On Sat, 18 Jun 2011, Rafael J. Wysocki wrote:
> On Friday, June 17, 2011, Rafael J. Wysocki wrote:
> > On Friday, June 17, 2011, Alan Stern wrote:
> > > On Fri, 17 Jun 2011, Rafael J. Wysocki wrote:
> > >
> > > > Having considered that a bit more I see that, in fact, commit
> > > > e8665002477f0278f84f898145b1f141ba26ee26 (PM: Allow
> > > > pm_runtime_suspend() to
> > > > succeed during system suspend) has introduced at least one regression.
> > > > Namely, the PCI bus type runs pm_runtime_resume() in its .prepare()
> > > > callback to guarantee that devices will be in a well known state before
> > > > the PCI .suspend() and .suspend_noirq() callbacks are executed.
> > > > Unfortunately, after commit e8665002477f0278f84f898145b1f141ba26ee26
> > > > this
> > > > isn't valid any more, because devices can be runtime-suspend after the
> > > > pm_runtime_resume() in .prepare() has run.
> > > >
> > > > USB seems to do something similar in choose_wakeup().
> > > >
> > > > So, either the both of these subsystems should be modified to use
> > > > pm_runtime_get_sync() and then pm_runtime_put_<something>() some time
> > > > during resume, or we should revert commit
> > > > e8665002477f0278f84f898145b1f141ba26ee26.
> > >
> > > pm_runtime_put_noidle would be appropriate.
> > >
> > > > Quite frankly, which shouldn't be a surprise to anyone at this point,
> > > > I'd
> > > > prefer to revert that commit for 3.0.
> > >
> > > Maybe we can compromise. Instead of reverting that commit outright,
> > > put the get_noresume just before the suspend callback and put the
> > > put_sync just after the resume callback.
> >
> > That wouldn't fix the PCI problem, though, because it would leave a small
> > window in which the device could be suspended after the pm_runtime_resume()
> > in pci_pm_prepare() had run.
>
> That said, the PCI case can be solved with a separate patch and if the other
> subsystems are not affected, perhaps that's the best approach.
Yes, it would be a simple change.
> Still, I'd like to make sure that there won't be any races between runtime
> PM and .suspend_noirq() and .resume_noirq() callbacks, so I'd like to apply
> the patch below.
>
> Thanks,
> Rafael
>
> ---
> drivers/base/power/main.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> 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
> @@ -591,6 +591,8 @@ void dpm_resume(pm_message_t state)
> async_error = 0;
>
> list_for_each_entry(dev, &dpm_suspended_list, power.entry) {
> + pm_runtime_get_noresume(dev);
> + pm_runtime_enable(dev);
> INIT_COMPLETION(dev->power.completion);
> if (is_async(dev)) {
> get_device(dev);
> @@ -614,6 +616,7 @@ void dpm_resume(pm_message_t state)
> }
> if (!list_empty(&dev->power.entry))
> list_move_tail(&dev->power.entry, &dpm_prepared_list);
> + pm_runtime_put_noidle(dev);
> put_device(dev);
> }
> mutex_unlock(&dpm_list_mtx);
> @@ -939,8 +942,10 @@ int dpm_suspend(pm_message_t state)
> put_device(dev);
> break;
> }
> - if (!list_empty(&dev->power.entry))
> + if (!list_empty(&dev->power.entry)) {
> list_move(&dev->power.entry, &dpm_suspended_list);
> + pm_runtime_disable(dev);
> + }
The put_noidle is in the wrong place for async resumes. Likewise for
the pm_runtime_disable() and async suspends. Also this runs into
problems if a device is never suspended (i.e., if the sleep transition
aborts before suspending that device).
I have been working on a similar patch to do these things. But it got
derailed by the problems mentioned earlier in the other email thread
(and the bug fix I posted yesterday). Maybe I can send it in early
next week.
Alan Stern
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