Btrfs: wait ordered range before doing direct io

My recent truncate patch uncovered this bug, but I can reproduce it without the
truncate patch.  If you mount with -o compress-force, do a direct write to some
area, do a buffered write to some other area, and then do a direct read you will
get the wrong data for where you did the buffered write.  This is because the
generic direct io helpers only call filemap_write_and_wait once, and for
compression we need it twice.  So to be safe add the btrfs_wait_ordered_range to
the start of the direct io function to make sure any compressed writes have
truly been written.  This patch makes xfstests 130 pass when you mount with -o
compress-force=lzo.  Thanks,
Signed-off-by: NJosef Bacik <jbacik@fusionio.com>

fs/btrfs/inode.c

@@ -7270,8 +7270,16 @@ static ssize_t btrfs_direct_IO(int rw, struct kiocb *iocb,
 	atomic_inc(&inode->i_dio_count);
 	smp_mb__after_atomic_inc();
 
+	/*
+	 * The generic stuff only does filemap_write_and_wait_range, which isn't
+	 * enough if we've written compressed pages to this area, so we need to
+	 * call btrfs_wait_ordered_range to make absolutely sure that any
+	 * outstanding dirty pages are on disk.
+	 */
+	count = iov_length(iov, nr_segs);
+	btrfs_wait_ordered_range(inode, offset, count);
+
 	if (rw & WRITE) {
-		count = iov_length(iov, nr_segs);
 		/*
 		 * If the write DIO is beyond the EOF, we need update
 		 * the isize, but it is protected by i_mutex. So we can