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

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Date:	Sat, 5 May 2012 11:29:03 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	mtk.manpages@...il.com
Cc:	Nick Piggin <npiggin@...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

> 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?

>
> [[
> 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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