linux-kernel - Re: [PATCH v5 1/4] ftrace: Implement fs notification for tracing_max

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Date:   Wed, 4 Sep 2019 07:39:15 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Viktor Rosendahl <viktor.rosendahl@...il.com>
Cc:     Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        Joel Fernandes <joel@...lfernandes.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v5 1/4] ftrace: Implement fs notification for
 tracing_max_latency

On Tue,  3 Sep 2019 15:25:59 +0200
Viktor Rosendahl <viktor.rosendahl@...il.com> wrote:

> +void latency_fsnotify_stop(void)
> +{
> +	/* Make sure all CPUs see caller's previous actions to stop tracer */
> +	smp_wmb();

These memory barriers just look wrong. What exactly are you trying to protect here?

Where's the matching rmbs?

-- Steve

> +	static_branch_disable(&latency_notify_key);
> +	latency_fsnotify_process();
> +}
> +
> +void latency_fsnotify_start(void)
> +{
> +	static_branch_enable(&latency_notify_key);
> +	/* Make sure all CPUs see key value before caller continue */
> +	smp_wmb();
> +}
> +