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From: Vince Weaver <vincent.weaver@maine.edu>
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Date: Thu, 11 Jan 2018 14:57:25 -0500 (EST)
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To: Peter Zijlstra <peterz@infradead.org>
cc: Josh Poimboeuf <jpoimboe@redhat.com>,
        Vince Weaver <vincent.weaver@maine.edu>,
        Ingo Molnar <mingo@kernel.org>, linux-kernel@vger.kernel.org,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andy Lutomirski <luto@kernel.org>
Subject: Re: perf: perf_fuzzer quickly locks up on 4.15-rc7
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On Thu, 11 Jan 2018, Peter Zijlstra wrote:

> 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 think I have hit those errors even with pti disabled but now I'll have 
to double check.

> > 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.

I can only trigger them with perf_event_paranoid=0 (not with 
perf_event_paranoid=2) so it might depend on how much of the PMU is 
virtualized.

Vince