1 files changed, 58 insertions, 0 deletions
diff --git a/lib/is_single_threaded.c b/lib/is_single_threaded.c
new file mode 100644
index 000000000..bd2bea963
--- /dev/null
+++ b/lib/is_single_threaded.c
@@ -0,0 +1,58 @@
+/* Function to determine if a thread group is single threaded or not
+ *
+ * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ * - Derived from security/selinux/hooks.c
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#include <linux/sched.h>
+
+/*
+ * Returns true if the task does not share ->mm with another thread/process.
+ */
+bool current_is_single_threaded(void)
+{
+	struct task_struct *task = current;
+	struct mm_struct *mm = task->mm;
+	struct task_struct *p, *t;
+	bool ret;
+
+	if (atomic_read(&task->signal->live) != 1)
+		return false;
+
+	if (atomic_read(&mm->mm_users) == 1)
+		return true;
+
+	ret = false;
+	rcu_read_lock();
+	for_each_process(p) {
+		if (unlikely(p->flags & PF_KTHREAD))
+			continue;
+		if (unlikely(p == task->group_leader))
+			continue;
+
+		t = p;
+		do {
+			if (unlikely(t->mm == mm))
+				goto found;
+			if (likely(t->mm))
+				break;
+			/*
+			 * t->mm == NULL. Make sure next_thread/next_task
+			 * will see other CLONE_VM tasks which might be
+			 * forked before exiting.
+			 */
+			smp_rmb();
+		} while_each_thread(p, t);
+	}
+	ret = true;
+found:
+	rcu_read_unlock();
+
+	return ret;
+}