| David Howells | 6cc88bc | 2008-11-14 10:39:21 +1100 | [diff] [blame] | 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 | } |