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  */
  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         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;
  54 found:
  55         rcu_read_unlock();
  56
  57         return ret;
  58 }