LXR linux/lib/is_single

   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 */
  15bool 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;
  50found:
  51        rcu_read_unlock();
  52
  53        return ret;
  54}
  55