Btrfs: don't reserve data with extents locked in btrfs_fallocate

btrfs_fallocate tries to allocate space only if ranges in the file don't
already exist.  But the enospc checks it does are not allowed with
extents locked.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

fs/btrfs/file.c

@@ -1603,6 +1603,14 @@ static long btrfs_fallocate(struct file *file, int mode,
 	if (mode & ~FALLOC_FL_KEEP_SIZE)
 		return -EOPNOTSUPP;
 
+	/*
+	 * Make sure we have enough space before we do the
+	 * allocation.
+	 */
+	ret = btrfs_check_data_free_space(inode, len);
+	if (ret)
+		return ret;
+
 	/*
 	 * wait for ordered IO before we have any locks.  We'll loop again
 	 * below with the locks held.
@@ -1666,27 +1674,12 @@ static long btrfs_fallocate(struct file *file, int mode,
 		if (em->block_start == EXTENT_MAP_HOLE ||
 		    (cur_offset >= inode->i_size &&
 		     !test_bit(EXTENT_FLAG_PREALLOC, &em->flags))) {
-
-			/*
-			 * Make sure we have enough space before we do the
-			 * allocation.
-			 */
-			ret = btrfs_check_data_free_space(inode, last_byte -
-							  cur_offset);
-			if (ret) {
-				free_extent_map(em);
-				break;
-			}
-
 			ret = btrfs_prealloc_file_range(inode, mode, cur_offset,
 							last_byte - cur_offset,
 							1 << inode->i_blkbits,
 							offset + len,
 							&alloc_hint);
 
-			/* Let go of our reservation. */
-			btrfs_free_reserved_data_space(inode, last_byte -
-						       cur_offset);
 			if (ret < 0) {
 				free_extent_map(em);
 				break;
@@ -1714,6 +1707,8 @@ static long btrfs_fallocate(struct file *file, int mode,
 			     &cached_state, GFP_NOFS);
 out:
 	mutex_unlock(&inode->i_mutex);
+	/* Let go of our reservation. */
+	btrfs_free_reserved_data_space(inode, len);
 	return ret;
 }