[PATCH 2/9] lib/ref_tracker: compact stacktraces before printing

[Andrzej Hajda]

In cases references are taken alternately on multiple exec paths leak
report can grow substantially, sorting and grouping leaks by stack_handle
allows to compact it.

Signed-off-by: Andrzej Hajda <andrzej.hajda at intel.com>
Reviewed-by: Chris Wilson <chris.p.wilson at intel.com>
---
 lib/ref_tracker.c | 35 +++++++++++++++++++++++++++--------
 1 file changed, 27 insertions(+), 8 deletions(-)

diff --git a/lib/ref_tracker.c b/lib/ref_tracker.c
index 1b0c6d645d64a..0e9c7d2828ccb 100644
--- a/lib/ref_tracker.c
+++ b/lib/ref_tracker.c
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0-or-later
 #include <linux/export.h>
+#include <linux/list_sort.h>
 #include <linux/ref_tracker.h>
 #include <linux/slab.h>
 #include <linux/stacktrace.h>
@@ -14,23 +15,41 @@ struct ref_tracker {
 	depot_stack_handle_t	free_stack_handle;
 };
 
+static int ref_tracker_cmp(void *priv, const struct list_head *a, const struct list_head *b)
+{
+	const struct ref_tracker *ta = list_entry(a, const struct ref_tracker, head);
+	const struct ref_tracker *tb = list_entry(b, const struct ref_tracker, head);
+
+	return ta->alloc_stack_handle - tb->alloc_stack_handle;
+}
+
 void __ref_tracker_dir_print(struct ref_tracker_dir *dir,
 			   unsigned int display_limit)
 {
+	unsigned int i = 0, count = 0;
 	struct ref_tracker *tracker;
-	unsigned int i = 0;
+	depot_stack_handle_t stack;
 
 	lockdep_assert_held(&dir->lock);
 
+	if (list_empty(&dir->list))
+		return;
+
+	list_sort(NULL, &dir->list, ref_tracker_cmp);
+
 	list_for_each_entry(tracker, &dir->list, head) {
-		if (i < display_limit) {
-			pr_err("leaked reference.\n");
-			if (tracker->alloc_stack_handle)
-				stack_depot_print(tracker->alloc_stack_handle);
-			i++;
-		} else {
+		if (i++ >= display_limit)
 			break;
-		}
+		if (!count++)
+			stack = tracker->alloc_stack_handle;
+		if (stack == tracker->alloc_stack_handle &&
+		    !list_is_last(&tracker->head, &dir->list))
+			continue;
+
+		pr_err("leaked %d references.\n", count);
+		if (stack)
+			stack_depot_print(stack);
+		count = 0;
 	}
 }
 EXPORT_SYMBOL(__ref_tracker_dir_print);
-- 
2.25.1