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: Li Dongyang <lidongyang@novell.com>
Acked-by: Mark Fasheh <mfasheh@suse.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>

fs/ocfs2/file.c

@@ -1982,18 +1982,18 @@ 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)
-			goto out_dio;
+	ret = generic_segment_checks(iov, &nr_segs, &ocount,
+				     VERIFY_READ);
+	if (ret)
+		goto out_dio;
 
-		count = ocount;
-		ret = generic_write_checks(file, ppos, &count,
-					   S_ISBLK(inode->i_mode));
-		if (ret)
-			goto out_dio;
+	count = ocount;
+	ret = generic_write_checks(file, ppos, &count,
+				   S_ISBLK(inode->i_mode));
+	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: