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/* Function to determine if a thread group is single threaded or not
*
* Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
* - Derived from security/selinux/hooks.c
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public Licence
* as published by the Free Software Foundation; either version
* 2 of the Licence, or (at your option) any later version.
*/

#include <linux/sched.h>

/*
* Returns true if the task does not share ->mm with another thread/process.
*/
bool current_is_single_threaded(void)
{
struct task_struct *task = current;
struct mm_struct *mm = task->mm;
struct task_struct *p, *t;
bool ret;

if (atomic_read(&task->signal->live) != 1)
return false;

if (atomic_read(&mm->mm_users) == 1)
return true;

ret = false;
rcu_read_lock();
for_each_process(p) {
if (unlikely(p->flags & PF_KTHREAD))
continue;
if (unlikely(p == task->group_leader))
continue;

t = p;
do {
if (unlikely(t->mm == mm))
goto found;
if (likely(t->mm))
break;
/*
* t->mm == NULL. Make sure next_thread/next_task
* will see other CLONE_VM tasks which might be
* forked before exiting.
*/
smp_rmb();
} while_each_thread(p, t);
}
ret = true;
found:
rcu_read_unlock();

return ret;
}
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