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    SubjectRe: hibernation/snapshot design [was Re: [PATCH] Remove process freezer from suspend to RAM pathway]
    Hi!

    > > Freezer is not needed for snapshot -- it is needed so that we can
    > > write out the snapshot to disk without the need for special
    > > drivers/block/simple-ide-for-suspend.c. (We are doing snapshot, then
    > > write to disk from userland code in uswsusp).
    >
    > Yes.
    >
    > BTW, this patch:
    >
    > http://www.sisk.pl/kernel/hibernation_and_suspend/2.6.22-rc7/patches/15-freezer-make-kernel-threads-nonfreezable-by-default.patch
    >
    > that's queued up in -mm contains a freezer documentation update, in which the
    > reasons of using it, as well as its limitations, are described.
    >
    > To summarize what was previously said in this thread:
    >
    > * Apparently, we agree that the freezer is _generally_ not needed for suspend
    > (ie. any transition to a system sleep state other than hibernation), but some
    > of us (eg. me) think that it wouldn't be reasonable to drop the freezer from
    > the suspend code path _right_ _now_ .
    >
    > * Some of us, including you, Nigel and me, think that the freezer is needed
    > for hibernation (please see the document in the patch above for details).
    > In the (very) long run this might be avoided too, but (IMO) certainly not at
    > this point.
    >
    > * We seem to agree that in order to remove the freezer from the suspend code
    > path some work needs to be done on device drivers, driver midlayers and the
    > PM core. We also need to do some work on the PM core in order to introduce
    > a separate hibernation framework and IMO it would be reasonable to
    > synchronize these efforts.
    >
    > * We are now to decide what to do so that the freezer can be safely removed
    > from the suspend code path and how to integrate that change with the
    > hibernation code path (if possible and reasonable).

    Nice summary, thanks.

    > * The freezer vs FUSE issue that started this thread remains unresolved, so
    > it would be desirable to provide a short-term fix (need not be very nice).

    Actually there are _2_ freezer vs FUSE issues, and one of them should
    be simple to solve, once we have sysrq-t of the deadlock. (Or did I
    miss it somewhere with discussion going on 10 lists in parallel?)
    Pavel
    --
    (english) http://www.livejournal.com/~pavelmachek
    (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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