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[dm-devel] 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.  


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).

  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.

agk redhat com

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