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

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Date:	Sun, 17 May 2015 22:20:58 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Boaz Harrosh <boaz@...xistor.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 05/17/2015 09:26 AM, Boaz Harrosh wrote:
> 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.

It is unreasonable to expect a process that is being ptraced
(potentially without its knowledge) to take special measures
to protect the ptraced memory from disappearing.

It is impossible for the debugger to take those special measures
for anonymous memory, or unlinked inodes.

I don't think your requirement is workable or reasonable.

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