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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 is_single_threaded(struct task_struct *task)
  19 {
  20         struct mm_struct *mm = task->mm;
  21         struct task_struct *p, *t;
  22         bool ret;
  23
  24         might_sleep();
  25
  26         if (atomic_read(&task->signal->live) != 1)
  27                 return false;
  28
  29         if (atomic_read(&mm->mm_users) == 1)
  30                 return true;
  31
  32         ret = false;
  33         down_write(&mm->mmap_sem);
  34         rcu_read_lock();
  35         for_each_process(p) {
  36                 if (unlikely(p->flags & PF_KTHREAD))
  37                         continue;
  38                 if (unlikely(p == task->group_leader))
  39                         continue;
  40
  41                 t = p;
  42                 do {
  43                         if (unlikely(t->mm == mm))
  44                                 goto found;
  45                         if (likely(t->mm))
  46                                 break;
  47                 } while_each_thread(p, t);
  48         }
  49         ret = true;
  50 found:
  51         rcu_read_unlock();
  52         up_write(&mm->mmap_sem);
  53
  54         return ret;
  55 }