linux-kernel - Re: lockdep WARNING in get_online

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Message-ID: <CACT4Y+Y9juC5=d_uujCpO8_UASb2Vam+CjposuohX5TiK6v0sQ@mail.gmail.com>
Date:	Tue, 5 Apr 2016 13:23:41 +0200
From:	Dmitry Vyukov <dvyukov@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
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 5, 2016 at 1:18 PM, Peter Zijlstra <peterz@...radead.org> 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.


Try to run it for several minutes, then reboot machine and try again.
It seems to be somewhat non-deterministic (maybe depends on order
chains are added to hashtable).


> 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?

We are running syzkaller on an android device for a months, no issues
observed (we don't even reimage it).

My config just includes:

        "disable_syscalls": [
                "syz_open_dev$kvm"
        ],

and no "enable_syscalls". I don't know what would be a more
specialized config for this issue.