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 #include <linux/sched/task.h> 14 #include <linux/sched/mm.h> 15 16 /* 17 * Returns true if the task does not share ->mm with another thread/process. 18 */ 19 bool current_is_single_threaded(void) 20 { 21 struct task_struct *task = current; 22 struct mm_struct *mm = task->mm; 23 struct task_struct *p, *t; 24 bool ret; 25 26 if (atomic_read(&task->signal->live) != 1) 27 return false; 28 29 if (atomic_read(&mm->mm_users) == 1) 30 return true; 31 32 ret = false; 33 rcu_read_lock(); 34 for_each_process(p) { 35 if (unlikely(p->flags & PF_KTHREAD)) 36 continue; 37 if (unlikely(p == task->group_leader)) 38 continue; 39 40 for_each_thread(p, t) { 41 if (unlikely(t->mm == mm)) 42 goto found; 43 if (likely(t->mm)) 44 break; 45 /* 46 * t->mm == NULL. Make sure next_thread/next_task 47 * will see other CLONE_VM tasks which might be 48 * forked before exiting. 49 */ 50 smp_rmb(); 51 } 52 } 53 ret = true; 54 found: 55 rcu_read_unlock(); 56 57 return ret; 58 } 59