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