Commit 4738ca30 authored Feb 23, 2017 by Arnaldo Carvalho de Melo

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>

parent 364fed35

tools/perf/util/evlist.c

+12 −1

Original line number	Diff line number	Diff line
		@@ -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;
		}