On Tuesday, 31 July 2007 17:24, Alan Stern wrote: > On Tue, 31 Jul 2007, Rafael J. Wysocki wrote: > > > > > One thought was to have the PM core acquire and hold the dpm_list_mutex > > > > throughout the suspend. This would block registration attempts at the > > > > point where the new device is added to the PM core's device-list. > > > > > > > > > > I think blocking at this point is too late - many drivers muck with > > > the device in different ways before registering the "result" with > > > driver core. The device may be half-awaken by then. > > > An alternative could be to have a rwsem taken for writing by the PM core and > > for reading by registration/binding/unbinding (and other suspend-sensitive code > > paths). > > I think this is subject to the same weakness Dmitry mentions: By the > time the driver would block on the new rwsem, it has already started > mucking with the device. Worse yet, it may hold a mutex that the > suspend method needs, thereby deadlocking the suspend. (That's what > would happen with serio->drv_mutex in the input layer.) Not if the rule is that the "suspend" rwsem should be acquired before any other locks and before the device is actually accessed. > Maybe the best answer is simply to fail all attempts at device > registration while a suspend is underway. At least that is a known > error path which drivers are prepared (in theory) to deal with. It > could be implemented quite easily with an rwsem, by making the > registration code use down_read_trylock. Yes. > Binding and unbinding aren't an issue once the PM core owns all the > device semaphores. Yes, but currently they aren't held accross the entire suspend. Greetings, Rafael -- "Premature optimization is the root of all evil." - Donald Knuth _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
