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    SubjectRe: [dm-devel] Re: [PATCH 3/3] Add timeout feature
    On Thu, Jul 03, 2008 at 09:11:05PM +0900, Takashi Sato wrote:
    > If the freezer accesses the frozen filesystem and causes a deadlock,
    > the above ideas can't solve it

    But you could also say that if the 'freezer' process accesses the frozen
    filesystem and deadlocks then that's just a bug and that userspace code
    should be fixed and there's no need to introduce the complexity of a
    timeout parameter.

    > >Similarly if a device-mapper device is involved, how should the following
    > >sequence behave - A, B or C?
    > >
    > >1. dmsetup suspend (freezes)
    > >2. FIFREEZE
    > >3. FITHAW
    > >4. dmsetup resume (thaws)
    > [...]
    > >C:
    > > 1 succeeds, freezes
    > > 2 fails, remains frozen
    > > 3 fails (because device-mapper owns the freeze/thaw), remains frozen
    > > 4 succeeds, thaws
    > I think C is appropriate and the following change makes it possible.
    > How do you think?

    The point I'm trying to make here is:
    Under what real-world circumstances might multiple concurrent freezing
    attempts occur, and which of A, B or C (or other variations) would be
    the most appropriate way of handling such situations?

    A common example is people running xfs_freeze followed by an lvm command
    which also attempts to freeze the filesystem.

    I can see a case for B or C, but personally I prefer A:

    > > 1 succeeds, freezes
    > > 2 succeeds, remains frozen
    > > 3 succeeds, remains frozen
    > > 4 succeeds, thaws


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