netdev - Re: [PATCH V5 1/1] bpf: control events stored in PERF_EVENT_ARRAY maps trace data output when perf sampling

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Date:	Wed, 21 Oct 2015 22:01:46 +0800
From:	pi3orama <pi3orama@....com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	"Wangnan (F)" <wangnan0@...wei.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	xiakaixu <xiakaixu@...wei.com>, davem@...emloft.net,
	acme@...nel.org, mingo@...hat.com, masami.hiramatsu.pt@...achi.com,
	jolsa@...nel.org, daniel@...earbox.net,
	linux-kernel@...r.kernel.org, hekuang@...wei.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH V5 1/1] bpf: control events stored in PERF_EVENT_ARRAY maps trace data output when perf sampling



发自我的 iPhone

> 在 2015年10月21日，下午9:49，Peter Zijlstra <peterz@...radead.org> 写道：
> 
>> On Wed, Oct 21, 2015 at 09:42:12PM +0800, Wangnan (F) wrote:
>> How can an eBPF program access a !local event:
>> 
>> when creating perf event array we don't care which perf event
>> is for which CPU, so perf program can access any perf event in
>> that array.
> 
> So what is stopping the eBPF thing from calling perf_event_read_local()
> on a !local event and triggering a kernel splat?

I can understand the perf_event_read_local() case, but I really can't understand
what is stopping us to write to an atomic field belong to a !local perf event.
Could you please give a further explanation?

Thank you.
> 

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