1 /* Function to determine if a thread group is single threaded or not 2 * 3 * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved. 4 * Written by David Howells (dhowells@redhat.com) 5 * - Derived from security/selinux/hooks.c 6 * 7 * This program is free software; you can redistribute it and/or 8 * modify it under the terms of the GNU General Public Licence 9 * as published by the Free Software Foundation; either version 10 * 2 of the Licence, or (at your option) any later version. 11 */ 12 #include <linux/sched/signal.h> 13 14 /* 15 * Returns true if the task does not share ->mm with another thread/process. 16 */ 17 bool current_is_single_threaded(void) 18 { 19 struct task_struct *task = current; 20 struct mm_struct *mm = task->mm; 21 struct task_struct *p, *t; 22 bool ret; 23 24 if (atomic_read(&task->signal->live) != 1) 25 return false; 26 27 if (atomic_read(&mm->mm_users) == 1) 28 return true; 29 30 ret = false; 31 rcu_read_lock(); 32 for_each_process(p) { 33 if (unlikely(p->flags & PF_KTHREAD)) 34 continue; 35 if (unlikely(p == task->group_leader)) 36 continue; 37 38 for_each_thread(p, t) { 39 if (unlikely(t->mm == mm)) 40 goto found; 41 if (likely(t->mm)) 42 break; 43 /* 44 * t->mm == NULL. Make sure next_thread/next_task 45 * will see other CLONE_VM tasks which might be 46 * forked before exiting. 47 */ 48 smp_rmb(); 49 } 50 } 51 ret = true; 52 found: 53 rcu_read_unlock(); 54 55 return ret; 56 } 57