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Re: [PATCH 3/3] Add timeout feature

To: Takashi Sato <t-sato@xxxxxxxxxxxxx>
Subject: Re: [PATCH 3/3] Add timeout feature
From: Ric Wheeler <rwheeler@xxxxxxxxxx>
Date: Fri, 26 Sep 2008 06:58:11 -0400
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Oleg Nesterov <oleg@xxxxxxxxxx>, linux-fsdevel@xxxxxxxxxxxxxxx, dm-devel@xxxxxxxxxx, viro@xxxxxxxxxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, axboe@xxxxxxxxx, mtk.manpages@xxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx
In-reply-to: <D0B0D91F884647D6808626CDFF81E532@xxxxxxxxxxxxxxxx>
References: <20080908205337t-sato@xxxxxxxxxxxxxxx> <20080908171119.GB22521@xxxxxxxxxxxxx> <48DBFD42.6030307@xxxxxxxxxx> <D0B0D91F884647D6808626CDFF81E532@xxxxxxxxxxxxxxxx>
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Takashi Sato wrote:

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.



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