On Friday, 6 July 2007 11:31, Oliver Neukum wrote: > Am Freitag, 6. Juli 2007 schrieb Benjamin Herrenschmidt: > > On Fri, 2007-07-06 at 09:13 +0200, Rafael J. Wysocki wrote: > > > > > > The only reason (I know of) why we don't handle uninterruptible tasks in the > > > freezer is that we're afraid of the suspend process deadlocking with an > > > uninterruptible task holding a lock, but AFAICS the probability of such an > > > event is extremely small. > > > > What would deadlock specifically ? One of the drivers trying to acquire > > that lock ? It would be a driver bug then. > > Your driver's write method looks like: > > mutex_lock(); > poke_some_hardware(); > wait_event_uninterruptible(); //for result > res = evaluate_result(); > mutex_unlock(); > return res; > > If you put a task into the refrigerator at wait_event_interruptible() > you will deadlock if you need this lock for the driver to go to suspend. > The suspend method then must not take the lock _and_ it must be > aware that there may be an ongoing operation. s/interruptible/uninterruptible/ > you will deadlock if you need this lock for the driver to go to suspend. > The suspend method then must not take the lock _and_ it must be > aware that there may be an ongoing operation. Well, is there any driver in the tree that works like that _and_ has a .suspend() method requiring the same lock? Besides, I'm not going to put the task into the refrigerator at that point. Please read http://lkml.org/lkml/2007/7/6/71 Moreover, I claim that, in the context of your example, _if_ the task is stuck at the wait_event_uninterruptible(), _then_ the freezerless suspend will deadlock with the task. 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
