percpu-refcount: Add EXPORT_SYMBOL to use percpu_ref from modules

This patch adds EXPORT_SYMBOL() for percpu_ref_init(),
percpu_ref_cancel_init() and percpu_ref_kill_and_confirm() so
that percpu refcounting can be used by external modules.

Cc: Kent Overstreet <kmo@daterainc.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

lib/percpu-refcount.c

@@ -53,6 +53,7 @@ int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release)
 	ref->release = release;
 	return 0;
 }
+EXPORT_SYMBOL(percpu_ref_init);
 
 /**
  * percpu_ref_cancel_init - cancel percpu_ref_init()
@@ -84,6 +85,7 @@ void percpu_ref_cancel_init(struct percpu_ref *ref)
 		free_percpu(ref->pcpu_count);
 	}
 }
+EXPORT_SYMBOL(percpu_ref_cancel_init);
 
 static void percpu_ref_kill_rcu(struct rcu_head *rcu)
 {
@@ -156,3 +158,4 @@ void percpu_ref_kill_and_confirm(struct percpu_ref *ref,
 
 	call_rcu_sched(&ref->rcu, percpu_ref_kill_rcu);
 }
+EXPORT_SYMBOL(percpu_ref_kill_and_confirm);