f2fs: avoid inifinite loop to wait for flushing node pages at cp_error

Shutdown test is somtimes hung, since it keeps trying to flush dirty node pages
in an inifinite loop. Let's drop dirty pages at umount in that case.
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/node.c

@@ -1520,8 +1520,15 @@ static int __write_node_page(struct page *page, bool atomic, bool *submitted,
 
 	trace_f2fs_writepage(page, NODE);
 
-	if (unlikely(f2fs_cp_error(sbi)))
+	if (unlikely(f2fs_cp_error(sbi))) {
+		if (is_sbi_flag_set(sbi, SBI_IS_CLOSE)) {
+			ClearPageUptodate(page);
+			dec_page_count(sbi, F2FS_DIRTY_NODES);
+			unlock_page(page);
+			return 0;
+		}
 		goto redirty_out;
+	}
 
 	if (unlikely(is_sbi_flag_set(sbi, SBI_POR_DOING)))
 		goto redirty_out;