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
13 #include <linux/sched.h>
14
15 /**
16 * is_single_threaded - Determine if a thread group is single-threaded or not
17 * @p: A task in the thread group in question
18 *
19 * This returns true if the thread group to which a task belongs is single
20 * threaded, false if it is not.
21 */
22 bool is_single_threaded(struct task_struct *p)
23 {
24 struct task_struct *g, *t;
25 struct mm_struct *mm = p->mm;
26
27 if (atomic_read(&p->signal->count) != 1)
28 goto no;
29
30 if (atomic_read(&p->mm->mm_users) != 1) {
31 read_lock(&tasklist_lock);
32 do_each_thread(g, t) {
33 if (t->mm == mm && t != p)
34 goto no_unlock;
35 } while_each_thread(g, t);
36 read_unlock(&tasklist_lock);
37 }
38
39 return true;
40
41 no_unlock:
42 read_unlock(&tasklist_lock);
43 no:
44 return false;
45 }
46
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