Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering

[Peter Zijlstra <peterz@infradead.org>]

On Fri, Dec 11, 2015 at 03:36:36PM +0200, Alexander Shishkin wrote:
> +static int
> +perf_event_set_itrace_filter(struct perf_event *event, char *filter_str)
> +{
> +	int ret = 0;
> +
> +	/*
> +	 * Since this is called in perf_ioctl() path, we're already holding
> +	 * ctx::mutex.
> +	 */
> +	lockdep_assert_held(&event->ctx->mutex);
> +
> +	/*
> +	 * For now, we only support filtering in per-task events; doing so
> +	 * for cpu-wide events requires additional context switching trickery,
> +	 * since same object code will be mapped at different virtual
> +	 * addresses in different processes.
> +	 */
> +	if (!event->ctx->task)
> +		return -EOPNOTSUPP;
> +
> +	/* remove existing filters, if any */
> +	perf_itrace_filters_clear(event);
> +
> +	ret = perf_event_parse_itrace_filter(event, filter_str);
> +	if (!ret) {
> +		perf_itrace_filters_apply(event);
> +
> +		ret = perf_event_itrace_filters_setup(event);
> +		if (ret)
> +			perf_itrace_filters_clear(event);

This is what I meant, if you try and set a 'wrong' filter while it
already has filters set, you'll not only error out, you'll also wipe the
current state.

This seems wrong.

> +	}
> +
> +	return ret;
> +}