Btrfs: apply updated fallocate i_size fix

commit 23b5c509 upstream.

This version of the i_size fix for fallocate makes sure we only update
the i_size when the current fallocate is really operating outside of
i_size.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
Acked-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

fs/btrfs/inode.c

@@ -5798,7 +5798,9 @@ static int prealloc_file_range(struct inode *inode, u64 start, u64 end,
 		inode->i_ctime = CURRENT_TIME;
 		BTRFS_I(inode)->flags |= BTRFS_INODE_PREALLOC;
 		if (!(mode & FALLOC_FL_KEEP_SIZE) &&
-		    cur_offset > inode->i_size) {
+			(actual_len > inode->i_size) &&
+			(cur_offset > inode->i_size)) {
+
 			if (cur_offset > actual_len)
 				i_size  = actual_len;
 			else