linux-kernel - Re: [PATCH] arch: um: kernel: skas: mmu: remove pmd_free() and pud_free() for failure processing in init_stub

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Message-ID: <5285838C.6070508@asianux.com>
Date:	Fri, 15 Nov 2013 10:14:36 +0800
From:	Chen Gang <gang.chen@...anux.com>
To:	Hugh Dickins <hughd@...gle.com>
CC:	Jeff Dike <jdike@...toit.com>, Richard Weinberger <richard@....at>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	uml-devel <user-mode-linux-devel@...ts.sourceforge.net>,
	uml-user <user-mode-linux-user@...ts.sourceforge.net>
Subject: Re: [PATCH] arch: um: kernel: skas: mmu: remove pmd_free() and pud_free()
 for failure processing in init_stub_pte()

On 11/14/2013 03:33 PM, Chen Gang wrote:
> On 11/14/2013 02:48 PM, Chen Gang wrote:
>>> >From the look of it, if an error did occur in init_stub_pte(),
>>>> then the special mapping of STUB_CODE and STUB_DATA would not
>>>> be installed, so this area would be invisible to munmap and exit,
>>>> and with your patch then the pages allocated likely to be leaked.
>>>>
>> It sounds reasonable to me: "although 'pgd' related with 'mm', but they
>> are not installed". But just like you said originally: "better get ACK
>> from some mm guys".
>>
>>
>> Hmm... is it another issue: "after STUB_CODE succeeds, but STUB_DATA
>> fails, the STUB_CODE will be leaked".
>>
>>
>>>> Which is not to say that the existing code is actually correct:
>>>> you're probably right that it's technically wrong.  But it would
>>>> be very hard to get init_stub_pte() to fail, and has anyone
>>>> reported a problem with it?  My guess is not, and my own
>>>> inclination to dabble here is zero.
>>>>
>> Yeah.
>>
> 
> If we can not get ACK from any mm guys, and we have no enough time
> resource to read related source code, for me, I still recommend to
> remove p?d_free() in failure processing.
> 

Oh, I am very sorry to Hugh and Richard, I make a mistake in common
sense: I recognized incorrect members (I treated Hugh as Richard), Hugh
is "mm guys".

Next time, I should see the mail carefully, not only for contents, but
also for senders.

Sorry again to both of you.

Thanks.

> In the worst cases, we will leak a little memory, and no any other
> negative effect, it is an executable way which is no any risks.
> 
> For current mm implementation, it seems we can not assume any thing,
> although they sounds (or should be) reasonable (include what you said
> about mm).
> 
> 
> Thanks.
> 


-- 
Chen Gang
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