Re: [RFC PATCH 0/9] livepatch: consistency model

From: Jiri Kosina
Date: Fri Feb 13 2015 - 09:22:21 EST

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.


Jiri Kosina
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