/* 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> /* * 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;}