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

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Message-ID: <20061108023039.GF30653@agk.surrey.redhat.com>
Date:	Wed, 8 Nov 2006 02:30:39 +0000
From:	Alasdair G Kergon <agk@...hat.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
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>
Subject: Re: [PATCH 2.6.19 5/5] fs: freeze_bdev with semaphore not mutex

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).

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

Maybe: don't allow freeze_filesystems() to run when the system is in that
state; or, use device-mapper suspend instead of freeze_bdev directly where
dm is involved; or skip dm devices that are already frozen - all with
appropriate dependency tracking to process devices in the right order.

Alasdair
-- 
agk@...hat.com
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