diff options
| author | Arnaldo Carvalho de Melo | 2017-02-23 13:24:34 -0300 |
|---|---|---|
| committer | Arnaldo Carvalho de Melo | 2017-03-03 19:07:16 -0300 |
| commit | 4738ca30b4a7a113084d7863846175094f95c62f (patch) | |
| tree | 838fdd3b49d186f5fda9b23ab567e003c0634567 | |
| parent | 364fed351369e0193244fa2c78df855724cdddb9 (diff) | |
perf evlist: Clarify a bit the use of perf_mmap->refcnt
This is an odd refcount use case, so add some more comments to help
understand that when it hits zero it really means that the mmap()ed area
(on a perf_event_open() returned fd) has been munmap()ed.
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Elena Reshetova <elena.reshetova@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/20170223162344.GD3595@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
| -rw-r--r-- | tools/perf/util/evlist.c | 13 |
1 files changed, 12 insertions, 1 deletions
diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c index 564b924fb48a..50420cd35446 100644 --- a/tools/perf/util/evlist.c +++ b/tools/perf/util/evlist.c @@ -974,8 +974,19 @@ static struct perf_mmap *perf_evlist__alloc_mmap(struct perf_evlist *evlist) if (!map) return NULL; - for (i = 0; i < evlist->nr_mmaps; i++) + for (i = 0; i < evlist->nr_mmaps; i++) { map[i].fd = -1; + /* + * When the perf_mmap() call is made we grab one refcount, plus + * one extra to let perf_evlist__mmap_consume() get the last + * events after all real references (perf_mmap__get()) are + * dropped. + * + * Each PERF_EVENT_IOC_SET_OUTPUT points to this mmap and + * thus does perf_mmap__get() on it. + */ + refcount_set(&map[i].refcnt, 0); + } return map; } |