Commit-ID: 4738ca30b4a7a113084d7863846175094f95c62f Gitweb: http://git.kernel.org/tip/4738ca30b4a7a113084d7863846175094f95c62f Author: Arnaldo Carvalho de Melo <a...@redhat.com> AuthorDate: Thu, 23 Feb 2017 13:24:34 -0300 Committer: Arnaldo Carvalho de Melo <a...@redhat.com> CommitDate: Fri, 3 Mar 2017 19:07:16 -0300
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.hun...@intel.com> Cc: David Ahern <dsah...@gmail.com> Cc: Elena Reshetova <elena.reshet...@intel.com> Cc: Jiri Olsa <jo...@kernel.org> Cc: Namhyung Kim <namhy...@kernel.org> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Wang Nan <wangn...@huawei.com> Link: http://lkml.kernel.org/r/20170223162344.gd3...@kernel.org Signed-off-by: Arnaldo Carvalho de Melo <a...@redhat.com> --- tools/perf/util/evlist.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c index 564b924..50420cd 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; }
