[PATCH 1/2] sched: Introduce APIs for waiting multi events

[Lai Jiangshan <laijs@cn.fujitsu.com>]

Impact: make kernel has APIs for waiting multi events

Based on code in the RCU, the simple waiting-multi-events
algorithm may do not serve RCU only.

Introduce 5 APIs for waiting multi events

start scheduling events:  ref_completion_get_init()
schedule one event:       ref_completion_get()
end scheduling events:    ref_completion_put_init()

any event is finished:    ref_completion_put()

waiting scheduled events: ref_completion_wait()

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
---
diff --git a/include/linux/completion.h b/include/linux/completion.h
index 4a6b604..86c8236 100644
--- a/include/linux/completion.h
+++ b/include/linux/completion.h
@@ -8,6 +8,7 @@
  * See kernel/sched.c for details.
  */
 
+#include <asm/atomic.h>
 #include <linux/wait.h>
 
 /**
@@ -98,5 +99,44 @@ extern void complete_all(struct completion *);
  */
 #define INIT_COMPLETION(x)	((x).done = 0)
 
+/*
+ * wait all references are put, or wait multi events finished in other words
+ * ref_completion_get_init() called before the struct is used or reused.
+ * ref_completion_put_init() called after all ref_completion_get()s called.
+ * ref_completion_wait()     waiting until all ref_completion_put()s and
+ *                           the ref_completion_put_init() are called.
+ */
+struct ref_completion {
+	atomic_t ref;
+	struct completion wait;
+};
+
+static inline void ref_completion_get_init(struct ref_completion *rc)
+{
+	atomic_set(&rc->ref, 1);
+	init_completion(&rc->wait);
+}
+
+static inline void ref_completion_get(struct ref_completion *rc)
+{
+	atomic_inc(&rc->ref);
+}
+
+static inline void ref_completion_put(struct ref_completion *rc)
+{
+	if (atomic_dec_and_test(&rc->ref))
+		complete_all(&rc->wait);
+}
+
+static inline void ref_completion_put_init(struct ref_completion *rc)
+{
+	if (atomic_dec_and_test(&rc->ref))
+		complete_all(&rc->wait);
+}
+
+static inline void ref_completion_wait(struct ref_completion *rc)
+{
+	wait_for_completion(&rc->wait);
+}
 
 #endif