is_single_threaded.c 1.38 KB
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/* 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.
 */
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#include <linux/sched/signal.h>
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#include <linux/sched/task.h>
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#include <linux/sched/mm.h>
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/*
 * Returns true if the task does not share ->mm with another thread/process.
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 */
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bool current_is_single_threaded(void)
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{
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	struct task_struct *task = current;
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	struct mm_struct *mm = task->mm;
	struct task_struct *p, *t;
	bool ret;

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

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		for_each_thread(p, t) {
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			if (unlikely(t->mm == mm))
				goto found;
			if (likely(t->mm))
				break;
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			/*
			 * t->mm == NULL. Make sure next_thread/next_task
			 * will see other CLONE_VM tasks which might be
			 * forked before exiting.
			 */
			smp_rmb();
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		}
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	}
	ret = true;
found:
	rcu_read_unlock();
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	return ret;
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}