linux-kernel - Re: perf: perf_fuzzer quickly locks up on 4.15-rc7

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Message-ID: <20180111153845.GD6176@hirez.programming.kicks-ass.net>
Date:   Thu, 11 Jan 2018 16:38:45 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vince Weaver <vincent.weaver@...ne.edu>
Cc:     Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: perf: perf_fuzzer quickly locks up on 4.15-rc7

On Thu, Jan 11, 2018 at 10:26:14AM -0500, Vince Weaver wrote:
> On Thu, 11 Jan 2018, Peter Zijlstra wrote:
> 
> > I'm seeing things like:
> > 
> > Cannot open /sys/kernel/tracing/kprobe_events
> > 
> > this is likely caused by me not having anything mounted there. Rostedt
> > provided the magic incantation to make that work, I'll go try now.
> 
> The perf_fuzzer krpobe code is possibly really out of date, I haven't 
> really kept up with recent developments and I don't usually fuzz as root.

I was thinking that running as root should be worse than user.. I can
switch to fuzzing as user.. who knows.

> > At least I seem to have cured all lockdep splats.. of course, the moment
> > I hit send on this someone bad is bound to happen.
> 
> Should I be trying any of those patches?

Can't hurt, but I doubt it'll help sone, nothing there is PTI specific.
The force_early_printk stuff helps with printk deadlocks though, hit a
bunch of them earlier today when I build a kernel without them in.

> Currently I can still lock my machines pretty quickly.  I have been doing 
> some more tests.  Machines don't crash if paranoid is "2" but will if 
> paranoid is "1".

OK, I'm going to try fuzzing as a user with paranoid=0, and if that
doesn't help, I'm going to switch to linus' tree with my patches on.