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Subject[PATCH] perf: make event_copy local to mmaps
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I am getting segfaults *after* the time sorting of perf samples where
the event type is off the charts:

(gdb) bt
\#0 0x0807b1b2 in hists__inc_nr_events (hists=0x80a99c4, type=1163281902) at util/hist.c:1225
\#1 0x08070795 in perf_session_deliver_event (session=0x80a9b90, event=0xf7a6aff8, sample=0xffffc318, tool=0xffffc520,
file_offset=0) at util/session.c:884
\#2 0x0806f9b9 in flush_sample_queue (s=0x80a9b90, tool=0xffffc520) at util/session.c:555
\#3 0x0806fc53 in process_finished_round (tool=0xffffc520, event=0x0, session=0x80a9b90) at util/session.c:645

This is bizarre because the event has already been processed once --
before it was added to the samples queue -- and the event was found to
be sane at that time.

There seem to be 2 causes:
1. perf_evlist__mmap_read updates the read location even though there
are outstanding references to events sitting in the mmap buffers via the
ordered samples queue.

2. There is a single evlist->event_copy for all evlist entries. event_copy
is used to handle an event wrapping at the mmap buffer boundary.

This patch addresses the second problem - making event_copy local to each
perf_mmap. With this change my highly repeatable use case no longer fails.

The first problem is much more complicated and will be the subject of a
future patch.

Signed-off-by: David Ahern <dsahern@gmail.com>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
---
tools/perf/perf.h | 26 --------------------------
tools/perf/util/evlist.c | 4 ++--
tools/perf/util/evlist.h | 29 ++++++++++++++++++++++++++++-
3 files changed, 30 insertions(+), 29 deletions(-)

diff --git a/tools/perf/perf.h b/tools/perf/perf.h
index 8f3bf38..c2206c8 100644
--- a/tools/perf/perf.h
+++ b/tools/perf/perf.h
@@ -103,32 +103,6 @@
#include "util/types.h"
#include <stdbool.h>

-struct perf_mmap {
- void *base;
- int mask;
- unsigned int prev;
-};
-
-static inline unsigned int perf_mmap__read_head(struct perf_mmap *mm)
-{
- struct perf_event_mmap_page *pc = mm->base;
- int head = pc->data_head;
- rmb();
- return head;
-}
-
-static inline void perf_mmap__write_tail(struct perf_mmap *md,
- unsigned long tail)
-{
- struct perf_event_mmap_page *pc = md->base;
-
- /*
- * ensure all reads are done before we write the tail out.
- */
- /* mb(); */
- pc->data_tail = tail;
-}
-
/*
* prctl(PR_TASK_PERF_EVENTS_DISABLE) will (cheaply) disable all
* counters in the current task.
diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index eddd5eb..8fe4e52 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -376,7 +376,7 @@ union perf_event *perf_evlist__mmap_read(struct perf_evlist *evlist, int idx)
if ((old & md->mask) + size != ((old + size) & md->mask)) {
unsigned int offset = old;
unsigned int len = min(sizeof(*event), size), cpy;
- void *dst = &evlist->event_copy;
+ void *dst = &md->event_copy;

do {
cpy = min(md->mask + 1 - (offset & md->mask), len);
@@ -386,7 +386,7 @@ union perf_event *perf_evlist__mmap_read(struct perf_evlist *evlist, int idx)
len -= cpy;
} while (len);

- event = &evlist->event_copy;
+ event = &md->event_copy;
}

old += size;
diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
index 73579a2..2dd07bd 100644
--- a/tools/perf/util/evlist.h
+++ b/tools/perf/util/evlist.h
@@ -17,6 +17,13 @@ struct perf_record_opts;
#define PERF_EVLIST__HLIST_BITS 8
#define PERF_EVLIST__HLIST_SIZE (1 << PERF_EVLIST__HLIST_BITS)

+struct perf_mmap {
+ void *base;
+ int mask;
+ unsigned int prev;
+ union perf_event event_copy;
+};
+
struct perf_evlist {
struct list_head entries;
struct hlist_head heads[PERF_EVLIST__HLIST_SIZE];
@@ -30,7 +37,6 @@ struct perf_evlist {
pid_t pid;
} workload;
bool overwrite;
- union perf_event event_copy;
struct perf_mmap *mmap;
struct pollfd *pollfd;
struct thread_map *threads;
@@ -136,4 +142,25 @@ static inline struct perf_evsel *perf_evlist__last(struct perf_evlist *evlist)
}

size_t perf_evlist__fprintf(struct perf_evlist *evlist, FILE *fp);
+
+static inline unsigned int perf_mmap__read_head(struct perf_mmap *mm)
+{
+ struct perf_event_mmap_page *pc = mm->base;
+ int head = pc->data_head;
+ rmb();
+ return head;
+}
+
+static inline void perf_mmap__write_tail(struct perf_mmap *md,
+ unsigned long tail)
+{
+ struct perf_event_mmap_page *pc = md->base;
+
+ /*
+ * ensure all reads are done before we write the tail out.
+ */
+ /* mb(); */
+ pc->data_tail = tail;
+}
+
#endif /* __PERF_EVLIST_H */
--
1.7.10.1


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