Re: use of pm_runtime_disable() from driver probe?

Rafael J. Wysocki
2012-07-11T17:36:45Z

On Wednesday, July 11, 2012, Alan Stern wrote:
> On Wed, 11 Jul 2012, Rafael J. Wysocki wrote:
>
> > > This opens up the possibility of calling probe while a runtime resume
> > > or suspend is in progress. (On the other hand, the existing code
> > > doesn't prevent a concurrent runtime resume.) Maybe it would be best
> > > to leave the pm_runtime_barrier().
> >
> > That wouldn't close the race, though, because the suspend/resume may still
> > be started right after _barrier has returned.
>
> True, but see below.
>
> > The race is only possible if runtime PM is enabled by a subsystem or PM domain
> > code before the first eligible driver is registered and if that code is not
> > careful enough to get ready for driver registration. I'm not sure how likely
> > it is to happen in practice.
>
> It's not just the first eligible driver. Drivers can be bound and
> unbound dynamically, and suspends/resume operations can sit on the wait
> queue or wait until a timer expires. We don't want an old request
> suddenly to take effect in the middle of a probe.
>
> The barrier will get rid of any old requests. New ones would have to
> be added after the probe starts, which as you say, is unlikely.

OK, I'll keep the barrier, then.

Kevin, can you please double check the patch below?

Rafael

---
drivers/base/dd.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)

Index: linux/drivers/base/dd.c
===================================================================
--- linux.orig/drivers/base/dd.c
+++ linux/drivers/base/dd.c
@@ -356,10 +356,9 @@ int driver_probe_device(struct device_dr
pr_debug("bus: '%s': %s: matched device %s with driver %s\n",
drv->bus->name, __func__, dev_name(dev), drv->name);

- pm_runtime_get_noresume(dev);
pm_runtime_barrier(dev);
ret = really_probe(dev, drv);
- pm_runtime_put_sync(dev);
+ pm_runtime_idle(dev);

return ret;
}
@@ -406,9 +405,8 @@ int device_attach(struct device *dev)
ret = 0;
}
} else {
- pm_runtime_get_noresume(dev);
ret = bus_for_each_drv(dev->bus, NULL, dev, __device_attach);
- pm_runtime_put_sync(dev);
+ pm_runtime_idle(dev);
}
out_unlock:
device_unlock(dev);