Subject: Re: [PATCH -mm 0/2] Use freezeable workqueues to avoid
	suspend-related XFS corruptions
From: Nigel Cunningham <nigel@suspend2.net>
Reply-To: nigel@suspend2.net
To: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: David Chinner <dgc@sgi.com>, Andrew Morton <akpm@osdl.org>,
       LKML <linux-kernel@vger.kernel.org>, Pavel Machek <pavel@ucw.cz>
In-Reply-To: <200611202318.29207.rjw@sisk.pl>
References: <200611160912.51226.rjw@sisk.pl>
	 <200611202140.47322.rjw@sisk.pl>
	 <1164060206.14889.13.camel@nigel.suspend2.net>
	 <200611202318.29207.rjw@sisk.pl>
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Date: Tue, 21 Nov 2006 09:26:26 +1100
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Hi.

On Mon, 2006-11-20 at 23:18 +0100, Rafael J. Wysocki wrote:
> I think I/O can only be submitted from the process context.  Thus if we freeze
> all (and I mean _all_) threads that are used by filesystems, including worker
> threads, we should effectively prevent fs-related I/O from being submitted
> after tasks have been frozen.

I know that will work. It's what I used to do before the switch to bdev
freezing. I guess I need to look again at why I made the switch. Perhaps
it was just because you guys gave freezing kthreads a bad wrap as too
invasive or something. Bdev freezing is certainly fewer lines of code.

> This can be done with the help of create_freezeable_workqueue() introduced in
> this patch and I'd like to implement it (and there are only a few filesystems
> that use work queues).
> 
> The freezing of bdevs might be a good solution if:
> (1) we were sure it wouldn't interact with dm in a wrong way,
> (2) _all_ of the filesystems implemented it.
> For now, neither (1) nor (2) are satisfied and we need to know we're safe
> _now_.

Yeah.

Regards,

Nigel

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