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

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Message-ID: <555896EB.7040002@plexistor.com>
Date:	Sun, 17 May 2015 16:26:03 +0300
From:	Boaz Harrosh <boaz@...xistor.com>
To:	Rik van Riel <riel@...hat.com>, Daniel Phillips <daniel@...nq.net>,
	linux-kernel@...r.kernel.org
CC:	linux-fsdevel@...r.kernel.org, tux3@...3.org,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Subject: Re: [FYI] tux3: Core changes

On 05/14/2015 03:59 PM, Rik van Riel wrote:
> On 05/14/2015 04:26 AM, Daniel Phillips wrote:
>> Hi Rik,
<>
> 
> The issue is that things like ptrace, AIO, infiniband
> RDMA, and other direct memory access subsystems can take
> a reference to page A, which Tux3 clones into a new page B
> when the process writes it.
> 
> However, while the process now points at page B, ptrace,
> AIO, infiniband, etc will still be pointing at page A.
> 

All these problems can also happen with truncate+new-extending-write

It is the responsibility of the application to take file/range locks
to prevent these page-pinned problems.

> This causes the process and the other subsystem to each
> look at a different page, instead of at shared state,
> causing ptrace to do nothing, AIO and RDMA data to be
> invisible (or corrupted), etc...
> 

Again these problems already exist. Consider each in-place-write
being a truncate (punch hole) + new-write is that not the same?

Cheers
Boaz

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