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

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Date:   Thu, 11 Jan 2018 20:50:18 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
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 Thu, Jan 11, 2018 at 01:21:12PM -0600, Josh Poimboeuf wrote:
> Yuck.  This time it was stack recursion on the entry stack.  In the
> previous error, recursion was detected on the IRQ stack.  Otherwise they
> look quite similar.
> 
> Was that also with nopti?

Both with pti enabled, nopti makes things work again.

> I haven't had a chance to try it yet, any idea if these would be
> recreatable in a VM?

Good question; typically we run the perf fuzzer on read hardware because
the PMU doesn't virtualize much. But if software perf is enough to
trigger this, that would certainly help.