[PATCH 3.16 007/157] perf/core: Restore mmap record type correctly

[Ben Hutchings]

3.16.72-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Stephane Eranian <eranian@xxxxxxxxxx>

commit d9c1bb2f6a2157b38e8eb63af437cb22701d31ee upstream.

On mmap(), perf_events generates a RECORD_MMAP record and then checks
which events are interested in this record. There are currently 2
versions of mmap records: RECORD_MMAP and RECORD_MMAP2. MMAP2 is larger.
The event configuration controls which version the user level tool
accepts.

If the event->attr.mmap2=1 field then MMAP2 record is returned.  The
perf_event_mmap_output() takes care of this. It checks attr->mmap2 and
corrects the record fields before putting it in the sampling buffer of
the event.  At the end the function restores the modified MMAP record
fields.

The problem is that the function restores the size but not the type.
Thus, if a subsequent event only accepts MMAP type, then it would
instead receive an MMAP2 record with a size of MMAP record.

This patch fixes the problem by restoring the record type on exit.

Signed-off-by: Stephane Eranian <eranian@xxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
Fixes: 13d7a2410fa6 ("perf: Add attr->mmap2 attribute to an event")
Link: http://lkml.kernel.org/r/20190307185233.225521-1-eranian@xxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 kernel/events/core.c | 2 ++
 1 file changed, 2 insertions(+)

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5445,6 +5445,7 @@ static void perf_event_mmap_output(struc
 	struct perf_output_handle handle;
 	struct perf_sample_data sample;
 	int size = mmap_event->event_id.header.size;
+	u32 type = mmap_event->event_id.header.type;
 	int ret;
 
 	if (!perf_event_mmap_match(event, data))
@@ -5488,6 +5489,7 @@ static void perf_event_mmap_output(struc
 	perf_output_end(&handle);
 out:
 	mmap_event->event_id.header.size = size;
+	mmap_event->event_id.header.type = type;
 }
 
 static void perf_event_mmap_event(struct perf_mmap_event *mmap_event)