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  * is_single_threaded - Determine if a thread group is single-threaded or not
  17  * @p: A task in the thread group in question
  18  *
  19  * This returns true if the thread group to which a task belongs is single
  20  * threaded, false if it is not.
  21  */
  22 bool is_single_threaded(struct task_struct *p)
  23 {
  24         struct task_struct *g, *t;
  25         struct mm_struct *mm = p->mm;
  26
  27         if (atomic_read(&p->signal->count) != 1)
  28                 goto no;
  29
  30         if (atomic_read(&p->mm->mm_users) != 1) {
  31                 read_lock(&tasklist_lock);
  32                 do_each_thread(g, t) {
  33                         if (t->mm == mm && t != p)
  34                                 goto no_unlock;
  35                 } while_each_thread(g, t);
  36                 read_unlock(&tasklist_lock);
  37         }
  38
  39         return true;
  40
  41 no_unlock:
  42         read_unlock(&tasklist_lock);
  43 no:
  44         return false;
  45 }