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 */
15 bool 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;
50 found:
51 rcu_read_unlock();
52
53 return ret;
54 }
55
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