lib/is_single_threaded.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /* Function to determine if a thread group is single threaded or not
   3  *
   4  * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
   5  * Written by David Howells (dhowells@redhat.com)
   6  * - Derived from security/selinux/hooks.c
   7  */
   8 #include <linux/sched/signal.h>
   9 #include <linux/sched/task.h>
  10 #include <linux/sched/mm.h>
  11
  12 /*
  13  * Returns true if the task does not share ->mm with another thread/process.
  14  */
  15 bool current_is_single_threaded(void)
  16 {
  17         struct task_struct *task = current;
  18         struct mm_struct *mm = task->mm;
  19         struct task_struct *p, *t;
  20         bool ret;
  21
  22         if (atomic_read(&task->signal->live) != 1)
  23                 return false;
  24
  25         if (atomic_read(&mm->mm_users) == 1)
  26                 return true;
  27
  28         ret = false;
  29         rcu_read_lock();
  30         for_each_process(p) {
  31                 if (unlikely(p->flags & PF_KTHREAD))
  32                         continue;
  33                 if (unlikely(p == task->group_leader))
  34                         continue;
  35
  36                 for_each_thread(p, t) {
  37                         if (unlikely(t->mm == mm))
  38                                 goto found;
  39                         if (likely(t->mm))
  40                                 break;
  41                         /*
  42                          * t->mm == NULL. Make sure next_thread/next_task
  43                          * will see other CLONE_VM tasks which might be
  44                          * forked before exiting.
  45                          */
  46                         smp_rmb();
  47                 }
  48         }
  49         ret = true;
  50 found:
  51         rcu_read_unlock();
  52
  53         return ret;
  54 }