lightnvm: pblk: avoid ref warning on cache creation

The current kref implementation around pblk global caches triggers a
false positive on refcount_inc_checked() (when called) as the kref is
initialized to 0. Instead of usint kref_inc() on a 0 reference, which is
in principle correct, use kref_init() to avoid the check. This is also
more explicit about what actually happens on cache creation.

In the process, do a small refactoring to use kref helpers.

Fixes: 1864de94 "lightnvm: pblk: stop recreating global caches"
Signed-off-by: Javier González <javier@cnexlabs.com>
Reviewed-by: Hans Holmberg <hans.holmberg@cnexlabs.com>
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/lightnvm/pblk-init.c

@@ -347,23 +347,19 @@ static int pblk_create_global_caches(void)
 
 static int pblk_get_global_caches(void)
 {
-	int ret;
+	int ret = 0;
 
 	mutex_lock(&pblk_caches.mutex);
 
-	if (kref_read(&pblk_caches.kref) > 0) {
-		kref_get(&pblk_caches.kref);
-		mutex_unlock(&pblk_caches.mutex);
-		return 0;
-	}
+	if (kref_get_unless_zero(&pblk_caches.kref))
+		goto out;
 
 	ret = pblk_create_global_caches();
-
 	if (!ret)
-		kref_get(&pblk_caches.kref);
+		kref_init(&pblk_caches.kref);
 
+out:
 	mutex_unlock(&pblk_caches.mutex);
-
 	return ret;
 }