linux-kernel - Re: lockdep WARNING in get_online

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Message-ID: <20160405111820.GK3448@twins.programming.kicks-ass.net>
Date:	Tue, 5 Apr 2016 13:18:20 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Dmitry Vyukov <dvyukov@...gle.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"x86@...nel.org" <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	syzkaller <syzkaller@...glegroups.com>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>
Subject: Re: lockdep WARNING in get_online_cpus

On Tue, Apr 05, 2016 at 11:44:13AM +0200, Dmitry Vyukov wrote:
> On Tue, Apr 5, 2016 at 11:41 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> > On Mon, Apr 04, 2016 at 11:50:07AM +0200, Dmitry Vyukov wrote:
> >> Yes, I am able to reproduce it by running:
> >>
> >> # ./syz-execprog  -cover=0 -repeat=0 -procs=20 -nobody=0
> >> crash-qemu-26-1459761514194788294
> >>
> >> crash-qemu-26-1459761514194788294 being:
> >> https://gist.githubusercontent.com/dvyukov/bce719c2b7dede54f96d8bbb7c78714f/raw/08a7a237986f0e3bccc7c0e800a3bdaa32e1fc0b/gistfile1.txt
> >
> >
> > root@...-ep:~/gopath/src/github.com/google/syzkaller# ./bin/syz-execprog -cover=0 -repeat=0 -procs=20 -nobody=0 gistfile1.txt
> > 2016/04/05 11:39:37 parsed 391 programs
> > 2016/04/05 11:39:37 executed 0 programs
> > result: failed=false hanged=false err=failed to start executor binary: fork/exec /root/gopath/src/github.com/google/syzkaller: permission denied
> >
> > result: failed=false hanged=false err=failed to start executor binary: fork/exec /root/gopath/src/github.com/google/syzkaller: permission denied
> >
> > result: failed=false hanged=false err=failed to start executor binary: fork/exec /root/gopath/src/github.com/google/syzkaller: permission denied
> >
> > (which goes on ad inf.)
> >
> > Clearly I'm not doing it right.. help?
> 
> The latest version of syz-execproc uses ./syz-executor by default. If
> you don't have ./syz-executor, add -executor=/path/to/syz-executor.

I still have the version you helped make work; I saw that the config
file format had changed since so I've not updated because I didn't want
borkage.

In any case, that did indeed work. But it doesn't trigger the collision
for me :/

I'm running a fairly bloated (distro derived) .config with various debug
options (including lockdep and lockdep_debug) enabled.

Should I maybe do a 'normal' fuzz run to see if that will trigger it? I
need a config for that though, as I only have the perf specific one.
Also, how likely is running this thing as root on bare metal going to
wreck things?