1// SPDX-License-Identifier: GPL-2.0-or-later
2/* Function to determine if a thread group is single threaded or not
3 *
4 * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
5 * Written by David Howells (dhowells@redhat.com)
6 * - Derived from security/selinux/hooks.c
7 */
8#include <linux/sched/signal.h>
9#include <linux/sched/task.h>
10#include <linux/sched/mm.h>
11
12/*
13 * Returns true if the task does not share ->mm with another thread/process.
14 */
15bool current_is_single_threaded(void)
16{
17	struct task_struct *task = current;
18	struct mm_struct *mm = task->mm;
19	struct task_struct *p, *t;
20	bool ret;
21
22	if (atomic_read(&task->signal->live) != 1)
23		return false;
24
25	if (atomic_read(&mm->mm_users) == 1)
26		return true;
27
28	ret = false;
29	rcu_read_lock();
30	for_each_process(p) {
31		if (unlikely(p->flags & PF_KTHREAD))
32			continue;
33		if (unlikely(p == task->group_leader))
34			continue;
35
36		for_each_thread(p, t) {
37			if (unlikely(t->mm == mm))
38				goto found;
39			if (likely(t->mm))
40				break;
41			/*
42			 * t->mm == NULL. Make sure next_thread/next_task
43			 * will see other CLONE_VM tasks which might be
44			 * forked before exiting.
45			 */
46			smp_rmb();
47		}
48	}
49	ret = true;
50found:
51	rcu_read_unlock();
52
53	return ret;
54}
55