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