ext4: fix ext4_writepage() to achieve data=ordered guarantees

		len = PAGE_CACHE_SIZE;

	page_bufs = page_buffers(page);

	/*

	 * We cannot do block allocation or other extent handling in this

	 * function. If there are buffers needing that, we have to redirty

	 * the page. But we may reach here when we do a journal commit via

	 * journal_submit_inode_data_buffers() and in that case we must write

	 * allocated buffers to achieve data=ordered mode guarantees.

	 */

	if (ext4_walk_page_buffers(NULL, page_bufs, 0, len, NULL,

				   ext4_bh_delay_or_unwritten)) {

		redirty_page_for_writepage(wbc, page);

		if (current->flags & PF_MEMALLOC) {

			/*

		 * We don't want to do block allocation, so redirty

		 * the page and return.  We may reach here when we do

		 * a journal commit via journal_submit_inode_data_buffers.

		 * We can also reach here via shrink_page_list but it

		 * should never be for direct reclaim so warn if that

		 * happens

			 * For memory cleaning there's no point in writing only

			 * some buffers. So just bail out. Warn if we came here

			 * from direct reclaim.

			 */

		WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD)) ==

								PF_MEMALLOC);

		redirty_page_for_writepage(wbc, page);

			WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD))

							== PF_MEMALLOC);

			unlock_page(page);

			return 0;

		}

	}

	if (PageChecked(page) && ext4_should_journal_data(inode))

		/*