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

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Date:   Thu, 11 Jan 2018 15:43:41 -0500 (EST)
From:   Vince Weaver <vincent.weaver@...ne.edu>
To:     Vince Weaver <vincent.weaver@...ne.edu>
cc:     Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        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, 11 Jan 2018, Vince Weaver wrote:

> 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 can confirm this, I am able to trigger the stack recursion warning even 
when "pti=off" is set.

Jan 11 15:34:47 core2 kernel: [  320.668900] WARNING: stack recursion on stack type 4
Jan 11 15:34:47 core2 kernel: [  320.668909] WARNING: can't dereference registers at 00000000d5ae0491 for ip swapgs_restore_regs_and_return_to_usermode+0x28/0x7c

Vince