock_nesting;
@@ -1731,6 +1734,23 @@ static __always_inline bool need_resched
 	return unlikely(tif_need_resched());
 }
 
+#ifdef CONFIG_PREEMPT_RT_FULL
+static inline void sleeping_lock_inc(void)
+{
+	current->sleeping_lock++;
+}
+
+static inline void sleeping_lock_dec(void)
+{
+	current->sleeping_lock--;
+}
+
+#else
+
+static inline void sleeping_lock_inc(void) { }
+static inline void sleeping_lock_dec(void) { }
+#endif
+
 /*
  * Wrappers for p->thread_info->cpu access. No-op on UP.
  */
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -1141,6 +1141,7 @@ void __sched rt_spin_lock_slowunlock(str
 
 void __lockfunc rt_spin_lock(spinlock_t *lock)
 {
+	sleeping_lock_inc();
 	migrate_disable();
 	spin_acquire(&lock->dep_map, 0, 0, _RET_IP_);
 	rt_spin_lock_fastlock(&lock->lock, rt_spin_lock_slowlock);
@@ -1155,6 +1156,7 @@ void __lockfunc __rt_spin_lock(struct rt
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 void __lockfunc rt_spin_lock_nested(spinlock_t *lock, int subclass)
 {
+	sleeping_lock_inc();
 	migrate_disable();
 	spin_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
 	rt_spin_lock_fastlock(&lock->lock, rt_spin_lock_slowlock);
@@ -1168,6 +1170,7 @@ void __lockfunc rt_spin_unlock(spinlock_
 	spin_release(&lock->dep_map, 1, _RET_IP_);
 	rt_spin_lock_fastunlock(&lock->lock, rt_spin_lock_slowunlock);
 	migrate_enable();
+	sleeping_lock_dec();
 }
 EXPORT_SYMBOL(rt_spin_unlock);
 
@@ -1193,12 +1196,15 @@ int __lockfunc rt_spin_trylock(spinlock_
 {
 	int ret;
 
+	sleeping_lock_inc();
 	migrate_disable();
 	ret = __rt_mutex_trylock(&lock->lock);
-	if (ret)
+	if (ret) {
 		spin_acquire(&lock->dep_map, 0, 1, _RET_IP_);
-	else
+	} else {
 		migrate_enable();
+		sleeping_lock_dec();
+	}
 	return ret;
 }
 EXPORT_SYMBOL(rt_spin_trylock);
@@ -1210,6 +1216,7 @@ int __lockfunc rt_spin_trylock_bh(spinlo
 	local_bh_disable();
 	ret = __rt_mutex_trylock(&lock->lock);
 	if (ret) {
+		sleeping_lock_inc();
 		migrate_disable();
 		spin_acquire(&lock->dep_map, 0, 1, _RET_IP_);
 	} else
@@ -1225,6 +1232,7 @@ int __lockfunc rt_spin_trylock_irqsave(s
 	*flags = 0;
 	ret = __rt_mutex_trylock(&lock->lock);
 	if (ret) {
+		sleeping_lock_inc();
 		migrate_disable();
 		spin_acquire(&lock->dep_map, 0, 1, _RET_IP_);
 	}
--- a/kernel/locking/rwlock-rt.c
+++ b/kernel/locking/rwlock-rt.c
@@ -305,12 +305,15 @@ int __lockfunc rt_read_trylock(rwlock_t
 {
 	int ret;
 
+	sleeping_lock_inc();
 	migrate_disable();
 	ret = do_read_rt_trylock(rwlock);
-	if (ret)
+	if (ret) {
 		rwlock_acquire_read(&rwlock->dep_map, 0, 1, _RET_IP_);
-	else
+	} else {
 		migrate_enable();
+		sleeping_lock_dec();
+	}
 	return ret;
 }
 EXPORT_SYMBOL(rt_read_trylock);
@@ -319,18 +322,22 @@ int __lockfunc rt_write_trylock(rwlock_t
 {
 	int ret;
 
+	sleeping_lock_inc();
 	migrate_disable();
 	ret = do_write_rt_trylock(rwlock);
-	if (ret)
+	if (ret) {
 		rwlock_acquire(&rwlock->dep_map, 0, 1, _RET_IP_);
-	else
+	} else {
 		migrate_enable();
+		sleeping_lock_dec();
+	}
 	return ret;
 }
 EXPORT_SYMBOL(rt_write_trylock);
 
 void __lockfunc rt_read_lock(rwlock_t *rwlock)
 {
+	sleeping_lock_inc();
 	migrate_disable();
 	rwlock_acquire_read(&rwlock->dep_map, 0, 0, _RET_IP_);
 	do_read_rt_lock(rwlock);
@@ -339,6 +346,7 @@ EXPORT_SYMBOL(rt_read_lock);
 
 void __lockfunc rt_write_lock(rwlock_t *rwlock)
 {
+	sleeping_lock_inc();
 	migrate_disable();
 	rwlock_acquire(&rwlock->dep_map, 0, 0, _RET_IP_);
 	do_write_rt_lock(rwlock);
@@ -350,6 +358,7 @@ void __lockfunc rt_read_unlock(rwlock_t
 	rwlock_release(&rwlock->dep_map, 1, _RET_IP_);
 	do_read_rt_unlock(rwlock);
 	migrate_enable();
+	sleeping_lock_dec();
 }
 EXPORT_SYMBOL(rt_read_unlock);
 
@@ -358,6 +367,7 @@ void __lockfunc rt_write_unlock(rwlock_t
 	rwlock_release(&rwlock->dep_map, 1, _RET_IP_);
 	do_write_rt_unlock(rwlock);
 	migrate_enable();
+	sleeping_lock_dec();
 }
 EXPORT_SYMBOL(rt_write_unlock);
 
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -325,13 +325,13 @@ static void rcu_preempt_note_context_swi
 	struct task_struct *t = current;
 	struct rcu_data *rdp;
 	struct rcu_node *rnp;
-	int mg_counter = 0;
+	int sleeping_l = 0;
 
 	lockdep_assert_irqs_disabled();
-#if defined(CONFIG_PREEMPT_RT_BASE)
-	mg_counter = t->migrate_disable;
+#if defined(CONFIG_PREEMPT_RT_FULL)
+	sleeping_l = t->sleeping_lock;
 #endif
-	WARN_ON_ONCE(!preempt && t->rcu_read_lock_nesting > 0 && !mg_counter);
+	WARN_ON_ONCE(!preempt && t->rcu_read_lock_nesting > 0 && !sleeping_l);
 	if (t->rcu_read_lock_nesting > 0 &&
 	    !t->rcu_read_unlock_special.b.blocked) {