nfsd: make sure data is on disk before calling ->fsync

nfsd is not using vfs_fsync, so I missed it when changing the calling
convention during the 2.6.32 window.  This patch fixes it to not only
start the data writeout, but also wait for it to complete before calling
into ->fsync.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Cc: stable@kernel.org
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

fs/nfsd/vfs.c

@@ -782,12 +782,9 @@ static inline int nfsd_dosync(struct file *filp, struct dentry *dp,
 	int (*fsync) (struct file *, struct dentry *, int);
 	int err;
 
-	err = filemap_fdatawrite(inode->i_mapping);
+	err = filemap_write_and_wait(inode->i_mapping);
 	if (err == 0 && fop && (fsync = fop->fsync))
 		err = fsync(filp, dp, 0);
-	if (err == 0)
-		err = filemap_fdatawait(inode->i_mapping);
-
 	return err;
 }