locking/local_lock: Introduce local_lock_is_locked().

Introduce local_lock_is_locked() that returns true when
given local_lock is locked by current cpu (in !PREEMPT_RT) or
by current task (in PREEMPT_RT).
The goal is to detect a deadlock by the caller.

Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

Author: Alexei Starovoitov

include/linux/local_lock.h

@@ -66,6 +66,8 @@
  */
 #define local_trylock(lock)		__local_trylock(this_cpu_ptr(lock))
 
+#define local_lock_is_locked(lock)	__local_lock_is_locked(lock)
+
 /**
  * local_trylock_irqsave - Try to acquire a per CPU local lock, save and disable
  *			   interrupts if acquired

include/linux/local_lock_internal.h

@@ -165,6 +165,9 @@ do {								\
 		!!tl;						\
 	})
 
+/* preemption or migration must be disabled before calling __local_lock_is_locked */
+#define __local_lock_is_locked(lock) READ_ONCE(this_cpu_ptr(lock)->acquired)
+
 #define __local_lock_release(lock)					\
 	do {								\
 		local_trylock_t *tl;					\
@@ -285,4 +288,8 @@ do {								\
 		__local_trylock(lock);				\
 	})
 
+/* migration must be disabled before calling __local_lock_is_locked */
+#define __local_lock_is_locked(__lock)					\
+	(rt_mutex_owner(&this_cpu_ptr(__lock)->lock) == current)
+
 #endif /* CONFIG_PREEMPT_RT */

include/linux/rtmutex.h

@@ -44,6 +44,16 @@ static inline bool rt_mutex_base_is_locked(struct rt_mutex_base *lock)
 	return READ_ONCE(lock->owner) != NULL;
 }
 
+#ifdef CONFIG_RT_MUTEXES
+#define RT_MUTEX_HAS_WAITERS	1UL
+
+static inline struct task_struct *rt_mutex_owner(struct rt_mutex_base *lock)
+{
+	unsigned long owner = (unsigned long) READ_ONCE(lock->owner);
+
+	return (struct task_struct *) (owner & ~RT_MUTEX_HAS_WAITERS);
+}
+#endif
 extern void rt_mutex_base_init(struct rt_mutex_base *rtb);
 
 /**

kernel/locking/rtmutex_common.h

@@ -153,15 +153,6 @@ static inline struct rt_mutex_waiter *task_top_pi_waiter(struct task_struct *p)
 			pi_tree.entry);
 }
 
-#define RT_MUTEX_HAS_WAITERS	1UL
-
-static inline struct task_struct *rt_mutex_owner(struct rt_mutex_base *lock)
-{
-	unsigned long owner = (unsigned long) READ_ONCE(lock->owner);
-
-	return (struct task_struct *) (owner & ~RT_MUTEX_HAS_WAITERS);
-}
-
 /*
  * Constants for rt mutex functions which have a selectable deadlock
  * detection.