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.) 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. Binding and unbinding aren't an issue once the PM core owns all the device semaphores. Alan Stern _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
