[PATCH v9 03/12] scs: add support for stack usage debugging

@@ -184,6 +184,44 @@ int scs_prepare(struct task_struct *tsk, int node)
 	return 0;
 }
 
+#ifdef CONFIG_DEBUG_STACK_USAGE
+static inline unsigned long scs_used(struct task_struct *tsk)
+{
+	unsigned long *p = __scs_base(tsk);
+	unsigned long *end = scs_magic(p);
+	unsigned long s = (unsigned long)p;
+
+	while (p < end && READ_ONCE_NOCHECK(*p))
+		p++;
+
+	return (unsigned long)p - s;
+}
+
+static void scs_check_usage(struct task_struct *tsk)
+{
+	static DEFINE_SPINLOCK(lock);
+	static unsigned long highest;
+	unsigned long used = scs_used(tsk);
+
+	if (used <= highest)
+		return;
+
+	spin_lock(&lock);
+
+	if (used > highest) {
+		pr_info("%s (%d): highest shadow stack usage: %lu bytes\n",
+			tsk->comm, task_pid_nr(tsk), used);
+		highest = used;
+	}
+
+	spin_unlock(&lock);
+}
+#else
+static inline void scs_check_usage(struct task_struct *tsk)
+{
+}
+#endif
+
 bool scs_corrupted(struct task_struct *tsk)
 {
 	unsigned long *magic = scs_magic(__scs_base(tsk));

@@ -200,6 +238,7 @@ void scs_release(struct task_struct *tsk)
 		return;
 
 	WARN_ON(scs_corrupted(tsk));
+	scs_check_usage(tsk);
 
 	scs_account(tsk, -1);
 	task_set_scs(tsk, NULL);