On Monday, November 29, 2010, Alan Stern wrote: > On Sun, 28 Nov 2010, Rafael J. Wysocki wrote: > > > On Sunday, November 28, 2010, Alan Stern wrote: > > > On Sun, 28 Nov 2010, Rafael J. Wysocki wrote: > > > > > > > From: Rafael J. Wysocki <rjw@xxxxxxx> > > > > > > > > Currently dpm_prepare() returns error code if it finds that a device > > > > being suspended has a pending runtime resume request. However, it > > > > should not do that if the checking for wakeup events is not enabled. > > > > > > It doesn't. The line you changed _does_ check device_may_wakeup(). > > > > That's not the point. The problem is that it shouldn't abort suspend > > when events_check_enabled is unset. > > Oh, I see. This is a tricky issue. Every driver for a device that can > have wakeup-enabled children needs to worry about the race between > suspending the device and receiving a wakeup request from a child. > For example, in drivers/usb/core/hcd-pci.c, the suspend_common() > routine goes out of its way to return -EBUSY if device_may_wakeup() is > true and the controller's root hub has a pending wakeup request. > > How should drivers handle this in general? Should we make an effort to > convert them to use the wakeup framework so they they can let the PM > core take care of these races? I think so. We also need to put a pm_check_wakeup_events() check into dpm_suspend() IMO, so that we abort the suspending of devices as soon as a wakeup event is reported. > Do we have to consider similar races during runtime suspend? Ideally, yes, but I'm not sure if that's generally possible. IMO, it won't be a big deal if a parent device is suspended and immediately resumed occasionally due to a pending wakeup signal from one of its children. It may be a problem if that happens too often, though. > > > > On the other hand, if the checking for wakeup events is enabled, it > > > > can return error when a wakeup event is detected, regardless of its > > > > source. > > > > > > Will adding this call to pm_wakeup_event() end up double-counting some > > > events? > > > > Yes, it will, if the event has already been reported by the subsystem or driver. > > > > I don't think it's a very big issue and I'm not sure trying to avoid it is > > worth the effort (we can check if the device's wakeup source object is active > > and skip reporting the wakeup event in that case, but that doesn't guarantee > > that the event won't be counted twice anyway). > > I agree that it's not a big issue. Wakeups reported twice because they > occur just before a system sleep won't cause serious accounting > problems and probably won't happen very often anyway. I just wanted to > make sure that the issue wasn't being ignored by mistake. OK Does it mean you're fine with the patch? Rafael _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
