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

    On Thursday, 9 November 2006 17:00, Pavel Machek wrote:
    > Hi!
    >
    > > > > Well, it looks like the interactions with dm add quite a bit of
    > > > > complexity here.
    > > >
    > > > What about just fixing xfs (thou shall not write to disk when kernel
    > > > threads are frozen), and getting rid of blockdev freezing?
    > >
    > > Well, first I must admit you were absolutely right being suspicious with
    > > respect to this stuff.
    >
    > (OTOH your patch found real bugs in suspend.c, so...)
    >
    > > OTOH I have no idea _how_ we can tell xfs that the processes have been
    > > frozen. Should we introduce a global flag for that or something?
    >
    > I guess XFS should just do all the writes from process context, and
    > refuse any writing when its threads are frozen... I actually still
    > believe it is doing the right thing, because you can't really write to
    > disk from timer.

    This is from a work queue, so in fact from a process context, but from
    a process that is running with PF_NOFREEZE.

    And I don't think we can forbid filesystems to use work queues. IMO it's
    a legitimate thing to do for an fs.

    _But_.

    Alasdair, do I think correctly that if there's a suspended device-mapper
    device below an non-frozen filesystem, then sys_sync() would block just
    as well as freeze_bdev() on this filesystem?

    Rafael


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