On Sat, 4 Aug 2012, Rafael J. Wysocki wrote: > > What happens if a system sleep begins after > > pm_runtime_async_resume_and_call() but before the runtime resume? When > > the system wakes up, the device will be back at full power without ever > > executing a runtime PM call. Then how will func get invoked? > > The pm_runtime_barrier() at the beginning of __device_suspend() guarantees > that if there's a resume request pending at this point, the resume will be > carried out. I think we can modify rpm_resume() to return only after func() > is executed, so there shouldn't be a problem with that particular case. A resume request can get added to the workqueue after __device_suspend() runs, in which case the problem will still exist. Should pm_runtime_set_active() call func (if such a call is pending)? > > What happens if the driver is unbound after > > pm_runtime_async_resume_and_call() but before the runtime resume? The > > When the runtime resume occurs, func will be invoked -- and the driver > > might not even be in memory any more. > > We have no protection against that at the moment, but then there is no > guarantee that the driver's runtime PM callbacks won't be run after > it's been unbound. True. We have been relying on the subsystem to handle this race, but obviously that's no good if the callback is directly to the driver. I don't see any way to fix this in the PM core. > Perhaps we should run pm_runtime_barrier() before executing .remove() > in __device_release_driver() We already do pm_runtime_get_sync() and pm_runtime_put_sync(). I'm not sure how necessary those calls really are ... but pm_runtime_barrier() would be redundant. > (and perhaps run pm_runtime_idle() afterwards > in case the subsystem or PM domain knows how to power down the device even if > there's no driver) and expect .remove() to clean up? I can't think of anything wrong with calling pm_runtime_idle() at the end of __device_release_driver(). Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
