Branch data     Line data    Source code

       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                 :          0 : bool current_is_single_threaded(void)
      19                 :            : {
      20                 :          0 :         struct task_struct *task = current;
      21                 :          0 :         struct mm_struct *mm = task->mm;
      22                 :            :         struct task_struct *p, *t;
      23                 :            :         bool ret;
      24                 :            : 
      25         [ #  # ]:          0 :         if (atomic_read(&task->signal->live) != 1)
      26                 :            :                 return false;
      27                 :            : 
      28         [ #  # ]:          0 :         if (atomic_read(&mm->mm_users) == 1)
      29                 :            :                 return true;
      30                 :            : 
      31                 :            :         ret = false;
      32                 :            :         rcu_read_lock();
      33         [ #  # ]:          0 :         for_each_process(p) {
      34         [ #  # ]:          0 :                 if (unlikely(p->flags & PF_KTHREAD))
      35                 :          0 :                         continue;
      36         [ #  # ]:          0 :                 if (unlikely(p == task->group_leader))
      37                 :          0 :                         continue;
      38                 :            : 
      39                 :            :                 t = p;
      40                 :            :                 do {
      41         [ #  # ]:          0 :                         if (unlikely(t->mm == mm))
      42                 :            :                                 goto found;
      43         [ #  # ]:          0 :                         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                 :          0 :                         smp_rmb();
      51         [ #  # ]:          0 :                 } while_each_thread(p, t);
      52                 :            :         }
      53                 :            :         ret = true;
      54                 :            : found:
      55                 :            :         rcu_read_unlock();
      56                 :            : 
      57                 :          0 :         return ret;
      58                 :            : }