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 13 #include <linux/sched.h> 14 15 /* 16 * Returns true if the task does not share ->mm with another thread/process. 17 */ current_is_single_threaded(void)18bool current_is_single_threaded(void) 19 { 20 struct task_struct *task = current; 21 struct mm_struct *mm = task->mm; 22 struct task_struct *p, *t; 23 bool ret; 24 25 if (atomic_read(&task->signal->live) != 1) 26 return false; 27 28 if (atomic_read(&mm->mm_users) == 1) 29 return true; 30 31 ret = false; 32 rcu_read_lock(); 33 for_each_process(p) { 34 if (unlikely(p->flags & PF_KTHREAD)) 35 continue; 36 if (unlikely(p == task->group_leader)) 37 continue; 38 39 t = p; 40 do { 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 } while_each_thread(p, t); 52 } 53 ret = true; 54 found: 55 rcu_read_unlock(); 56 57 return ret; 58 } 59