On Sun, 28 May 2006 00:20:30 -0400 Kumba <kumba@xxxxxxxxxx> wrote: > > suggest you should open-code an smp_call_function() and put a big comment > > over it explaining why it's done this way, and why it isn't deadlocky. > > > > <tries to remember what the deadlock is> > > > > If CPU A is running smp_call_function() it's waiting for CPU B to run the > > handler. > > > > But if CPU B is presently _also_ running smp_call_function(), it's waiting > > for CPU A to run the handler. > > > > If either of those CPUs is waiting for the other with local interrupts > > disabled, that CPU will never respond to the other CPU's IPI and they'll > > deadlock. > > The catch is, the system being affected here is strictly a UP machine. It's > impossible to make an O2 go SMP. Yup. But again, the reasons for that change to on_each_cpu() were to make all instances of the the callback function run under the same environment in all cases. That's a good change. If the platform _knows_ that it's safe to do normally-unsafe things then as I say, it shold special-case that case. Here, if the call is in O2-only code then we don't need on_each_cpu() at all - just call the function instead. If the call is in board-neutral MIPS code then things get more complicated. Sure, the code is safe on UP, but it might be deadlocky on SMP. It needs to be thought about and a suitable UP&&SMP fix needs to be found. Can someone point me at the code we're talking about here? file-n-line?
