On Monday 29 June 2009, Alan Stern wrote: > On Mon, 29 Jun 2009, Rafael J. Wysocki wrote: > > > Well, not only in that cases and in fact this is where the actual problem is. > > > > Namely, pm_request_suspend() and pm_request_resume() have to cancel any > > pending requests in a reliable way so that the work struct can be used safely > > after they've returned. > > Right. > > > Assume for example that there's a suspend request pending while > > pm_request_resume() is being called. pm_request_resume() uses > > cancel_delayed_work() to kill off the request, but that's in interrupt and it > > happens to return -1. Now, there's pm_runtime_put_atomic() right after that > > which attempts to queue up an idle notification request before the > > delayed suspend request has a chance to run and bad things happen. > > > > So, it seems, pm_request_resume() can't kill suspend requests by itself > > and instead it has to queue up resume requests for this purpose, which > > brings us right back to the problem of two requests queued up at a time > > (a delayed suspend request and a resume request that is supposed to cancel it). > > No, you're trying to do too much. If the state is RPM_IDLE (i.e., a > suspend request is pending) then rpm_request_resume doesn't need to do > anything. The device is already resumed! Sure, it can try to kill the > request and change the state to RPM_ACTIVE, but it doesn't need to. I think it does need to do that, because the reuqest may be scheduled way in the future and we can't preserve its work structure until it runs. pm_request_resume() doesn't know in advance when the suspend work function is going to be queued up and run. > Think about it. Even if the suspend request were killed off, there's > always the possibility that someone could call rpm_runtime_suspend > right afterward. If the driver really wants to resume the device and > prevent it from suspending again, then the driver should call > pm_runtime_get before pm_request_resume. Then it won't matter if the > suspend request runs. No, it doesn't matter if the request runs, but it does matter if the work structure used for queuing it up may be used for another purpose. :-) > > Nevertheless, using your workqueue patch we can still simplify things quite a > > bit, so I think it's worth doing anyway. > > Me too. :-) > > > > Which reminds me... The way you've got things set up, > > > pm_runtime_put_atomic queues an idle notification, right? That's > > > a little inconsistent with the naming of the other routines. > > > > > > Instead, pm_runtime_put_atomic should be a version of pm_runtime_put > > > that can safely be called in an atomic context -- it implies that it > > > will call the runtime_notify callback while holding the spinlock. The > > > routine to queue an idle-notify request should be called something like > > > pm_request_put -- although that name isn't so great because it sounds > > > like the put gets deferred instead of the notification. > > > > There can be pm_request_put() and pm_request_put_sync(), for example. > > Or pm_request_put_async() and pm_request_put(), depending on which version is > > going to be used more often. > > I don't follow you. We only need one version of pm_request_put. Did > you mean "pm_runtime_put" and "pm_runtime_put_async"? That would make > sense. Yes, I did, sorry. > If you use that (instead of pm_request_put) then would you want to > similarly rename pm_request_resume and pm_request_suspend to > pm_runtime_resume_async and pm_runtime_suspend_async? Well, I think the pm_request_[suspend|resume] names are better. :-) The problem with pm_<something>_put is that it does two things at a time, decrements the resume counter and runs or queues up an idle notification. Perhaps it's a good idea to call it after the second thing and change pm_runtime_get() to pm_runtime_inuse(), so that we have: * pm_runtime_inuse() - increment the resume counter * pm_runtime_idle() - decrement the resume counter and run idle notification * pm_request_idle() - decrement the resume counter and queue idle notification and __pm_runtime_idle() as the "bare" idle notification function? Thanks, Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
