btrfs: use btrfs_try_lock_balance in btrfs_ioctl_balance

This eliminates 2 labels and makes the code generally more streamlined.
Also rename the 'out_bargs' label to 'out_unlock' since bargs is going
to be freed under the 'out' label. This also fixes a memory leak since
bargs wasn't correctly freed in one of the condition which are now moved
in btrfs_try_lock_balance.

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

@@ -4427,7 +4427,7 @@ static long btrfs_ioctl_balance(struct file *file, void __user *arg)
 	struct btrfs_fs_info *fs_info = root->fs_info;
 	struct btrfs_ioctl_balance_args *bargs;
 	struct btrfs_balance_control *bctl;
-	bool need_unlock; /* for mut. excl. ops lock */
+	bool need_unlock = true;
 	int ret;
 
 	if (!capable(CAP_SYS_ADMIN))
@@ -4444,53 +4444,12 @@ static long btrfs_ioctl_balance(struct file *file, void __user *arg)
 		goto out;
 	}
 
-again:
-	if (btrfs_exclop_start(fs_info, BTRFS_EXCLOP_BALANCE)) {
-		mutex_lock(&fs_info->balance_mutex);
-		need_unlock = true;
-		goto locked;
-	}
-
-	/*
-	 * mut. excl. ops lock is locked.  Three possibilities:
-	 *   (1) some other op is running
-	 *   (2) balance is running
-	 *   (3) balance is paused -- special case (think resume)
-	 */
-	mutex_lock(&fs_info->balance_mutex);
-	if (fs_info->balance_ctl) {
-		/* this is either (2) or (3) */
-		if (!test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags)) {
-			mutex_unlock(&fs_info->balance_mutex);
-			/*
-			 * Lock released to allow other waiters to continue,
-			 * we'll reexamine the status again.
-			 */
-			mutex_lock(&fs_info->balance_mutex);
-
-			if (fs_info->balance_ctl &&
-			    !test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags)) {
-				/* this is (3) */
-				need_unlock = false;
-				goto locked;
-			}
-
-			mutex_unlock(&fs_info->balance_mutex);
-			goto again;
-		} else {
-			/* this is (2) */
-			mutex_unlock(&fs_info->balance_mutex);
-			ret = -EINPROGRESS;
-			goto out;
-		}
-	} else {
-		/* this is (1) */
-		mutex_unlock(&fs_info->balance_mutex);
-		ret = BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
+	ret = btrfs_try_lock_balance(fs_info, &need_unlock);
+	if (ret)
 		goto out;
-	}
 
-locked:
+	lockdep_assert_held(&fs_info->balance_mutex);
+
 	if (bargs->flags & BTRFS_BALANCE_RESUME) {
 		if (!fs_info->balance_ctl) {
 			ret = -ENOTCONN;