Root/lib/is_single_threaded.c

1/* Function to determine if a thread group is single threaded or not
2 *
3 * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
4 * Written by David Howells (dhowells@redhat.com)
5 * - Derived from security/selinux/hooks.c
6 *
7 * This program is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU General Public Licence
9 * as published by the Free Software Foundation; either version
10 * 2 of the Licence, or (at your option) any later version.
11 */
12
13#include <linux/sched.h>
14
15/*
16 * Returns true if the task does not share ->mm with another thread/process.
17 */
18bool current_is_single_threaded(void)
19{
20    struct task_struct *task = current;
21    struct mm_struct *mm = task->mm;
22    struct task_struct *p, *t;
23    bool ret;
24
25    if (atomic_read(&task->signal->live) != 1)
26        return false;
27
28    if (atomic_read(&mm->mm_users) == 1)
29        return true;
30
31    ret = false;
32    rcu_read_lock();
33    for_each_process(p) {
34        if (unlikely(p->flags & PF_KTHREAD))
35            continue;
36        if (unlikely(p == task->group_leader))
37            continue;
38
39        t = p;
40        do {
41            if (unlikely(t->mm == mm))
42                goto found;
43            if (likely(t->mm))
44                break;
45            /*
46             * t->mm == NULL. Make sure next_thread/next_task
47             * will see other CLONE_VM tasks which might be
48             * forked before exiting.
49             */
50            smp_rmb();
51        } while_each_thread(p, t);
52    }
53    ret = true;
54found:
55    rcu_read_unlock();
56
57    return ret;
58}
59

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