linux-kernel - Re: [tip:perf/core] perf/core: Check return value of the perf_event

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Date:   Mon, 29 Aug 2016 09:14:46 -0400 (EDT)
From:   Vince Weaver <vincent.weaver@...ne.edu>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     Jiri Olsa <jolsa@...hat.com>,
        Vegard Nossum <vegard.nossum@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Stephane Eranian <eranian@...gle.com>,
        Vince Weaver <vincent.weaver@...ne.edu>,
        Ingo Molnar <mingo@...nel.org>,
        David Carrillo-Cisneros <davidcc@...gle.com>,
        "H. Peter Anvin" <hpa@...or.com>, Kan Liang <kan.liang@...el.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Paul Turner <pjt@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perf/core] perf/core: Check return value of the perf_event_read()
 IPI

On Mon, 29 Aug 2016, Peter Zijlstra wrote:

> 
> The best I can come up with is something like:
> 
> 
> 	do {
> 		state = READ_ONCE(event->state);
> 		if (state != ACTIVE)
> 			break;
> 		smp_rmb();
> 		cpu = READ_ONCE(event->cpu);
> 		smp_rmb();
> 	} while (READ_ONCE(event->state) != state);
> 
> 
> And I suppose perf_event_restart() should do the same thing... Let me
> ponder this a wee bit more.

the perf_fuzzer trips over this warning fairly regularly too, so once you 
have a patch you're happy with I can give it a test.  

I ordered a whole crate of null modem cables so I've got a whole bunch of 
serial consoles ready and raring to go.  Maybe I can find out how the 
fuzzer crashes the new skylake machine, it doesn't leave anything useful 
in the syslog.

Vince