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

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Message-ID: <555D500B.4080901@phunq.net>
Date:	Wed, 20 May 2015 20:24:59 -0700
From:	Daniel Phillips <daniel@...nq.net>
To:	Rik van Riel <riel@...hat.com>, Jan Kara <jack@...e.cz>,
	David Lang <david@...g.hm>
CC:	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 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.

Regards,

Daniel
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