Merge branch 'x86-topology-for-linus' of git://git.kernel.org/pub/scm/linux/kernel...
[platform/kernel/linux-starfive.git] / lib / is_single_threaded.c
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 }