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    SubjectRe: [PATCH 2.6.19 5/5] fs: freeze_bdev with semaphore not mutex
    Hi!

    > On Fri, Nov 10, 2006 at 12:11:46AM +0100, Pavel Machek wrote:
    > > ? Not sure if I quite understand, but if dm breaks sync... something
    > > is teribly wrong with dm. And we do simple sys_sync()... so I do not
    > > think we have a problem.
    >
    > If you want to handle arbitrary kernel state, you might have a device-mapper
    > device somewhere lower down the stack of devices that is queueing any I/O
    > that reaches it. So anything waiting for I/O completion will wait until
    > the dm process that suspended that device has finished whatever it is doing
    > - and that might be a quick thing carried out by a userspace lvm tool, or
    > a long thing carried out by an administrator using dmsetup.
    >
    > I'm guessing you need a way of detecting such state lower down the stack
    > then optionally either aborting the operation telling the user it can't be
    > done at present; waiting for however long it takes (perhaps for ever if
    > the admin disappeared); or more probably skipping those devices on a
    > 'best endeavours' basis.

    Okay, so you claim that sys_sync can stall, waiting for administator?

    In such case we can simply do one sys_sync() before we start freezing
    userspace... or just more the only sys_sync() there. That way, admin
    has chance to unlock his system.

    Pavel
    --
    (english) http://www.livejournal.com/~pavelmachek
    (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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