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. Miroslav -- 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
