On Fri, 7 Aug 2009, Peter Zijlstra wrote: > On Fri, 2009-08-07 at 12:45 -0400, Alan Stern wrote: > > On Fri, 7 Aug 2009, Peter Zijlstra wrote: > > > > The other proposal was creating a fixed list of classes and register > > > each device at a class corresponding to its depth in the tree. I can't > > > remember what was wrong with that, but I seem to have been persuaded > > > that that was hard too. > > > > It probably would work for the most part. However a possible scenario > > involves first locking a parent and then locking all its children. (I > > don't know if this ever happens anywhere, but it might.) This can't > > cause a deadlock but it would run into trouble with depth-based > > classes. > > If you know which parent is locked, we can solve that with > mutex_lock_nest_lock() [ doesn't currently exist, but is analogous to > spin_lock_nest_lock() ] and together with > http://lkml.org/lkml/2009/7/23/222 that would allow you to lock up to > 2048 children. Not only do I know not which parent is locked, I don't even know if this ever happens anywhere at all! My point was purely theoretical. > Would something like that work? Perhaps -- I don't understand what spin_lock_nest_lock() is supposed to do. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
