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    SubjectRe: [RFC][PATCH] PM: Introduce new top level suspend and hibernation callbacks (rev. 3)
    On Mon, 24 Mar 2008, Rafael J. Wysocki wrote:

    > Hi,
    >
    > This is the 3rd revision of the patch introducing new callbacks for suspend
    > and hibernation. It has been tested on x86-64.
    ...
    > * The registrations of parentless devices are disabled before the first
    > ->prepare() method is called and enabled before the first ->resume() method
    > is called

    It would be okay to wait until after the last prepare() method is
    called. I don't know if it makes any difference in the end, however.

    > +enum dpm_state {
    > + DPM_ON,
    > + DPM_RESUMING,
    > + DPM_SUSPENDING,
    > + DPM_OFF,
    > + DPM_OFF_IRQ,
    > +};

    Can we also have a DPM_PREPARING state, set when ->prepare() is about
    to be called? The PM core wouldn't make use of it but some drivers
    would. (I can't think of any use at all for the analogous
    DPM_COMPLETING state, however.)

    > @@ -68,22 +59,30 @@ int device_pm_add(struct device *dev)
    ...
    > + if (dev->parent) {
    > + if (dev->parent->power.status > DPM_RESUMING) {

    Clearer to say: if (dev->parent->power.status >= DPM_SUSPENDING) {

    ...
    > + } else if (transition_started) {
    > + /*
    > + * We refuse to register parentless devices while a PM
    > + * transition is in progress in order to avoid leaving them
    > + * unhandled down the road
    > + */

    Log a warning here? If this ever happened, it would be the sort of
    unexpected regression that people get all excited about.

    > + goto Refuse;
    > }
    ...

    > +static void dpm_resume(pm_message_t state)
    > +{
    > + struct list_head list;
    > +
    > + INIT_LIST_HEAD(&list);
    > + mutex_lock(&dpm_list_mtx);
    > + transition_started = false;
    > + while (!list_empty(&dpm_list)) {
    > + struct device *dev = to_device(dpm_list.next);
    > +
    > + if (dev->power.status > DPM_SUSPENDING) {

    Clearer to say: if (dev->power.status >= DPM_OFF) {

    Note that if dev->power.status is equal to DPM_SUSPENDING then you
    don't want to call resume_device(), but you still do want to change
    dev->power.status to DPM_RESUMING so that new children can be
    registered.

    > + dev->power.status = DPM_RESUMING;
    > + get_device(dev);
    > + mutex_unlock(&dpm_list_mtx);
    > +
    > + resume_device(dev, state);
    > +
    > + mutex_lock(&dpm_list_mtx);
    > + put_device(dev);
    > + }
    > + if (!list_empty(&dev->power.entry))
    > + list_move_tail(&dev->power.entry, &list);

    A little problem here: You refer to dev after calling put_device().

    > + }
    > + list_splice(&list, &dpm_list);

    This isn't the way I imagined doing it (your extra "list"), but it's
    fine.

    ...
    > +static void dpm_complete(pm_message_t state)
    > {
    ...
    > + complete_device(dev, state);
    > +
    > + mutex_lock(&dpm_list_mtx);
    > + put_device(dev);
    > + }
    > + if (!list_empty(&dev->power.entry))
    > + list_move(&dev->power.entry, &list);

    Same problem with use-after-put. Also present in dpm_prepare().

    > }
    > + list_splice(&list, &dpm_list);
    > mutex_unlock(&dpm_list_mtx);
    > }

    ...
    > static int dpm_suspend(pm_message_t state)
    > {
    ...
    > error = suspend_device(dev, state);
    > +
    > mutex_lock(&dpm_list_mtx);
    > + put_device(dev);
    > if (error) {
    > printk(KERN_ERR "Could not suspend device %s: "
    > - "error %d%s\n",
    > - kobject_name(&dev->kobj),
    > - error,
    > - (error == -EAGAIN ?
    > - " (please convert to suspend_late)" :
    > - ""));
    > - dev->power.sleeping = false;
    > + "error %d\n", kobject_name(&dev->kobj), error);
    > + list_splice_init(&dpm_list, &list);
    > break;
    > }
    > - if (!list_empty(&dev->power.entry))
    > - list_move(&dev->power.entry, &dpm_off);
    > + if (!list_empty(&dev->power.entry)) {
    > + dev->power.status = DPM_OFF;
    > + list_move(&dev->power.entry, &list);
    > + }

    Use-after-put again.

    > }
    > - if (!error)
    > - all_sleeping = true;
    > + list_splice(&list, &dpm_list);

    Instead you could eliminate the list_splice_init() above and put here:

    list_splice(&list, dpm_list->prev);

    This will move the entries from list to the end of dpm_list.

    > mutex_unlock(&dpm_list_mtx);
    > + return error;
    > +}

    On the whole it looks quite good.

    Alan Stern



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