locking/percpu-rwsem: Add percpu_is_write_locked() and percpu_is_read_locked()

Implement simple accessors to probe percpu-rwsem's locked state:
percpu_is_write_locked(), percpu_is_read_locked().

Signed-off-by: Marco Elver <[e-mail]>
Signed-off-by: Peter Zijlstra (Intel) <[e-mail]>
Reviewed-by: Dmitry Vyukov <[e-mail]>
Acked-by: Ian Rogers <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

include/linux/percpu-rwsem.h

···
 	preempt_enable();
 }
 
+extern bool percpu_is_read_locked(struct percpu_rw_semaphore *);
 extern void percpu_down_write(struct percpu_rw_semaphore *);
 extern void percpu_up_write(struct percpu_rw_semaphore *);
+
+static inline bool percpu_is_write_locked(struct percpu_rw_semaphore *sem)
+{
+	return atomic_read(&sem->block);
+}
 
 extern int __percpu_init_rwsem(struct percpu_rw_semaphore *,
 				const char *, struct lock_class_key *);

kernel/locking/percpu-rwsem.c

···
 	__sum;								\
 })
 
+bool percpu_is_read_locked(struct percpu_rw_semaphore *sem)
+{
+	return per_cpu_sum(*sem->read_count) != 0 && !atomic_read(&sem->block);
+}
+EXPORT_SYMBOL_GPL(percpu_is_read_locked);
+
 /*
  * Return true if the modular sum of the sem->read_count per-CPU variable is
  * zero.  If this sum is zero, then it is stable due to the fact that if any