closures: closure_nr_remaining()

Factor out a new helper, which returns the number of events outstanding.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

include/linux/closure.h

@@ -172,6 +172,11 @@ void __closure_wake_up(struct closure_waitlist *list);
 bool closure_wait(struct closure_waitlist *list, struct closure *cl);
 void __closure_sync(struct closure *cl);
 
+static inline unsigned closure_nr_remaining(struct closure *cl)
+{
+	return atomic_read(&cl->remaining) & CLOSURE_REMAINING_MASK;
+}
+
 /**
  * closure_sync - sleep until a closure a closure has nothing left to wait on
  *
@@ -180,7 +185,7 @@ void __closure_sync(struct closure *cl);
  */
 static inline void closure_sync(struct closure *cl)
 {
-	if ((atomic_read(&cl->remaining) & CLOSURE_REMAINING_MASK) != 1)
+	if (closure_nr_remaining(cl) != 1)
 		__closure_sync(cl);
 }