[PATCH 4.2.y-ckt 219/268] perf/x86: Fix filter_events() bug with event mappings

From: Kamal Mostafa
Date: Wed Jan 27 2016 - 15:40:42 EST

4.2.8-ckt3 -stable review patch. If anyone has any objections, please let me know.


From: Stephane Eranian <eranian@xxxxxxxxxx>

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easily on any system post SNB (which do not publish

$ ./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@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Vince Weaver <vincent.weaver@xxxxxxxxx>
Cc: jolsa@xxxxxxxxxx
Cc: kan.liang@xxxxxxxxx
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@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
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 9469dfa..a27d738 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -1531,6 +1531,7 @@ 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++) {
@@ -1539,7 +1540,7 @@ static void __init filter_events(struct attribute **attrs)
/* str trumps id */
if (pmu_attr->event_str)
- if (x86_pmu.event_map(i))
+ if (x86_pmu.event_map(i + offset))

for (j = i; attrs[j]; j++)
@@ -1547,6 +1548,14 @@ static void __init filter_events(struct attribute **attrs)

/* Check the shifted attr. */
+ /*
+ * 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++;