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 S1754375AbbLJRDO (ORCPT <rfc822;w@1wt.eu>);
	Thu, 10 Dec 2015 12:03:14 -0500
Received: from mail-pf0-f181.google.com ([209.85.192.181]:36252 "EHLO
	mail-pf0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1753887AbbLJRDK (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Thu, 10 Dec 2015 12:03:10 -0500
Date: Thu, 10 Dec 2015 09:03:06 -0800
From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Dmitry Vyukov <dvyukov@google.com>, syzkaller <syzkaller@googlegroups.com>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Kostya Serebryany <kcc@google.com>,
        Alexander Potapenko <glider@google.com>,
        Eric Dumazet <edumazet@google.com>,
        Sasha Levin <sasha.levin@oracle.com>
Subject: Re: use-after-free in __perf_install_in_context
Message-ID: <20151210170305.GA28459@ast-mbp.thefacebook.com>
References: <20151208032405.GA47397@ast-mbp.thefacebook.com>
 <CACT4Y+ZsKVN+FXjyRNYgtWxMjjYfB9uz8f0QAW7iGjLE5GCQBA@mail.gmail.com>
 <20151208175433.GA75053@ast-mbp.thefacebook.com>
 <CACT4Y+Y_w4oteNLKGE4gVqOpoyrmm+3VQDemGGScbepnXhL4VA@mail.gmail.com>
 <20151208180528.GA77166@ast-mbp.thefacebook.com>
 <CACT4Y+Y-wBH+xfei_q-6FcEoShM8sX4eX3bQyfEppWy522RiYw@mail.gmail.com>
 <20151208195623.GA92501@ast-mbp.thefacebook.com>
 <CACT4Y+bKU96_CPqC6CxJ-M7rnbiBa4sY2BesDMTXf+uLTjjv=Q@mail.gmail.com>
 <20151210035434.GA11217@ast-mbp.thefacebook.com>
 <20151210090251.GV6356@twins.programming.kicks-ass.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20151210090251.GV6356@twins.programming.kicks-ass.net>
User-Agent: Mutt/1.5.24 (2015-08-30)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Thu, Dec 10, 2015 at 10:02:51AM +0100, Peter Zijlstra wrote:
> On Wed, Dec 09, 2015 at 07:54:35PM -0800, Alexei Starovoitov wrote:
> > Freeing memory is a requirement regardless.
> > Even when kernel running with kasan, there must be a way to stop
> > stack collection and free that memory.
> > You cannot treat kernel as your test program or 'device under test'.
> 
> Relax, that is exactly what lockdep does. It cannot dynamically allocate
> things because allocators use lock etc..
> 
> Its fine to build up state for debug bits, esp. if its bounded, like the
> number of unique callchains.

except the code in question is doing unbounded alloc_pages()