On Thu, Jul 20, 2017 at 05:50:04PM +0200, Petr Mladek wrote: > On Wed 2017-07-19 23:17:23, Josh Poimboeuf wrote: > > - patching otherwise unpatchable code (i.e., assembly) > > > > In many/most cases, it seems like stop_machine() would be very useful > > to avoid concurrency issues. > > I am not sure if stop_machine() would help here. It would make sense > in kPatch where also the ftrace handlers are added during > stop_machine(). Then it is possible to synchronize both operations > (hooks, enabling ftrace handlers) and do everything "atomically". > > IMHO, the big advantage of livepatch framework is that stop_machine() > is not needed. I hope that it will stay this way. > > Also it might need some additional support. You would want to stop > the machine to make sure that it is safe to do a change. Then > we might need to check stacks, ... Don't worry. I much prefer our current consistency model to kpatch, and I have no intention of changing it :-) That said, for the hooks, I still think stop_machine() will be helpful in some cases where you need to ensure no other code is running. Like the stack_segment patch I posted, for example. Anyway I'm not suggesting we do the stop_machine() in livepatch code itself. I'm just hoping it will work from a hook, in case the patch author needs to do it as a last resort. -- Josh -- To unsubscribe from this list: send the line "unsubscribe live-patching" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
