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

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Message-ID: <55C2332B.3010708@plumgrid.com>
Date:	Wed, 5 Aug 2015 09:00:43 -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 3:15 AM, Peter Zijlstra wrote:
> On Wed, Aug 05, 2015 at 12:04:25PM +0200, Peter Zijlstra wrote:
>> On Tue, Aug 04, 2015 at 08:58:15AM +0000, Kaixu Xia wrote:
>
>>> +	    event->ctx->task != current)
>
> Strictly speaking we should hold rcu_read_lock around dereferencing
> event->ctx (or have IRQs disabled -- although I know Paul doesn't like
> us relying on that).

programs are always executing under rcu_read_lock, so we should be good
here too.

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