perf/core: Restore mmap record type correctly [Linux 3.16.72]

This Linux kernel change "perf/core: Restore mmap record type correctly" is included in the Linux 3.16.72 release. This change is authored by Stephane Eranian <eranian [at] google.com> on Thu Mar 7 10:52:33 2019 -0800. The commit for this change in Linux stable tree is fcd707d (patch) which is from upstream commit d9c1bb2. The same Linux upstream change may have been applied to various maintained Linux releases and you can find all Linux releases containing changes from upstream d9c1bb2.

perf/core: Restore mmap record type correctly

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 <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Kan Liang <[email protected]>
Fixes: 13d7a2410fa6 ("perf: Add attr->mmap2 attribute to an event")
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>
Signed-off-by: Ben Hutchings <[email protected]>

There are 2 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 kernel/events/core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index e8be529..3beed0e 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5445,6 +5445,7 @@ static void perf_event_mmap_output(struct perf_event *event,
    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(struct perf_event *event,
    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)

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