GNU Linux-libre 4.19.211-gnu1
[releases.git] / lib / is_single_threaded.c
1 /* Function to determine if a thread group is single threaded or not
2  *
3  * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
4  * Written by David Howells (dhowells@redhat.com)
5  * - Derived from security/selinux/hooks.c
6  *
7  * This program is free software; you can redistribute it and/or
8  * modify it under the terms of the GNU General Public Licence
9  * as published by the Free Software Foundation; either version
10  * 2 of the Licence, or (at your option) any later version.
11  */
12 #include <linux/sched/signal.h>
13 #include <linux/sched/task.h>
14 #include <linux/sched/mm.h>
15
16 /*
17  * Returns true if the task does not share ->mm with another thread/process.
18  */
19 bool current_is_single_threaded(void)
20 {
21         struct task_struct *task = current;
22         struct mm_struct *mm = task->mm;
23         struct task_struct *p, *t;
24         bool ret;
25
26         if (atomic_read(&task->signal->live) != 1)
27                 return false;
28
29         if (atomic_read(&mm->mm_users) == 1)
30                 return true;
31
32         ret = false;
33         rcu_read_lock();
34         for_each_process(p) {
35                 if (unlikely(p->flags & PF_KTHREAD))
36                         continue;
37                 if (unlikely(p == task->group_leader))
38                         continue;
39
40                 for_each_thread(p, t) {
41                         if (unlikely(t->mm == mm))
42                                 goto found;
43                         if (likely(t->mm))
44                                 break;
45                         /*
46                          * t->mm == NULL. Make sure next_thread/next_task
47                          * will see other CLONE_VM tasks which might be
48                          * forked before exiting.
49                          */
50                         smp_rmb();
51                 }
52         }
53         ret = true;
54 found:
55         rcu_read_unlock();
56
57         return ret;
58 }