Re: [PATCH v6 3/4] bpf: Implement function bpf_perf_event_read() that get the selected hardware PMU conuter

[Alexei Starovoitov]

On 8/5/15 3:04 AM, Peter Zijlstra wrote:
> > >+	__perf_event_read(event);
> > >+	return perf_event_count(event);
> > >+}
> Also, you probably want a WARN_ON(in_nmi()) there, this function is
> _NOT_  NMI safe.

we check that very early on:
unsigned int trace_call_bpf(struct bpf_prog *prog, void *ctx)
{
        unsigned int ret;

        if (in_nmi()) /* not supported yet */
                return 1;
...

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