From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1751975AbbI2W5O (ORCPT <rfc822;w@1wt.eu>);
	Tue, 29 Sep 2015 18:57:14 -0400
Received: from mail.linuxfoundation.org ([140.211.169.12]:37709 "EHLO
	mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1750810AbbI2W5M (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Tue, 29 Sep 2015 18:57:12 -0400
Date: Tue, 29 Sep 2015 15:57:11 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Vladimir Davydov <vdavydov@parallels.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>, Michal Hocko <mhocko@kernel.org>,
        Tejun Heo <tj@kernel.org>, <linux-mm@kvack.org>,
        <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/5] fs: charge pipe buffers to memcg
Message-Id: <20150929155711.3b139dab622848a14af64ca4@linux-foundation.org>
In-Reply-To: <94f055dc719129a26149b0f8b22af7c61a3fb4e6.1443262808.git.vdavydov@parallels.com>
References: <cover.1443262808.git.vdavydov@parallels.com>
	<94f055dc719129a26149b0f8b22af7c61a3fb4e6.1443262808.git.vdavydov@parallels.com>
X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu)
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Sat, 26 Sep 2015 13:45:54 +0300 Vladimir Davydov <vdavydov@parallels.com> wrote:

> Pipe buffers can be generated unrestrictedly by an unprivileged
> userspace process, so they shouldn't go unaccounted.
> 
> ...
>
> --- a/fs/pipe.c
> +++ b/fs/pipe.c
> @@ -400,7 +400,7 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
>  			int copied;
>  
>  			if (!page) {
> -				page = alloc_page(GFP_HIGHUSER);
> +				page = alloc_kmem_pages(GFP_HIGHUSER, 0);
>  				if (unlikely(!page)) {
>  					ret = ret ? : -ENOMEM;
>  					break;

This seems broken.  We have a page buffer page which has a weird
->mapcount.  Now it gets stolen (generic_pipe_buf_steal()) and spliced
into pagecache.  Then the page gets mmapped and MM starts playing with
its ->_mapcount?