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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20150805162152.GC25159@twins.programming.kicks-ass.net>
Date:	Wed, 5 Aug 2015 18:21:52 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Alexei Starovoitov <ast@...mgrid.com>
Cc:	Kaixu Xia <xiakaixu@...wei.com>, 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 Wed, Aug 05, 2015 at 09:08:32AM -0700, Alexei Starovoitov wrote:
> On 8/5/15 6:53 AM, Peter Zijlstra wrote:
> >+	/*
> >+	 * If the event is currently on this CPU, its either a per-task event,
> >+	 * or local to this CPU. Furthermore it means its ACTIVE (otherwise
> >+	 * oncpu == -1).
> >+	 */
> >+	if (event->oncpu == smp_processor_id())
> >+		event->pmu->read(event);
> >+
> >+	val = local64_read(&event->count);
> >+	local_irq_restore(flags);
> >+
> 
> nice! cleaner and faster.
> so raw_spin_lock(&ctx->lock) is not needed, because
> update_*(event) methods are not called, right?

Indeed, and by ensuring the event is indeed local (by force of WARN_ON)
disabling IRQs will avoid counter scheduling and result in a stable
event state.


--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html