[PATCH 2/2] perf top: Fix event group with more than two events

[Namhyung Kim]

The event group feature links relevant hist entries among events so
that they can be displayed together.  During the link process, each
hist entry in non-leader events is connected to a hist entry in the
leader event.  This is done in order of events specified in the
command line so it assumes that events are linked in the order.

But perf top can break the assumption since it does the link process
multiple times.  For example, a hist entry can be in the third event
only at first so it's linked after the leader.  Some time later,
second event has a hist entry for it and it'll be linked after the
entry of the third event.

This makes the code compilicated to deal with such unordered entries.
This patch simply unlink all the entries after it's printed so that
they can assume the correct order after the repeated link process.
Also it'd be easy to deal with decaying old entries IMHO.

Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
---
 tools/perf/builtin-top.c |  6 ++++++
 tools/perf/util/hist.c   | 39 +++++++++++++++++++++------------------
 tools/perf/util/hist.h   |  1 +
 3 files changed, 28 insertions(+), 18 deletions(-)

diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
index 9d3059d2029d..b871dd72e4bd 100644
--- a/tools/perf/builtin-top.c
+++ b/tools/perf/builtin-top.c
@@ -272,6 +272,12 @@ static void evlist__resort_hists(struct perf_top *t)
 	evlist__for_each_entry(evlist, pos) {
 		struct hists *hists = evsel__hists(pos);
 
+		/*
+		 * unlink existing entries so that they can be linked
+		 * in a correct order in hists__match() below.
+		 */
+		hists__unlink(hists);
+
 		if (evlist->enabled) {
 			if (t->zero) {
 				hists__delete_entries(hists);
diff --git a/tools/perf/util/hist.c b/tools/perf/util/hist.c
index 8efbf58dc3d0..47401210e087 100644
--- a/tools/perf/util/hist.c
+++ b/tools/perf/util/hist.c
@@ -2436,7 +2436,7 @@ void hists__match(struct hists *leader, struct hists *other)
 {
 	struct rb_root_cached *root;
 	struct rb_node *nd;
-	struct hist_entry *pos, *pair, *pos_pair, *tmp_pair;
+	struct hist_entry *pos, *pair;
 
 	if (symbol_conf.report_hierarchy) {
 		/* hierarchy report always collapses entries */
@@ -2453,24 +2453,8 @@ void hists__match(struct hists *leader, struct hists *other)
 		pos  = rb_entry(nd, struct hist_entry, rb_node_in);
 		pair = hists__find_entry(other, pos);
 
-		if (pair && list_empty(&pair->pairs.node)) {
-			list_for_each_entry_safe(pos_pair, tmp_pair, &pos->pairs.head, pairs.node) {
-				if (pos_pair->hists == other) {
-					/*
-					 * XXX maybe decayed entries can appear
-					 * here?  but then we would have use
-					 * after free, as decayed entries are
-					 * freed see hists__delete_entry
-					 */
-					BUG_ON(!pos_pair->dummy);
-					list_del_init(&pos_pair->pairs.node);
-					hist_entry__delete(pos_pair);
-					break;
-				}
-			}
-
+		if (pair)
 			hist_entry__add_pair(pair, pos);
-		}
 	}
 }
 
@@ -2555,6 +2539,25 @@ int hists__link(struct hists *leader, struct hists *other)
 	return 0;
 }
 
+int hists__unlink(struct hists *hists)
+{
+	struct rb_root_cached *root;
+	struct rb_node *nd;
+	struct hist_entry *pos;
+
+	if (hists__has(hists, need_collapse))
+		root = &hists->entries_collapsed;
+	else
+		root = hists->entries_in;
+
+	for (nd = rb_first_cached(root); nd; nd = rb_next(nd)) {
+		pos = rb_entry(nd, struct hist_entry, rb_node_in);
+		list_del_init(&pos->pairs.node);
+	}
+
+	return 0;
+}
+
 void hist__account_cycles(struct branch_stack *bs, struct addr_location *al,
 			  struct perf_sample *sample, bool nonany_branch_mode)
 {
diff --git a/tools/perf/util/hist.h b/tools/perf/util/hist.h
index 83d5fc15429c..7b9267ebebeb 100644
--- a/tools/perf/util/hist.h
+++ b/tools/perf/util/hist.h
@@ -217,6 +217,7 @@ void hists__calc_col_len(struct hists *hists, struct hist_entry *he);
 
 void hists__match(struct hists *leader, struct hists *other);
 int hists__link(struct hists *leader, struct hists *other);
+int hists__unlink(struct hists *hists);
 
 struct hists_evsel {
 	struct evsel evsel;
-- 
2.23.0.187.g17f5b7556c-goog