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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  */
  18 bool 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         might_sleep();
  26
  27         if (atomic_read(&task->signal->live) != 1)
  28                 return false;
  29
  30         if (atomic_read(&mm->mm_users) == 1)
  31                 return true;
  32
  33         ret = false;
  34         down_write(&mm->mmap_sem);
  35         rcu_read_lock();
  36         for_each_process(p) {
  37                 if (unlikely(p->flags & PF_KTHREAD))
  38                         continue;
  39                 if (unlikely(p == task->group_leader))
  40                         continue;
  41
  42                 t = p;
  43                 do {
  44                         if (unlikely(t->mm == mm))
  45                                 goto found;
  46                         if (likely(t->mm))
  47                                 break;
  48                 } while_each_thread(p, t);
  49         }
  50         ret = true;
  51 found:
  52         rcu_read_unlock();
  53         up_write(&mm->mmap_sem);
  54
  55         return ret;
  56 }