Project import
diff --git a/lib/is_single_threaded.c b/lib/is_single_threaded.c
new file mode 100644
index 0000000..bd2bea9
--- /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;
+}
