perf evlist: Make event_copy local to mmaps

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: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1360098762-61827-1-git-send-email-dsahern@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

3 files changed, 30 insertions, 29 deletions

diff --git a/tools/perf/perf.h b/tools/perf/perf.h
index 8f3bf388e414..c2206c87fc9f 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 ecf123e080bb..bc4ad7977438 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -375,7 +375,7 @@ 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);
@@ -385,7 +385,7 @@ 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 73579a25a93e..2dd07bd60b4f 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 */