linux-kernel - Re: [PATCH V6 21/26] coresight: etm-perf: new PMU driver for ETM tracers

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Date:	Fri, 11 Dec 2015 17:18:46 +0200
From:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:	Mathieu Poirier <mathieu.poirier@...aro.org>,
	gregkh@...uxfoundation.org
Cc:	zhang.chunyan@...aro.org, mike.leach@....com, tor@...com,
	al.grant@....com, fainelli@...adcom.com,
	linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Mathieu Poirier <mathieu.poirier@...aro.org>
Subject: Re: [PATCH V6 21/26] coresight: etm-perf: new PMU driver for ETM tracers

Mathieu Poirier <mathieu.poirier@...aro.org> writes:

> +static void etm_event_start(struct perf_event *event, int flags)
> +{
> +	int cpu = smp_processor_id();
> +	struct etm_cpu_data *cpu_data;
> +	struct etm_event_data *event_data;
> +	struct perf_output_handle *handle = this_cpu_ptr(&ctx_handle);
> +	struct coresight_device *sink, *csdev = per_cpu(csdev_src, cpu);
> +
> +	if (!csdev)
> +		goto fail;
> +
> +	/*
> +	 * Deal with the ring buffer API and get a handle on the
> +	 * session's information.
> +	 */
> +	event_data = perf_aux_output_begin(handle, event);
> +	if (WARN_ON_ONCE(!event_data))
> +		goto fail;

Hmm, perf_aux_output_begin() returning NULL is not WARN-worthy and is
actually a normal situation, for example, if the buffer is not
configured yet (which like I suggested in the other email should be a
separate thing from the *event* configuration).

perf_aux_output_begin() will also return NULL if there's no room in the
buffer.

Regards,
--
Alex
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