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

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Date:	Wed, 5 Aug 2015 08:59:36 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Kaixu Xia <xiakaixu@...wei.com>
Cc:	davem@...emloft.net, acme@...nel.org, mingo@...hat.com,
	masami.hiramatsu.pt@...achi.com, jolsa@...nel.org,
	daniel@...earbox.net, wangnan0@...wei.com,
	linux-kernel@...r.kernel.org, pi3orama@....com, hekuang@...wei.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH v6 3/4] bpf: Implement function bpf_perf_event_read() that
 get the selected hardware PMU conuter

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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