f2fs: fix handling errors got by f2fs_write_inode

Ruslan reported that f2fs hangs with an infinite loop in f2fs_sync_file():

	while (sync_node_pages(sbi, inode->i_ino, &wbc) == 0)
		f2fs_write_inode(inode, NULL);

The reason was revealed that the cold flag is not set even thought this inode is
a normal file. Therefore, sync_node_pages() skips to write node blocks since it
only writes cold node blocks.

The cold flag is stored to the node_footer in node block, and whenever a new
node page is allocated, it is set according to its file type, file or directory.

But, after sudden-power-off, when recovering the inode page, f2fs doesn't recover
its cold flag.

So, let's assign the cold flag in more right places.

One more thing:
If f2fs_write_inode() returns an error due to whatever situations, there would
be no dirty node pages so that sync_node_pages() returns zero.
(i.e., zero means nothing was written.)

Reported-by: Ruslan N. Marchenko <me@ruff.mobi>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

fs/f2fs/node.c

@@ -834,11 +834,11 @@ struct page *new_node_page(struct dnode_of_data *dn, unsigned int ofs)
 		goto fail;
 	}
 	set_node_addr(sbi, &new_ni, NEW_ADDR);
+	set_cold_node(dn->inode, page);
 
 	dn->node_page = page;
 	sync_inode_page(dn);
 	set_page_dirty(page);
-	set_cold_node(dn->inode, page);
 	if (ofs == 0)
 		inc_valid_inode_count(sbi);