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

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Message-ID: <20180109195319.GN6176@hirez.programming.kicks-ass.net>
Date:   Tue, 9 Jan 2018 20:53:19 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.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>
Subject: Re: perf: perf_fuzzer quickly locks up on 4.15-rc7

On Tue, Jan 09, 2018 at 01:09:57PM -0500, Steven Rostedt wrote:
> On Tue, 9 Jan 2018 19:02:07 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > This would globally serialize all perf_ioctl()'s, also that event_mutex
> > is for trace_events and really does not belong in perf.
> > 
> > So no, I really rather would not do this.
> > 
> > The alternative I was thinking of was lifting the cpuhp lock out from
> > under event_mutex, that would also break the chain, but would probably
> > be lots of work for trace bits.
> 
> I think we tried that once, and it became an never ending whack a mole
> process. I prefer not to do that either. 

Figures..

> How bad is your work around patch that you posted?

Not too bad, just tricky..