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    SubjectRe: (resend) [PATCH v4 12/12] virtio: balloon: Add freeze, restore handlers to support S4
    On (Wed) 07 Dec 2011 [12:34:48], Michael S. Tsirkin wrote:
    > On Wed, Dec 07, 2011 at 01:18:50AM +0530, Amit Shah wrote:
    > > Now to not race with a host issuing ballooning requests while we are in
    > > the process of freezing, we just exit from the vballoon kthread when the
    > > processes are asked to freeze. Upon thaw and restore, we re-start the
    > > thread.
    >
    > ...
    >
    > > ---
    > > drivers/virtio/virtio_balloon.c | 79 ++++++++++++++++++++++++++++++++++++++-
    > > 1 files changed, 78 insertions(+), 1 deletions(-)
    > >
    > > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
    > > index 8bf99be..10ec638 100644
    > > --- a/drivers/virtio/virtio_balloon.c
    > > +++ b/drivers/virtio/virtio_balloon.c
    > > @@ -258,7 +258,13 @@ static int balloon(void *_vballoon)
    > > while (!kthread_should_stop()) {
    > > s64 diff;
    > >
    > > - try_to_freeze();
    > > + /*
    > > + * On suspend, we want to exit this thread. We will
    > > + * start a new thread on resume.
    > > + */
    > > + if (freezing(current))
    > > + break;
    > > +
    > > wait_event_interruptible(vb->config_change,
    > > (diff = towards_target(vb)) != 0
    > > || vb->need_stats_update
    >
    > ...
    >
    > Note: this relies on kthreads being frozen before devices.
    > Looking at kernel/power/hibernate.c this is the case,
    > but I think we should add a comment to note this.

    Yes, it does. And for that reason, I mentioned that stopping the
    thread doesn't buy us anything; I'll revert this change in the next
    submission.

    > Also Cc linux-pm crowd in case I got it wrong.

    Amit


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