/* 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/signal.h>

  #include <linux/sched/task.h>

  #include <linux/sched/mm.h>

  /*
   * Returns true if the task does not share ->mm with another thread/process.

   */

  bool current_is_single_threaded(void)

  {

  	struct task_struct *task = current;

  	struct mm_struct *mm = task->mm;
  	struct task_struct *p, *t;
  	bool ret;

  	if (atomic_read(&task->signal->live) != 1)
  		return false;

  	if (atomic_read(&mm->mm_users) == 1)
  		return true;
  
  	ret = false;

  	rcu_read_lock();
  	for_each_process(p) {
  		if (unlikely(p->flags & PF_KTHREAD))
  			continue;
  		if (unlikely(p == task->group_leader))
  			continue;

  		for_each_thread(p, t) {

  			if (unlikely(t->mm == mm))
  				goto found;
  			if (likely(t->mm))
  				break;

  			/*
  			 * t->mm == NULL. Make sure next_thread/next_task
  			 * will see other CLONE_VM tasks which might be
  			 * forked before exiting.
  			 */
  			smp_rmb();

  		}

  	}
  	ret = true;
  found:
  	rcu_read_unlock();

  	return ret;

  }