Re: [tip:perf/core] perf/core: Check return value of the perf_event_read() IPI

[Vince Weaver]

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