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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 | } |