From mboxrd@z Thu Jan  1 00:00:00 1970
From: Daniel Phillips <daniel@phunq.net>
Subject: Re: [FYI] tux3: Core changes
Date: Wed, 20 May 2015 20:24:59 -0700
Message-ID: <555D500B.4080901@phunq.net>
References: <8f886f13-6550-4322-95be-93244ae61045@phunq.net>
 <55545C2F.8040207@phunq.net> <20150519140045.GA16313@quack.suse.cz>
 <555B8C79.4090909@phunq.net>
 <alpine.DEB.2.02.1505191327310.25387@nftneq.ynat.uz>
 <20150520144429.GA17783@quack.suse.cz> <555CB4B6.8050305@phunq.net>
 <555CE62C.5030202@redhat.com> <555D0FDF.3070303@phunq.net>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Cc: linux-fsdevel@vger.kernel.org, tux3@tux3.org, linux-kernel@vger.kernel.org,
 OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
To: Rik van Riel <riel@redhat.com>, Jan Kara <jack@suse.cz>,
 David Lang <david@lang.hm>
Return-path: <tux3-bounces@phunq.net>
In-Reply-To: <555D0FDF.3070303@phunq.net>
List-Unsubscribe: <http://phunq.net/mailman/options/tux3>,
 <mailto:tux3-request@phunq.net?subject=unsubscribe>
List-Archive: <http://phunq.net/pipermail/tux3/>
List-Post: <mailto:tux3@phunq.net>
List-Help: <mailto:tux3-request@phunq.net?subject=help>
List-Subscribe: <http://phunq.net/mailman/listinfo/tux3>,
 <mailto:tux3-request@phunq.net?subject=subscribe>
Errors-To: tux3-bounces@phunq.net
Sender: "Tux3" <tux3-bounces@phunq.net>
List-Id: linux-fsdevel.vger.kernel.org

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