linux-kernel - Re: mlock: mlocked pages are unevictable

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Date:	Wed, 22 Oct 2008 02:18:26 +0900
From:	"KOSAKI Motohiro" <kosaki.motohiro@...fujitsu.com>
To:	"Heiko Carstens" <heiko.carstens@...ibm.com>
Cc:	"Nick Piggin" <npiggin@...e.de>, linux-kernel@...r.kernel.org,
	"Hugh Dickins" <hugh@...itas.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Rik van Riel" <riel@...hat.com>,
	"Lee Schermerhorn" <lee.schermerhorn@...com>, linux-mm@...ck.org
Subject: Re: mlock: mlocked pages are unevictable

2008/10/22 KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>:
> Hi
>
>> I think the following part of your patch:
>>
>>> diff --git a/mm/swap.c b/mm/swap.c
>>> index fee6b97..bc58c13 100644
>>> --- a/mm/swap.c
>>> +++ b/mm/swap.c
>>> @@ -278,7 +278,7 @@ void lru_add_drain(void)
>>>       put_cpu();
>>>  }
>>>
>>> -#ifdef CONFIG_NUMA
>>> +#if defined(CONFIG_NUMA) || defined(CONFIG_UNEVICTABLE_LRU)
>>>  static void lru_add_drain_per_cpu(struct work_struct *dummy)
>>>  {
>>>       lru_add_drain();
>>
>> causes this (allyesconfig on s390):
>
> hm,
>
> I don't think so.
>
> Actually, this patch has
>   mmap_sem -> lru_add_drain_all() dependency.
>
> but its dependency already exist in another place.
> example,
>
>  sys_move_pages()
>      do_move_pages()  <- down_read(mmap_sem)
>          migrate_prep()
>               lru_add_drain_all()
>
> Thought?

ok. maybe I understand this issue.

This bug is caused by folloing dependencys.

some VM place has
      mmap_sem -> kevent_wq

net/core/dev.c::dev_ioctl()  has
     rtnl_lock  ->  mmap_sem        (*) almost ioctl has
copy_from_user() and it cause page fault.

linkwatch_event has
    kevent_wq -> rtnl_lock


So, I think VM subsystem shouldn't use kevent_wq because many driver
use ioctl and work queue combination.
then drivers fixing isn't easy.

I'll make the patch soon.
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