// SPDX-License-Identifier: GPL-2.0-or-later
/* 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
 */
#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;
}