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Linux/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                 for_each_thread(p, t) {
 40                         if (unlikely(t->mm == mm))
 41                                 goto found;
 42                         if (likely(t->mm))
 43                                 break;
 44                         /*
 45                          * t->mm == NULL. Make sure next_thread/next_task
 46                          * will see other CLONE_VM tasks which might be
 47                          * forked before exiting.
 48                          */
 49                         smp_rmb();
 50                 }
 51         }
 52         ret = true;
 53 found:
 54         rcu_read_unlock();
 55 
 56         return ret;
 57 }
 58 

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