linux-kernel - Re: [PATCH 2.6.19 5/5] fs: freeze

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Date:	Wed, 8 Nov 2006 13:10:18 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alasdair G Kergon <agk@...hat.com>
Cc:	Eric Sandeen <sandeen@...hat.com>, Andrew Morton <akpm@...l.org>,
	linux-kernel@...r.kernel.org, dm-devel@...hat.com,
	Srinivasa DS <srinivasa@...ibm.com>,
	Nigel Cunningham <nigel@...pend2.net>
Subject: Re: [PATCH 2.6.19 5/5] fs: freeze_bdev with semaphore not mutex

On Wednesday, 8 November 2006 03:30, Alasdair G Kergon wrote:
> On Tue, Nov 07, 2006 at 11:49:51PM +0000, Alasdair G Kergon wrote:
> > I hadn't noticed that -mm patch.  I'll take a look.  
> 
> swsusp-freeze-filesystems-during-suspend-rev-2.patch
> 
> I think you need to give more thought to device-mapper
> interactions here.  If an underlying device is suspended
> by device-mapper without freezing the filesystem (the
> normal state) and you issue a freeze_bdev on a device
> above it, the freeze_bdev may never return if it attempts
> any synchronous I/O (as it should).

Well, it looks like the interactions with dm add quite a bit of
complexity here.

> Try:
>   while process generating I/O to filesystem on LVM
>   issue dmsetup suspend --nolockfs (which the lvm2 tools often do)
>   try your freeze_filesystems()

Okay, I will.

> Maybe: don't allow freeze_filesystems() to run when the system is in that
> state;

I'd like to avoid that (we may be running out of battery power at this point).

> or, use device-mapper suspend instead of freeze_bdev directly where 
> dm is involved;

How do I check if dm is involved?

> or skip dm devices that are already frozen - all with 
> appropriate dependency tracking to process devices in the right order.

I'd prefer this one, but probably the previous one is simpler to start with.

Greetings,
Rafael


-- 
You never change things by fighting the existing reality.
		R. Buckminster Fuller
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