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

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Message-ID: <87bn9wykhy.fsf@ashishki-desk.ger.corp.intel.com>
Date:	Fri, 11 Dec 2015 19:15:37 +0200
From:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	vince@...ter.net, eranian@...gle.com,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Mathieu Poirier <mathieu.poirier@...aro.org>
Subject: Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering

Peter Zijlstra <peterz@...radead.org> writes:

> 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.

Ah, now I see what you mean. Yes, you're right.

Regards,
--
Alex
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