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    SubjectRe: Hibernation considerations
    On Tue, 17 Jul 2007, Jeremy Maitin-Shepard wrote:

    > writes:
    > [snip]
    >>> How do you guarantee that no tasks are scheduled when you get back to the
    >>> hibernated kernel?
    >> just don't schedule any userspace tasks. all you need to do is to execute the
    >> ACPI sleep functions. you normally do that after stopping userspace
    >> anyway.
    > What does "stopping userspace" mean? You already said it does not mean
    > disabling interrupts. But using the freezer is also not an option,
    > since the avoidance of that is the main reason for the kexec approach in
    > the first place.

    just don't schedule any non-kernel threads.

    remember that the normal shutdown/suspend procedure is (from another
    related thread)

    > >>sys_reboot(LINUX_REBOOT_CMD_KEXEC)
    > >> kernel_kexec
    > >> kernel_restart_prepare
    > >> device_shutdown
    > >> machine_shutdown
    > >> machine_kexec

    I'm just saying that instead of going back to the normal operation of the
    kernel you just go directly to the new shutdown routine instead.

    > [snip]
    >>> Well, not exactly. If your battery runs out of power while you're suspended,
    >>> but you have the image saved, it's still better to restore from the image,
    >> even
    >>> if something may not work correctly after the restore, than to risk a loss of
    >>> data.
    >> if things don't work correctly you are still risking the loss of data, the user
    >> just doesn't know it.
    > It should be possible on any system to do a hibernate followed by a
    > shutdown (and then resume properly, without any problems). Thus, for
    > handling suspend to both, you resume as if the system had been shutdown,
    > rather than resuming as if the system came from S4.

    I agree with this, but according to Rafael if the "hibernated" image is
    assuming that the devices were put into low-power mode by ACPI and you
    boot up instead the system doesn't work right.

    David Lang
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