Mathieu Poirier <mathieu.poirier@xxxxxxxxxx> writes:
> +static int etm_event_init(struct perf_event *event)
> +{
> + if (event->attr.type != etm_pmu.type)
> + return -ENOENT;
> +
> + if (event->cpu >= nr_cpu_ids)
> + return -EINVAL;
perf_event_alloc() already does this. Except for this one doesn't cover
the negative space.
[snip]
> +static void etm_free_aux(void *data)
> +{
> + struct etm_event_data *event_data = data;
> +
> + pr_err("Queing work\n");
Probably not pr_err().
> + schedule_work(&event_data->work);
> +}
[snip]
> +static void etm_event_start(struct perf_event *event, int flags)
> +{
> + int cpu = smp_processor_id();
> + 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;
There really shouldn't be a warning here. I understand that the 'no
buffer' case is taped over by the !csdev check above, but there are
other ligitimate reasons for perf_aux_output_begin() to return NULL,
like no-space-left.
> +
> + /* We need a sink, no need to continue without one */
> + sink = coresight_get_sink(event_data->path[cpu]);
> + if (!sink || !sink_ops(sink)->set_buffer)
> + goto fail_end_stop;
Is this possible after the coresight_build_path() things in setup_aux?
Might be a better candidate for WARN_*ONCE().
> +
> + /* Configure the sink */
> + if (sink_ops(sink)->set_buffer(sink, handle,
> + event_data->snk_config))
> + goto fail_end_stop;
> +
> + /* Nothing will happen without a path */
> + if (coresight_enable_path(event_data->path[cpu], CS_MODE_PERF))
> + goto fail_end_stop;
I'd like to understand all the potential failures here, because it's
really a good idea to keep those to a minimum for the sake of
consistency. That is, if the user succeeded in creating an event, about
the only good reason for the event not starting is a filled up buffer.
This is why it makes a lot of sense to keep all the
coresight_build_path()/coresight_enable_path() to the .event_init()
phase and let them fail early, if they should fail.
Regards,
--
Alex
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