perf evsel: Add a backpointer to the evlist a evsel is in

So that functions that deal primarily with an evsel to access
information that concerns the whole evlist it is in.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1440677263-21954-5-git-send-email-kan.liang@intel.com
Signed-off-by: Kan Liang <kan.liang@intel.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index b096ef7..bac25f4 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -206,6 +206,7 @@
 	evsel->leader	   = evsel;
 	evsel->unit	   = "";
 	evsel->scale	   = 1.0;
+	evsel->evlist	   = NULL;
 	INIT_LIST_HEAD(&evsel->node);
 	INIT_LIST_HEAD(&evsel->config_terms);
 	perf_evsel__object.init(evsel);
@@ -1026,6 +1027,7 @@
 void perf_evsel__exit(struct perf_evsel *evsel)
 {
 	assert(list_empty(&evsel->node));
+	assert(evsel->evlist == NULL);
 	perf_evsel__free_fd(evsel);
 	perf_evsel__free_id(evsel);
 	perf_evsel__free_config_terms(evsel);