Commit 88abd409 authored May 30, 2017 by Peter Zijlstra Committed by Greg Kroah-Hartman Apr 13, 2018

perf/core: Correct event creation with PERF_FORMAT_GROUP




[ Upstream commit ba5213ae6b88fb170c4771fef6553f759c7d8cdd ]

Andi was asking about PERF_FORMAT_GROUP vs inherited events, which led
to the discovery of a bug from commit:

  3dab77fb ("perf: Rework/fix the whole read vs group stuff")

 -       PERF_SAMPLE_GROUP                       = 1U << 4,
 +       PERF_SAMPLE_READ                        = 1U << 4,

 -       if (attr->inherit && (attr->sample_type & PERF_SAMPLE_GROUP))
 +       if (attr->inherit && (attr->read_format & PERF_FORMAT_GROUP))

is a clear fail :/

While this changes user visible behaviour; it was previously possible
to create an inherited event with PERF_SAMPLE_READ; this is deemed
acceptible because its results were always incorrect.

Reported-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vince@deater.net>
Fixes:  3dab77fb ("perf: Rework/fix the whole read vs group stuff")
Link: http://lkml.kernel.org/r/20170530094512.dy2nljns2uq7qa3j@hirez.programming.kicks-ass.net


Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 85fcf68b

kernel/events/core.c

+10 −5

Original line number	Diff line number	Diff line
		@@ -4861,9 +4861,6 @@ static void perf_output_read_one(struct perf_output_handle *handle,
		__output_copy(handle, values, n * sizeof(u64));
		}

		/*
		* XXX PERF_FORMAT_GROUP vs inherited events seems difficult.
		*/
		static void perf_output_read_group(struct perf_output_handle *handle,
		struct perf_event *event,
		u64 enabled, u64 running)
		@@ -4908,6 +4905,13 @@ static void perf_output_read_group(struct perf_output_handle *handle,
		#define PERF_FORMAT_TOTAL_TIMES (PERF_FORMAT_TOTAL_TIME_ENABLED\|\
		PERF_FORMAT_TOTAL_TIME_RUNNING)

		/*
		* XXX PERF_SAMPLE_READ vs inherited events seems difficult.
		*
		* The problem is that its both hard and excessively expensive to iterate the
		* child list, not to mention that its impossible to IPI the children running
		* on another CPU, from interrupt/NMI context.
		*/
		static void perf_output_read(struct perf_output_handle *handle,
		struct perf_event *event)
		{
		@@ -7194,9 +7198,10 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
		local64_set(&hwc->period_left, hwc->sample_period);

		/*
		* we currently do not support PERF_FORMAT_GROUP on inherited events
		* We currently do not support PERF_SAMPLE_READ on inherited events.
		* See perf_output_read().
		*/
		if (attr->inherit && (attr->read_format & PERF_FORMAT_GROUP))
		if (attr->inherit && (attr->sample_type & PERF_SAMPLE_READ))
		goto err_ns;

		pmu = perf_init_event(event);