On Tuesday, September 15, 2015 03:18:19 PM Alan Stern wrote: > On Tue, 15 Sep 2015, Thierry Reding wrote: > > > > There are a few things to watch out for. Since the dpm_list gets > > > modified during system sleep transitions, we would have to make sure > > > that nothing gets probed during those times. In principle, that's what > > > the "prepare" stage is meant for, but there's still a race. As long as > > > no other kernel thread (such as the deferred probing mechanism) tries > > > to probe a device once everything has been frozen, we should be okay. > > > But if not, there will be trouble -- after the ->prepare callback runs, > > > the device is no longer on the dpm_list and so we don't want this patch > > > to put it back on that list. > > > > Perhaps moving to the end of the list needs to be a little smarter. That > > is it could check whether the device has been prepared for suspension or > > not and only move when it hasn't? > > Maybe. But doesn't that mean it won't solve your problem completely? > > > Then again, shouldn't the core even prohibit new probes once the suspend > > has been triggered? Sounds like asking for a lot of trouble if it didn't > > ... > > The core prohibits new devices from being registered. It does not > prohibit probes of existing devices, because they currently do not > affect the dpm_list.
Which may be a mistake, because it does affect callbacks executed during suspend/resume (after successful probe the device potentially has a different set of PM callbacks than before). > In general, we rely on subsystems not to do any probing once a device > is suspended. It's probably reasonable to ask them not to do any > probing once a device has gone through the "prepare" stage. Right. Question is when it should be allowed to probe again. I guess at the same time we allow registrations to to take place again? Thanks, Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
