linux-kernel - Re: [FYI] tux3: Core changes

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Message-ID: <alpine.DEB.2.02.1505202050530.25699@nftneq.ynat.uz>
Date:	Wed, 20 May 2015 20:51:46 -0700 (PDT)
From:	David Lang <david@...g.hm>
To:	Daniel Phillips <daniel@...nq.net>
cc:	Rik van Riel <riel@...hat.com>, Jan Kara <jack@...e.cz>,
	linux-fsdevel@...r.kernel.org, tux3@...3.org,
	linux-kernel@...r.kernel.org,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Subject: Re: [FYI] tux3: Core changes

On Wed, 20 May 2015, Daniel Phillips wrote:

> On 05/20/2015 03:51 PM, Daniel Phillips wrote:
>> On 05/20/2015 12:53 PM, Rik van Riel wrote:
>>> How does tux3 prevent a user of find_get_page() from reading from
>>> or writing into the pre-COW page, instead of the current page?
>>
>> Careful control of the dirty bits (we have two of them, one each
>> for front and back). That is what pagefork_for_blockdirty is about.
>
> Ah, and of course it does not matter if a reader is on the
> pre-cow page. It would be reading the earlier copy, which might
> no longer be the current copy, but it raced with the write so
> nobody should be surprised. That is a race even without page fork.

how do you prevent it from continuing to interact with the old version of the 
page and never see updates or have it's changes reflected on the current page?

David Lang
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