is_single_threaded.c

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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 ([email protected])
 * - 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;

        t = p;
        do {
            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();
        } while_each_thread(p, t);
    }
    ret = true;
found:
    rcu_read_unlock();

    return ret;
}