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1// SPDX-License-Identifier: GPL-2.0-or-later2/* Function to determine if a thread group is single threaded or not3 *4 * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.5 * Written by David Howells (dhowells@redhat.com)6 * - Derived from security/selinux/hooks.c7 */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_task43 * will see other CLONE_VM tasks which might be44 * forked before exiting.45 */46 smp_rmb();47 }48 }49 ret = true;50found:51 rcu_read_unlock();52 53 return ret;54}55