linux/lib/is_single_threaded.c
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   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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