btrfs: simplify code flow in btrfs_ioctl_balance

Move code in btrfs_ioctl_balance to simplify its flow. This is
possible thanks to the removal of balance v1 ioctl and ensuring 'arg'
argument is always present. First move the code duplicating the
userspace arg to the kernel 'barg'. This makes the out_unlock label
redundant.  Secondly, check the validity of bargs::flags before copying
to the dynamically allocated 'bctl'. This removes the need for the
out_bctl label.
Reviewed-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ioctl.c

@@ -4353,6 +4353,13 @@ static long btrfs_ioctl_balance(struct file *file, void __user *arg)
 	if (ret)
 		return ret;
 
+	bargs = memdup_user(arg, sizeof(*bargs));
+	if (IS_ERR(bargs)) {
+		ret = PTR_ERR(bargs);
+		bargs = NULL;
+		goto out;
+	}
+
 again:
 	if (btrfs_exclop_start(fs_info, BTRFS_EXCLOP_BALANCE)) {
 		mutex_lock(&fs_info->balance_mutex);
@@ -4400,17 +4407,10 @@ static long btrfs_ioctl_balance(struct file *file, void __user *arg)
 	}
 
 locked:
-
-	bargs = memdup_user(arg, sizeof(*bargs));
-	if (IS_ERR(bargs)) {
-		ret = PTR_ERR(bargs);
-		goto out_unlock;
-	}
-
 	if (bargs->flags & BTRFS_BALANCE_RESUME) {
 		if (!fs_info->balance_ctl) {
 			ret = -ENOTCONN;
-			goto out_bargs;
+			goto out_unlock;
 		}
 
 		bctl = fs_info->balance_ctl;
@@ -4422,15 +4422,20 @@ static long btrfs_ioctl_balance(struct file *file, void __user *arg)
 		goto do_balance;
 	}
 
+	if (bargs->flags & ~(BTRFS_BALANCE_ARGS_MASK | BTRFS_BALANCE_TYPE_MASK)) {
+		ret = -EINVAL;
+		goto out_unlock;
+	}
+
 	if (fs_info->balance_ctl) {
 		ret = -EINPROGRESS;
-		goto out_bargs;
+		goto out_unlock;
 	}
 
 	bctl = kzalloc(sizeof(*bctl), GFP_KERNEL);
 	if (!bctl) {
 		ret = -ENOMEM;
-		goto out_bargs;
+		goto out_unlock;
 	}
 
 	memcpy(&bctl->data, &bargs->data, sizeof(bctl->data));
@@ -4438,12 +4443,6 @@ static long btrfs_ioctl_balance(struct file *file, void __user *arg)
 	memcpy(&bctl->sys, &bargs->sys, sizeof(bctl->sys));
 
 	bctl->flags = bargs->flags;
-
-	if (bctl->flags & ~(BTRFS_BALANCE_ARGS_MASK | BTRFS_BALANCE_TYPE_MASK)) {
-		ret = -EINVAL;
-		goto out_bctl;
-	}
-
 do_balance:
 	/*
 	 * Ownership of bctl and exclusive operation goes to btrfs_balance.
@@ -4461,16 +4460,14 @@ static long btrfs_ioctl_balance(struct file *file, void __user *arg)
 			ret = -EFAULT;
 	}
 
-out_bctl:
 	kfree(bctl);
-out_bargs:
-	kfree(bargs);
 out_unlock:
 	mutex_unlock(&fs_info->balance_mutex);
 	if (need_unlock)
 		btrfs_exclop_finish(fs_info);
 out:
 	mnt_drop_write_file(file);
+	kfree(bargs);
 	return ret;
 }