md: refactor mddev_find_or_alloc

Allocate the new mddev first speculatively, which greatly simplifies
the code flow.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NSong Liu <song@kernel.org>

drivers/md/md.c

@@ -784,57 +784,45 @@ static struct mddev *mddev_find(dev_t unit)
 
 static struct mddev *mddev_find_or_alloc(dev_t unit)
 {
-	struct mddev *mddev, *new = NULL;
+	struct mddev *mddev = NULL, *new;
 
 	if (unit && MAJOR(unit) != MD_MAJOR)
-		unit &= ~((1<<MdpMinorShift)-1);
+		unit &= ~((1 << MdpMinorShift) - 1);
 
- retry:
-	spin_lock(&all_mddevs_lock);
+	new = kzalloc(sizeof(*new), GFP_KERNEL);
+	if (!new)
+		return NULL;
+	mddev_init(new);
 
+	spin_lock(&all_mddevs_lock);
 	if (unit) {
 		mddev = mddev_find_locked(unit);
 		if (mddev) {
 			mddev_get(mddev);
-			spin_unlock(&all_mddevs_lock);
-			kfree(new);
-			return mddev;
+			goto out_free_new;
 		}
 
-		if (new) {
-			list_add(&new->all_mddevs, &all_mddevs);
-			spin_unlock(&all_mddevs_lock);
-			new->hold_active = UNTIL_IOCTL;
-			return new;
-		}
-	} else if (new) {
+		new->unit = unit;
+		if (MAJOR(unit) == MD_MAJOR)
+			new->md_minor = MINOR(unit);
+		else
+			new->md_minor = MINOR(unit) >> MdpMinorShift;
+		new->hold_active = UNTIL_IOCTL;
+	} else {
 		new->unit = mddev_alloc_unit();
-		if (!new->unit) {
-			spin_unlock(&all_mddevs_lock);
-			kfree(new);
-			return NULL;
-		}
+		if (!new->unit)
+			goto out_free_new;
 		new->md_minor = MINOR(new->unit);
 		new->hold_active = UNTIL_STOP;
-		list_add(&new->all_mddevs, &all_mddevs);
-		spin_unlock(&all_mddevs_lock);
-		return new;
 	}
-	spin_unlock(&all_mddevs_lock);
-
-	new = kzalloc(sizeof(*new), GFP_KERNEL);
-	if (!new)
-		return NULL;
 
-	new->unit = unit;
-	if (MAJOR(unit) == MD_MAJOR)
-		new->md_minor = MINOR(unit);
-	else
-		new->md_minor = MINOR(unit) >> MdpMinorShift;
-
-	mddev_init(new);
-
-	goto retry;
+	list_add(&new->all_mddevs, &all_mddevs);
+	spin_unlock(&all_mddevs_lock);
+	return new;
+out_free_new:
+	spin_unlock(&all_mddevs_lock);
+	kfree(new);
+	return mddev;
 }
 
 static struct attribute_group md_redundancy_group;