tracing/ftrace: fix a memory leak in stat tracing

Impact: fix memory leak

This patch fixes a memory leak inside reset_stat_list(). The freeing
loop iterated only once.

Also turn the stat_list into a simple struct list_head, which
simplify the code and avoid an unused static pointer.

Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/trace/trace_stat.c

@@ -21,7 +21,7 @@ struct trace_stat_list {
 	void *stat;
 };
 
-static struct trace_stat_list stat_list;
+static LIST_HEAD(stat_list);
 
 /*
  * This is a copy of the current tracer to avoid racy
@@ -39,22 +39,12 @@ static DEFINE_MUTEX(stat_list_mutex);
 
 static void reset_stat_list(void)
 {
-	struct trace_stat_list *node;
-	struct list_head *next;
+	struct trace_stat_list *node, *next;
 
-	if (list_empty(&stat_list.list))
-		return;
-
-	node = list_entry(stat_list.list.next, struct trace_stat_list, list);
-	next = node->list.next;
-
-	while (&node->list != next) {
+	list_for_each_entry_safe(node, next, &stat_list, list)
 		kfree(node);
-		node = list_entry(next, struct trace_stat_list, list);
-	}
-	kfree(node);
 
-	INIT_LIST_HEAD(&stat_list.list);
+	INIT_LIST_HEAD(&stat_list);
 }
 
 void init_tracer_stat(struct tracer *trace)
@@ -107,7 +97,7 @@ static int stat_seq_init(void)
 	}
 
 	INIT_LIST_HEAD(&new_entry->list);
-	list_add(&new_entry->list, &stat_list.list);
+	list_add(&new_entry->list, &stat_list);
 	new_entry->stat = current_tracer.stat_start();
 
 	prev_stat = new_entry->stat;
@@ -130,7 +120,7 @@ static int stat_seq_init(void)
 		if (!new_entry->stat)
 			break;
 
-		list_for_each_entry(iter_entry, &stat_list.list, list) {
+		list_for_each_entry(iter_entry, &stat_list, list) {
 			/* Insertion with a descendent sorting */
 			if (current_tracer.stat_cmp(new_entry->stat,
 						iter_entry->stat) > 0) {
@@ -141,7 +131,7 @@ static int stat_seq_init(void)
 
 			/* The current smaller value */
 			} else if (list_is_last(&iter_entry->list,
-						&stat_list.list)) {
+						&stat_list)) {
 				list_add(&new_entry->list, &iter_entry->list);
 				break;
 			}
@@ -162,7 +152,7 @@ exit_free_list:
 
 static void *stat_seq_start(struct seq_file *s, loff_t *pos)
 {
-	struct trace_stat_list *l = (struct trace_stat_list *)s->private;
+	struct list_head *l = (struct list_head *)s->private;
 
 	/* Prevent from tracer switch or stat_list modification */
 	mutex_lock(&stat_list_mutex);
@@ -171,14 +161,14 @@ static void *stat_seq_start(struct seq_file *s, loff_t *pos)
 	if (!*pos && current_tracer.stat_headers)
 		current_tracer.stat_headers(s);
 
-	return seq_list_start(&l->list, *pos);
+	return seq_list_start(l, *pos);
 }
 
 static void *stat_seq_next(struct seq_file *s, void *p, loff_t *pos)
 {
-	struct trace_stat_list *l = (struct trace_stat_list *)s->private;
+	struct list_head *l = (struct list_head *)s->private;
 
-	return seq_list_next(p, &l->list, pos);
+	return seq_list_next(p, l, pos);
 }
 
 static void stat_seq_stop(struct seq_file *m, void *p)
@@ -188,8 +178,10 @@ static void stat_seq_stop(struct seq_file *m, void *p)
 
 static int stat_seq_show(struct seq_file *s, void *v)
 {
-	struct trace_stat_list *l = list_entry(v, struct trace_stat_list, list);
-	return current_tracer.stat_show(s, l->stat);
+	struct trace_stat_list *entry =
+		list_entry(v, struct trace_stat_list, list);
+
+	return current_tracer.stat_show(s, entry->stat);
 }
 
 static const struct seq_operations trace_stat_seq_ops = {
@@ -237,7 +229,6 @@ static int __init tracing_stat_init(void)
 	struct dentry *d_tracing;
 	struct dentry *entry;
 
-	INIT_LIST_HEAD(&stat_list.list);
 	d_tracing = tracing_init_dentry();
 
 	entry = debugfs_create_file("trace_stat", 0444, d_tracing,