linux-kernel - Re: [PATCH 3/3] Add timeout feature

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Message-ID: <48DCC043.1020207@redhat.com>
Date:	Fri, 26 Sep 2008 06:58:11 -0400
From:	Ric Wheeler <rwheeler@...hat.com>
To:	Takashi Sato <t-sato@...jp.nec.com>
CC:	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...sign.ru>, linux-fsdevel@...r.kernel.org,
	dm-devel@...hat.com, viro@...IV.linux.org.uk,
	linux-ext4@...r.kernel.org, xfs@....sgi.com, axboe@...nel.dk,
	mtk.manpages@...glemail.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] Add timeout feature

Takashi Sato wrote:
> Hi,
>
> Ric Wheeler wrote:
>> Christoph Hellwig wrote:
>>> On Mon, Sep 08, 2008 at 08:53:37PM +0900, Takashi Sato wrote:
>>>
>>>> The timeout feature is added to "freeze ioctl" to solve a deadlock
>>>> when the freezer accesses a frozen filesystem. And new ioctl
>>>> to reset the timeout period is added to extend the timeout period.
>>>> For example, the freezer resets the timeout period to 10 seconds 
>>>> every 5
>>>> seconds.  In this approach, even if the freezer causes a deadlock by
>>>> accessing the frozen filesystem, it will be solved by the timeout
>>>> in 10 seconds and the freezer will be able to recognize that
>>>> at the next reset of timeout period.
>>>>
>>>
>>> And as with all previous posting I still fundamentally disagree about
>>> the need of this functionality.  We don't need a timeout for freezing.
>>
>> I agree with Christoph here, I think that the timeout is unneeded.
>
> I think that your concern is that the freezer cannot recognize the 
> occurrence
> of a timeout and it continues the backup process and the backup data is
> corrupted finally.
> If the freezer can recognize it by the unfreeze ioctl's errono, will 
> your concern
> be solved?
> If so, I will implement it.
>
> Cheers, Takashi
>
I think that is certainly part a big part of my concern.

Also note that the timeout seems to be quite low relative to say the 
standard timeout for a SCSI device (30 seconds worst case).

In general, I am quite supportive of the patch series and think that 
this is a great addition.

Thanks!

Ric


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