/* Function to determine if a thread group is single threaded or not
   *
   * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
   * Written by David Howells (dhowells@redhat.com)
   * - Derived from security/selinux/hooks.c
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public Licence
   * as published by the Free Software Foundation; either version
   * 2 of the Licence, or (at your option) any later version.
   */
  
  #include <linux/sched.h>
  
  /**
   * is_single_threaded - Determine if a thread group is single-threaded or not
   * @p: A task in the thread group in question
   *
   * This returns true if the thread group to which a task belongs is single
   * threaded, false if it is not.
   */
  bool is_single_threaded(struct task_struct *p)
  {
  	struct task_struct *g, *t;
  	struct mm_struct *mm = p->mm;
  
  	if (atomic_read(&p->signal->count) != 1)
  		goto no;
  
  	if (atomic_read(&p->mm->mm_users) != 1) {
  		read_lock(&tasklist_lock);
  		do_each_thread(g, t) {
  			if (t->mm == mm && t != p)
  				goto no_unlock;
  		} while_each_thread(g, t);
  		read_unlock(&tasklist_lock);
  	}
  
  	return true;
  
  no_unlock:
  	read_unlock(&tasklist_lock);
  no:
  	return false;
  }