ocfs2/dlm: remove potential deadlock -V3
[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / lib / is_single_threaded.c
blobbd2bea963364c757e90db1e47ce557a94d053c0b
1 /* Function to determine if a thread group is single threaded or not
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
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.
13 #include <linux/sched.h>
16 * Returns true if the task does not share ->mm with another thread/process.
18 bool current_is_single_threaded(void)
20 struct task_struct *task = current;
21 struct mm_struct *mm = task->mm;
22 struct task_struct *p, *t;
23 bool ret;
25 if (atomic_read(&task->signal->live) != 1)
26 return false;
28 if (atomic_read(&mm->mm_users) == 1)
29 return true;
31 ret = false;
32 rcu_read_lock();
33 for_each_process(p) {
34 if (unlikely(p->flags & PF_KTHREAD))
35 continue;
36 if (unlikely(p == task->group_leader))
37 continue;
39 t = p;
40 do {
41 if (unlikely(t->mm == mm))
42 goto found;
43 if (likely(t->mm))
44 break;
46 * t->mm == NULL. Make sure next_thread/next_task
47 * will see other CLONE_VM tasks which might be
48 * forked before exiting.
50 smp_rmb();
51 } while_each_thread(p, t);
53 ret = true;
54 found:
55 rcu_read_unlock();
57 return ret;