On Fri, Feb 13, 2015 at 03:40:14PM +0100, Miroslav Benes wrote: > On Fri, 13 Feb 2015, Jiri Kosina wrote: > > > On Fri, 13 Feb 2015, Josh Poimboeuf wrote: > > > > > > How about we take a slightly different aproach -- put a probe (or ftrace) > > > > on __switch_to() during a klp transition period, and examine stacktraces > > > > for tasks that are just about to start running from there? > > > > > > > > The only tasks that would not be covered by this would be purely CPU-bound > > > > tasks that never schedule. But we are likely in trouble with those anyway, > > > > because odds are that non-rescheduling CPU-bound tasks are also > > > > RT-priority tasks running on isolated CPUs, which we will fail to handle > > > > anyway. > > > > > > > > I think Masami used similar trick in his kpatch-without-stopmachine > > > > aproach. > > > > > > Yeah, that's definitely an option, though I'm really not too crazy about > > > it. Hooking into the scheduler is kind of scary and disruptive. > > > > This is basically about running a stack checking for ->next before > > switching to it, i.e. read-only operation (admittedly inducing some > > latency, but that's the same with locking the runqueue). And only when in > > transition phase. > > > > > We'd also have to wake up all the sleeping processes. > > > > Yes, I don't think there is a way around that. > > I think there are two options how to do it if I understand you correctly. > > 1. we would put a probe on __switch_to and afterwards wake up all the > sleeping processes. > > 2. we would do it in an asynchronous manner. We would put a probe and let > the processes to wake themselves. The transition delayed workqueue > would only check if there is some non-migrated process. Of course if > some process sleeps for a long time it would take a long time to > complete the patching. It would be up to the user to send a signal to > the process to wake up. > > Does it make sense? If yes, I cannot decide which approach is better. Option 2 wouldn't really work for kthreads because you can't signal them to wake up from user space. And I really want to avoid having to leave the system in a partially patched state for a long period of time. But also option 1 wouldn't necessarily result in the system being immediately patched, since you could have some CPU-bound tasks. So some asynchronous patching is still needed. -- 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
