f2fs: check end_io for metapages before making next checkpoint blocks

This patch avoids to produce new checkpoint blocks before the previous meta
pages were written completely.

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
index c5a38e3..ff53405 100644
--- a/fs/f2fs/checkpoint.c
+++ b/fs/f2fs/checkpoint.c
@@ -1000,6 +1000,11 @@
 
 	start_blk = __start_cp_addr(sbi);
 
+	/* need to wait for end_io results */
+	wait_on_all_pages_writeback(sbi);
+	if (unlikely(f2fs_cp_error(sbi)))
+		return;
+
 	/* write out checkpoint buffer at block 0 */
 	update_meta_page(sbi, ckpt, start_blk++);