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SubjectRe: Async suspend-resume patch w/ rwsems (was: Re: [GIT PULL] PM updates for 2.6.33)
On Tue, 8 Dec 2009, Rafael J. Wysocki wrote:

> For completness, below is the full async suspend/resume patch with rwlocks,
> that has been (very slightly) tested and doesn't seem to break things.
>
> [Note to Alan: lockdep doesn't seem to complain about the not annotated nested
> locks.]

I can't imagine why not. And wouldn't lockdep get confused by the fact
that in the async case, the rwsems are released by a different process
from the one that acquired them?


> Index: linux-2.6/drivers/base/power/main.c
> ===================================================================
> --- linux-2.6.orig/drivers/base/power/main.c
> +++ linux-2.6/drivers/base/power/main.c

Should we have an attribute under /sys/power to disable async
suspend/resume? It would make testing easier and give people a way to
work around problems.

> @@ -334,25 +337,53 @@ static void pm_dev_err(struct device *de
> * The driver of @dev will not receive interrupts while this function is being
> * executed.
> */
> -static int device_resume_noirq(struct device *dev, pm_message_t state)
> +static int __device_resume_noirq(struct device *dev, pm_message_t state)
> {

Do you want to use async tasks in the late-suspend/early-resume stages?
I know that USB won't use it, not even for the PCI host controllers --
not unless the PCI core specifically wants it. Doing just the regular
suspend/resume stages may be enough.

> +static int device_resume_noirq(struct device *dev)
> +{
> + down_write(&dev->power.rwsem);
> +
> + if (dev->power.async_suspend && !pm_trace_is_enabled()) {

If the sysfs attribute exists, then maybe we _should_ allow async with
PM tracing enabled. I don't know; it's your decision.

atomic_set(&async_error, error);
}


> @@ -683,10 +835,12 @@ static int dpm_suspend(pm_message_t stat
>
> INIT_LIST_HEAD(&list);
> mutex_lock(&dpm_list_mtx);
> + pm_transition = state;
> while (!list_empty(&dpm_list)) {
> struct device *dev = to_device(dpm_list.prev);
>
> get_device(dev);
> + dev->power.status = DPM_OFF;

What's that for? dev->power.status is supposed to be DPM_SUSPENDING
until the suspend method is successfully completed.

> mutex_unlock(&dpm_list_mtx);
>
> error = device_suspend(dev, state);
> @@ -694,16 +848,22 @@ static int dpm_suspend(pm_message_t stat
> mutex_lock(&dpm_list_mtx);
> if (error) {
> pm_dev_err(dev, state, "", error);
> + dev->power.status = DPM_SUSPENDING;

And then this isn't needed.

> put_device(dev);
> break;
> }
> - dev->power.status = DPM_OFF;

This line has to be moved into __device_suspend(), even though it won't
be protected by dpm_list_mtx. The same sort of thing applies to
dpm_suspend_noirq() (although nothing needs to be moved if you don't
make it async).

The rest looks okay.

How about exporting a wait_for_device_to_resume() routine? Drivers
could call it for non-tree resume constraints:

void wait_for_device_to_resume(struct device *other)
{
down_read(&other->power.rwsem);
up_read(&other->power.rwsem);
}

Unfortunately there is no equivalent for non-tree suspend constraints.

Alan Stern



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