mm/swap_slots.c: simplify enable_swap_slots_cache()

Whether swap_slot_cache_initialized is true or false,
__reenable_swap_slots_cache() is always called.  To make this meaning
clear, leave only one call to __reenable_swap_slots_cache().  This also
make it clearer what extra needs be done when swap_slot_cache_initialized
is false.

No functional change.
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Tim Chen <tim.c.chen@linux.intel.com>
Link: http://lkml.kernel.org/r/20200430061143.450-3-thunder.leizhen@huawei.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/swap_slots.c

@@ -240,21 +240,19 @@ static int free_slot_cache(unsigned int cpu)
 
 int enable_swap_slots_cache(void)
 {
-	int ret = 0;
-
 	mutex_lock(&swap_slots_cache_enable_mutex);
-	if (swap_slot_cache_initialized) {
-		__reenable_swap_slots_cache();
-		goto out_unlock;
-	}
+	if (!swap_slot_cache_initialized) {
+		int ret;
 
-	ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "swap_slots_cache",
-				alloc_swap_slot_cache, free_slot_cache);
-	if (WARN_ONCE(ret < 0, "Cache allocation failed (%s), operating "
-			       "without swap slots cache.\n", __func__))
-		goto out_unlock;
+		ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "swap_slots_cache",
+					alloc_swap_slot_cache, free_slot_cache);
+		if (WARN_ONCE(ret < 0, "Cache allocation failed (%s), operating "
+				       "without swap slots cache.\n", __func__))
+			goto out_unlock;
+
+		swap_slot_cache_initialized = true;
+	}
 
-	swap_slot_cache_initialized = true;
 	__reenable_swap_slots_cache();
 out_unlock:
 	mutex_unlock(&swap_slots_cache_enable_mutex);