On Tue, 6 May 2014, Steven Rostedt wrote:
> > However, I also think if users can accept such freezing wait-time,
> > it means they can also accept kexec based "checkpoint-restart" patching.
> > So, I think the final goal of the kpatch will be live patching without
> > stopping the machine. I'm discussing the issue on github #138, but that is
> > off-topic. :)
>
> I agree with Ingo too. Being conservative at first is the right
> approach here. We should start out with a stop_machine making sure that
> everything is sane before we continue. Sure, that's not much different
> than a kexec, but lets take things one step at a time.
>
> ftrace did the stop_machine (and still does for some archs), and slowly
> moved to a more efficient method. kpatch/kgraft should follow suit.
I don't really agree here.
I actually believe that "lazy" switching kgraft is doing provides a little
bit more in the sense of consistency than stop_machine()-based aproach.
Consider this scenario:
void foo()
{
for (i=0; i<10000; i++) {
bar(i);
something_else(i);
}
}
Let's say you want to live-patch bar(). With stop_machine()-based aproach,
you can easily end-up with old bar() and new bar() being called in two
consecutive iterations before the loop is even exited, right? (especially
on preemptible kernel, or if something_else() goes to sleep).
With lazy-switching implemented in kgraft, this can never happen.
So I'd like to ask for a little bit more explanation why you think the
stop_machine()-based patching provides more sanity/consistency assurance
than the lazy switching we're doing.
Thanks a lot,
--
Jiri Kosina
SUSE Labs
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
