Message-ID: <555D500B.4080901@phunq.net>
Date: Wed, 20 May 2015 20:24:59 -0700
From: Daniel Phillips <daniel@phunq.net>
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To: Rik van Riel <riel@redhat.com>, Jan Kara <jack@suse.cz>,
        David Lang <david@lang.hm>
CC: linux-fsdevel@vger.kernel.org, tux3@tux3.org, linux-kernel@vger.kernel.org,
        OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Subject: Re: [FYI] tux3: Core changes
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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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