ocfs2: Avoid direct write if we fall back to buffered I/O

when we fall back to buffered write from direct write, we call
__generic_file_aio_write() but that will end up doing direct write
even we are only prepared to do buffered write because the file
has the O_DIRECT flag set. This is a fix for
https://bugzilla.novell.com/show_bug.cgi?id=591039
revised with Joel's comments.
Signed-off-by: NLi Dongyang <lidongyang@novell.com>
Acked-by: NMark Fasheh <mfasheh@suse.com>
Signed-off-by: NJoel Becker <joel.becker@oracle.com>

fs/ocfs2/file.c

@@ -1982,7 +1982,6 @@ static ssize_t ocfs2_file_aio_write(struct kiocb *iocb,
 	/* communicate with ocfs2_dio_end_io */
 	ocfs2_iocb_set_rw_locked(iocb, rw_level);
 
-	if (direct_io) {
 	ret = generic_segment_checks(iov, &nr_segs, &ocount,
 				     VERIFY_READ);
 	if (ret)
@@ -1994,6 +1993,7 @@ static ssize_t ocfs2_file_aio_write(struct kiocb *iocb,
 	if (ret)
 		goto out_dio;
 
+	if (direct_io) {
 		written = generic_file_direct_write(iocb, iov, &nr_segs, *ppos,
 						    ppos, count, ocount);
 		if (written < 0) {
@@ -2008,7 +2008,10 @@ static ssize_t ocfs2_file_aio_write(struct kiocb *iocb,
 			goto out_dio;
 		}
 	} else {
-		written = __generic_file_aio_write(iocb, iov, nr_segs, ppos);
+		current->backing_dev_info = file->f_mapping->backing_dev_info;
+		written = generic_file_buffered_write(iocb, iov, nr_segs, *ppos,
+						      ppos, count, 0);
+		current->backing_dev_info = NULL;
 	}
 
 out_dio: