atomics/generic: Define atomic64_fetch_add_unless()

As a step towards unifying the atomic/atomic64/atomic_long APIs, this
patch converts the generic implementation of atomic64_add_unless() into
a generic implementation of atomic64_fetch_add_unless().

A wrapper in <linux/atomic.h> will build atomic_add_unless() atop of
this, provided it is given a preprocessor definition.

No functional change is intended as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Will Deacon <will.deacon@arm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/lkml/20180621121321.4761-9-mark.rutland@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

Author: mrutland-arm

include/asm-generic/atomic64.h

@@ -53,7 +53,8 @@ ATOMIC64_OPS(xor)
 extern long long atomic64_dec_if_positive(atomic64_t *v);
 extern long long atomic64_cmpxchg(atomic64_t *v, long long o, long long n);
 extern long long atomic64_xchg(atomic64_t *v, long long new);
-extern bool	 atomic64_add_unless(atomic64_t *v, long long a, long long u);
+extern long long atomic64_fetch_add_unless(atomic64_t *v, long long a, long long u);
+#define atomic64_fetch_add_unless atomic64_fetch_add_unless
 
 #define atomic64_add_negative(a, v)	(atomic64_add_return((a), (v)) < 0)
 #define atomic64_inc(v)			atomic64_add(1LL, (v))

lib/atomic64.c

@@ -178,18 +178,18 @@ long long atomic64_xchg(atomic64_t *v, long long new)
 }
 EXPORT_SYMBOL(atomic64_xchg);
 
-bool atomic64_add_unless(atomic64_t *v, long long a, long long u)
+long long atomic64_fetch_add_unless(atomic64_t *v, long long a, long long u)
 {
 	unsigned long flags;
 	raw_spinlock_t *lock = lock_addr(v);
-	bool ret = false;
+	long long val;
 
 	raw_spin_lock_irqsave(lock, flags);
-	if (v->counter != u) {
+	val = v->counter;
+	if (val != u)
 		v->counter += a;
-		ret = true;
-	}
 	raw_spin_unlock_irqrestore(lock, flags);
-	return ret;
+
+	return val;
 }
-EXPORT_SYMBOL(atomic64_add_unless);
+EXPORT_SYMBOL(atomic64_fetch_add_unless);