f2fs: wait on page's writeback in writepages path

Likewise f2fs_write_cache_pages, let's do for node and meta pages too.
Especially, for node blocks, we should do this before marking its fsync
and dentry flags.
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/checkpoint.c

@@ -232,7 +232,6 @@ static int f2fs_write_meta_page(struct page *page,
 	if (unlikely(f2fs_cp_error(sbi)))
 		goto redirty_out;
 
-	f2fs_wait_on_page_writeback(page, META, true);
 	write_meta_page(sbi, page);
 	dec_page_count(sbi, F2FS_DIRTY_META);
 	unlock_page(page);
@@ -315,6 +314,9 @@ long sync_meta_pages(struct f2fs_sb_info *sbi, enum page_type type,
 				goto continue_unlock;
 			}
 
+			f2fs_wait_on_page_writeback(page, META, true);
+
+			BUG_ON(PageWriteback(page));
 			if (!clear_page_dirty_for_io(page))
 				goto continue_unlock;
 

fs/f2fs/node.c

@@ -1297,6 +1297,9 @@ int sync_node_pages(struct f2fs_sb_info *sbi, nid_t ino,
 				continue;
 			}
 
+			f2fs_wait_on_page_writeback(page, NODE, true);
+
+			BUG_ON(PageWriteback(page));
 			if (!clear_page_dirty_for_io(page))
 				goto continue_unlock;
 
@@ -1402,8 +1405,6 @@ static int f2fs_write_node_page(struct page *page,
 	if (unlikely(f2fs_cp_error(sbi)))
 		goto redirty_out;
 
-	f2fs_wait_on_page_writeback(page, NODE, true);
-
 	/* get old block addr of this node page */
 	nid = nid_of_node(page);
 	f2fs_bug_on(sbi, page->index != nid);