linux-kernel - [PATCH] perf/core: restore mmap record type correctly

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Message-Id: <20190307185233.225521-1-eranian@google.com>
Date:   Thu,  7 Mar 2019 10:52:33 -0800
From:   Stephane Eranian <eranian@...gle.com>
To:     linux-kernel@...r.kernel.org
Cc:     ak@...ux.intel.com, kan.liang@...el.com, peterz@...radead.org,
        mingo@...e.hu, acme@...hat.com, jolsa@...hat.com
Subject: [PATCH] perf/core: restore mmap record type correctly

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@...gle.com>
---
 kernel/events/core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 5f59d848171e..f170cd12beed 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7188,6 +7188,7 @@ 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))
@@ -7231,6 +7232,7 @@ 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)
-- 
2.21.0.360.g471c308f928-goog