ppc64: merge in ppc32 changes to atomic_dec_and_lock

arch/ppc64/lib/dec_and_lock.c

@@ -7,32 +7,49 @@
  * 2 of the License, or (at your option) any later version.
  */
 
+#include <linux/module.h>
 #include <linux/spinlock.h>
-#include <asm/system.h>
 #include <asm/atomic.h>
+#include <asm/system.h>
 
+/*
+ * This is an implementation of the notion of "decrement a
+ * reference count, and return locked if it decremented to zero".
+ *
+ * This implementation can be used on any architecture that
+ * has a cmpxchg, and where atomic->value is an int holding
+ * the value of the atomic (i.e. the high bits aren't used
+ * for a lock or anything like that).
+ *
+ * N.B. ATOMIC_DEC_AND_LOCK gets defined in include/linux/spinlock.h
+ * if spinlocks are empty and thus atomic_dec_and_lock is defined
+ * to be atomic_dec_and_test - in that case we don't need it
+ * defined here as well.
+ */
+
+#ifndef ATOMIC_DEC_AND_LOCK
 int atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
 {
 	int counter;
 	int newcount;
 
-repeat:
-	counter = atomic_read(atomic);
-	newcount = counter-1;
-
-	if (!newcount)
-		goto slow_path;
+	for (;;) {
+		counter = atomic_read(atomic);
+		newcount = counter - 1;
+		if (!newcount)
+			break;		/* do it the slow way */
 
-	newcount = cmpxchg(&atomic->counter, counter, newcount);
+		newcount = cmpxchg(&atomic->counter, counter, newcount);
+		if (newcount == counter)
+			return 0;
+	}
 
-	if (newcount != counter)
-		goto repeat;
-	return 0;
-
-slow_path:
 	spin_lock(lock);
 	if (atomic_dec_and_test(atomic))
 		return 1;
 	spin_unlock(lock);
 	return 0;
 }
+
+EXPORT_SYMBOL(atomic_dec_and_lock);
+#endif /* ATOMIC_DEC_AND_LOCK */