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 S934752AbcIOMl5 (ORCPT <rfc822;w@1wt.eu>);
        Thu, 15 Sep 2016 08:41:57 -0400
Received: from mail-it0-f42.google.com ([209.85.214.42]:37972 "EHLO
        mail-it0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1763607AbcIOMlz (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Thu, 15 Sep 2016 08:41:55 -0400
From: Vince Weaver <vincent.weaver@maine.edu>
X-Google-Original-From: Vince Weaver <vince@maine.edu>
Date: Thu, 15 Sep 2016 08:41:52 -0400 (EDT)
X-X-Sender: vince@macbook-air
To: Peter Zijlstra <peterz@infradead.org>
cc: linux-kernel@vger.kernel.org,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Stephane Eranian <eranian@google.com>, Ingo Molnar <mingo@kernel.org>
Subject: Re: perf: perf_fuzzer lockup in perf_cgroup_attach
In-Reply-To: <20160915071500.GM5008@twins.programming.kicks-ass.net>
Message-ID: <alpine.DEB.2.20.1609150839130.13216@macbook-air>
References: <alpine.DEB.2.20.1609142224480.12612@macbook-air> <20160915071500.GM5008@twins.programming.kicks-ass.net>
User-Agent: Alpine 2.20 (DEB 67 2015-01-07)
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Thu, 15 Sep 2016, Peter Zijlstra wrote:

> On Wed, Sep 14, 2016 at 10:43:29PM -0400, Vince Weaver wrote:
> > 
> > so the skylake that was fuzzing finally is mostly locked up.
> > 
> > Really hard to tell what's going, especially as KASLR made looking up the 
> > addresses a big pain.
> > 
> > The best I can tell things are getting wedged somehow in 
> > perf_cgroup_switch() while interrupts are disabled.  Interrupts are never 
> > getting re-enabled, causing the RCU and NMI watchdogs to trigger (and more 
> > alarming things like the SATA bus resetting).
> 
> How do you go about using cgroups? Do you set them up yourself, does the
> fuzzer do so?

that's an interesting thing, I don't think the fuzzer actually sets up any 
cgroups.  It will try creating events with PERF_FLAG_PID_CGROUP but it 
will just use a random number as the cgroup fd.  

I know at one time I meant to do more interesting things with cgroups
but if I recall it wasn't really possible without running as root and I 
usually don't fuzz as root.

Vince