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

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Date:   Wed, 10 Jan 2018 23:25:38 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Vince Weaver <vincent.weaver@...ne.edu>,
        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>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: perf: perf_fuzzer quickly locks up on 4.15-rc7

On Tue, Jan 09, 2018 at 11:07:16AM -0600, Josh Poimboeuf wrote:
> On Tue, Jan 09, 2018 at 05:05:51PM +0100, Peter Zijlstra wrote:
> > On Tue, Jan 09, 2018 at 10:56:52AM -0500, Vince Weaver wrote:
> > > On Tue, 9 Jan 2018, Peter Zijlstra wrote:
> > > 
> > > > So CONFIG_PAGE_TABLE_ISOLATION=y and booting with "pti=off" makes it
> > > > 'work', right?
> > > 
> > > yes.  Previously I was changing CONFIG_PAGE_TABLE_ISOLATION and 
> > > recompiling, but just now I booted with it set to yes and pti=off and the 
> > > fuzzer has been running fine for a half hour (usually it crashes in under 
> > > 5 minutes).

For the crash, you might try enabling CONFIG_DEBUG_ENTRY and seeing if
that gives you any output.

> > > I did see these in the logs which I don't think I've seen before.
> > > 
> > > WARNING: stack recursion on stack type 2
> > > WARNING: can't dereference iret registers at 000000000783fea8 for ip paranoid_entry+0x2e/0x90
> > > WARNING: can't dereference registers at 00000000f0698d17 for ip paranoid_entry+0x4c/0x90
> > > WARNING: stack going in the wrong direction? ip=native_sched_clock+0x9/0x90

This all looks very weird.  The stack pointers -- 000000000783fea8 and
00000000f0698d17 -- are obviously very wrong.  I will try to recreate
locally.

-- 
Josh