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Linux/lib/is_single_threaded.c

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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 #include <linux/sched/signal.h>
 13 #include <linux/sched/task.h>
 14 #include <linux/sched/mm.h>
 15 
 16 /*
 17  * Returns true if the task does not share ->mm with another thread/process.
 18  */
 19 bool current_is_single_threaded(void)
 20 {
 21         struct task_struct *task = current;
 22         struct mm_struct *mm = task->mm;
 23         struct task_struct *p, *t;
 24         bool ret;
 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         rcu_read_lock();
 34         for_each_process(p) {
 35                 if (unlikely(p->flags & PF_KTHREAD))
 36                         continue;
 37                 if (unlikely(p == task->group_leader))
 38                         continue;
 39 
 40                 for_each_thread(p, t) {
 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                 }
 52         }
 53         ret = true;
 54 found:
 55         rcu_read_unlock();
 56 
 57         return ret;
 58 }
 59 

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