linux-kernel - Re: [PATCH] Describe race of direct read and fork for unaligned buffers

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Message-ID: <CAPa8GCCh-RrjsQKzh9+Sxx-joRZw4qkpxR9n4svo+QopxAj_XQ@mail.gmail.com>
Date:	Wed, 9 May 2012 09:10:15 +1000
From:	Nick Piggin <npiggin@...il.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
Cc:	mtk.manpages@...il.com, Jan Kara <jack@...e.cz>,
	Jeff Moyer <jmoyer@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, linux-man@...r.kernel.org,
	linux-mm@...ck.org, mgorman@...e.de,
	Andrea Arcangeli <aarcange@...hat.com>,
	Woodman <lwoodman@...hat.com>
Subject: Re: [PATCH] Describe race of direct read and fork for unaligned buffers

On 6 May 2012 01:29, KOSAKI Motohiro <kosaki.motohiro@...il.com> wrote:
>> So, am I correct to assume that right text to add to the page is as below?
>>
>> Nick, can you clarify what you mean by "quiesced"?
>
> finished?

Yes exactly. That might be a simpler word. Thanks!

>
>>
>> [[
>> O_DIRECT IOs should never be run concurrently with fork(2) system call,
>> when the memory buffer is anonymous memory, or comes from mmap(2)
>> with MAP_PRIVATE.
>>
>> Any such IOs, whether submitted with asynchronous IO interface or from
>> another thread in the process, should be quiesced before fork(2) is called.
>> Failure to do so can result in data corruption and undefined behavior in
>> parent and child processes.
>>
>> This restriction does not apply when the memory buffer for the O_DIRECT
>> IOs comes from mmap(2) with MAP_SHARED or from shmat(2).
>> Nor does this restriction apply when the memory buffer has been advised
>> as MADV_DONTFORK with madvise(2), ensuring that it will not be available
>> to the child after fork(2).
>> ]]
>
> I don't have good English and I can't make editorial check. But at least,
> I don't find any technical incorrect explanation here.
>
>  Acked-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
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