linux-kernel - [PATCH 3.16.y-ckt 155/180] perf/x86: Fix filter

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Message-Id: <1454538786-12215-156-git-send-email-luis.henriques@canonical.com>
Date:	Wed,  3 Feb 2016 22:32:41 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Stephane Eranian <eranian@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Vince Weaver <vincent.weaver@...ne.edu>, jolsa@...nel.org,
	kan.liang@...el.com, Ingo Molnar <mingo@...nel.org>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 155/180] perf/x86: Fix filter_events() bug with event mappings

3.16.7-ckt24 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Stephane Eranian <eranian@...gle.com>

commit 61b87cae6361ea6af161c1ffa549898892707b19 upstream.

This patch fixes a bug in the filter_events() function.

The patch fixes the bug whereby if some mappings did not
exist, e.g., STALLED_CYCLES_FRONTEND, then any event after it
in the attrs array would disappear from the published list of
events in /sys/devices/cpu/events. This could be verified
easily on any system post SNB (which do not publish
STALLED_CYCLES_FRONTEND):

	$ ./perf stat -e cycles,ref-cycles true
	Performance counter stats for 'true':
              1,217,348      cycles
	<not supported>      ref-cycles

The problem is that in filter_events() there is an assumption
that the argument (attrs) is organized in increasing continuous
event indexes related to the event_map(). But if we remove the
non-supported events by shifing the position in the array, then
the lookup x86_pmu.event_map() needs to compensate for it, otherwise
we are looking up the wrong index. This patch corrects this problem
by compensating for the deleted events and with that ref-cycles
reappears (here shown on Haswell):

	$ perf stat -e ref-cycles,cycles true
	Performance counter stats for 'true':
         4,525,910      ref-cycles
         1,064,920      cycles
       0.002943888 seconds time elapsed

Signed-off-by: Stephane Eranian <eranian@...gle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Vince Weaver <vincent.weaver@...ne.edu>
Cc: jolsa@...nel.org
Cc: kan.liang@...el.com
Fixes: 8300daa26755 ("perf/x86: Filter out undefined events from sysfs events attribute")
Link: http://lkml.kernel.org/r/1449516805-6637-1-git-send-email-eranian@google.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 arch/x86/kernel/cpu/perf_event.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 2a6c3859e8a1..7c08f55a07cd 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -1386,6 +1386,7 @@ static void __init filter_events(struct attribute **attrs)
 {
 	struct device_attribute *d;
 	struct perf_pmu_events_attr *pmu_attr;
+	int offset = 0;
 	int i, j;
 
 	for (i = 0; attrs[i]; i++) {
@@ -1394,7 +1395,7 @@ static void __init filter_events(struct attribute **attrs)
 		/* str trumps id */
 		if (pmu_attr->event_str)
 			continue;
-		if (x86_pmu.event_map(i))
+		if (x86_pmu.event_map(i + offset))
 			continue;
 
 		for (j = i; attrs[j]; j++)
@@ -1402,6 +1403,14 @@ static void __init filter_events(struct attribute **attrs)
 
 		/* Check the shifted attr. */
 		i--;
+
+		/*
+		 * event_map() is index based, the attrs array is organized
+		 * by increasing event index. If we shift the events, then
+		 * we need to compensate for the event_map(), otherwise
+		 * we are looking up the wrong event in the map
+		 */
+		offset++;
 	}
 }