Re: Async suspend-resume patch w/ completions (was: Re: Async suspend-resume patch w/ rwsems)

Alan Stern
2009-12-10T22:16:56Z

On Thu, 10 Dec 2009, Rafael J. Wysocki wrote:

> > You should see how badly lockdep complains about the rwsems. If it
> > really doesn't like them then using completions makes sense.
>
> It does complain about them, but when the nested _down operations are marked
> as nested, it stops complaining (that's in the version where there's no async
> in the _noirq phases).

Did you set the async_suspend flag for any devices during the test?
And did you run more than one suspend/resume cycle?

> +extern int __dpm_wait(struct device *dev, void *ign);
> +
> +static inline void dpm_wait(struct device *dev)
> +{
> + __dpm_wait(dev, NULL);
> +}

Sorry, I intended to mention this before but forgot. This design is
inelegant. You shouldn't have inlines calling functions with extra
unused arguments; they just waste code space. Make dpm_wait() be a
real routine and add a shim to the device_for_each_child() loop.

> @@ -366,7 +388,7 @@ void dpm_resume_noirq(pm_message_t state
>
> mutex_lock(&dpm_list_mtx);
> transition_started = false;
> - list_for_each_entry(dev, &dpm_list, power.entry)
> + list_for_each_entry(dev, &dpm_list, power.entry) {
> if (dev->power.status > DPM_OFF) {
> int error;
>
> @@ -375,23 +397,27 @@ void dpm_resume_noirq(pm_message_t state
> if (error)
> pm_dev_err(dev, state, " early", error);
> }
> + /* Needed by the subsequent dpm_resume(). */
> + INIT_COMPLETION(dev->power.completion);

You're still doing it. Don't initialize the completions in a totally
different phase! Initialize them directly before they are used.
Namely, at the start of device_resume() and device_suspend().

One more thing. A logical time to check for errors is just after
waiting for the children in __device_suspend(), instead of beforehand
in async_suspend(). After all, if an error occurs then it's likely to
happen while we are waiting.

Alan Stern