mirror of
https://github.com/AuxXxilium/linux_dsm_epyc7002.git
synced 2024-11-25 05:30:54 +07:00
967cc53711
is_current_single_threaded() can safely miss a freshly forked CLONE_VM task, but in this case it must not miss its parent. That is why we take mm->mmap_sem for writing to make sure a thread/task with the same ->mm can't pass exit_mm() and disappear. However we can avoid ->mmap_sem and rely on rcu/barriers: - if we do not see the exiting parent on thread/process list we see the result of list_del_rcu(), in this case we must also see the result of list_add_rcu() which does wmb(). - if we do see the parent but its ->mm == NULL, we need rmb() to make sure we can't miss the child. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Acked-by: David Howells <dhowells@redhat.com> Signed-off-by: James Morris <jmorris@namei.org>
59 lines
1.3 KiB
C
59 lines
1.3 KiB
C
/* 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;
|
|
}
|