Branch data     Line data    Source code

       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                 :          0 : bool current_is_single_threaded(void)
      16                 :            : {
      17                 :          0 :         struct task_struct *task = current;
      18                 :          0 :         struct mm_struct *mm = task->mm;
      19                 :          0 :         struct task_struct *p, *t;
      20                 :          0 :         bool ret;
      21                 :            : 
      22         [ #  # ]:          0 :         if (atomic_read(&task->signal->live) != 1)
      23                 :            :                 return false;
      24                 :            : 
      25         [ #  # ]:          0 :         if (atomic_read(&mm->mm_users) == 1)
      26                 :            :                 return true;
      27                 :            : 
      28                 :          0 :         ret = false;
      29                 :          0 :         rcu_read_lock();
      30         [ #  # ]:          0 :         for_each_process(p) {
      31         [ #  # ]:          0 :                 if (unlikely(p->flags & PF_KTHREAD))
      32                 :          0 :                         continue;
      33         [ #  # ]:          0 :                 if (unlikely(p == task->group_leader))
      34                 :          0 :                         continue;
      35                 :            : 
      36         [ #  # ]:          0 :                 for_each_thread(p, t) {
      37         [ #  # ]:          0 :                         if (unlikely(t->mm == mm))
      38                 :          0 :                                 goto found;
      39         [ #  # ]:          0 :                         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                 :          0 :                         smp_rmb();
      47                 :            :                 }
      48                 :            :         }
      49                 :            :         ret = true;
      50                 :          0 : found:
      51                 :          0 :         rcu_read_unlock();
      52                 :            : 
      53                 :          0 :         return ret;
      54                 :            : }