kernel: fix is_single_threaded
[linux-2.6.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
13 #include <linux/sched.h>
14
15 /*
16  * Returns true if the task does not share ->mm with another thread/process.
17  */
18 bool is_single_threaded(struct task_struct *task)
19 {
20         struct mm_struct *mm = task->mm;
21         struct task_struct *p, *t;
22         bool ret;
23
24         might_sleep();
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         down_write(&mm->mmap_sem);
34         rcu_read_lock();
35         for_each_process(p) {
36                 if (unlikely(p->flags & PF_KTHREAD))
37                         continue;
38                 if (unlikely(p == task->group_leader))
39                         continue;
40
41                 t = p;
42                 do {
43                         if (unlikely(t->mm == mm))
44                                 goto found;
45                         if (likely(t->mm))
46                                 break;
47                 } while_each_thread(p, t);
48         }
49         ret = true;
50 found:
51         rcu_read_unlock();
52         up_write(&mm->mmap_sem);
53
54         return ret;
55 }