Re: live patching design (was: Re: [PATCH 1/3] sched: add sched_task_call())

From: Josh Poimboeuf
Date: Fri Feb 20 2015 - 17:09:29 EST

On Fri, Feb 20, 2015 at 10:46:13PM +0100, Vojtech Pavlik wrote:
> On Fri, Feb 20, 2015 at 08:49:01PM +0100, Ingo Molnar wrote:
> > I.e. it's in essence the strong stop-all atomic patching
> > model of 'kpatch', combined with the reliable avoidance of
> > kernel stacks that 'kgraft' uses.
> > That should be the starting point, because it's the most
> > reliable method.
> In the consistency models discussion, this was marked the
> "LEAVE_KERNEL+SWITCH_KERNEL" model. It's indeed the strongest model of
> all, but also comes at the highest cost in terms of impact on running
> tasks. It's so high (the interruption may be seconds or more) that it
> was deemed not worth implementing.

Yeah, this is way too disruptive to the user.

Even the comparatively tiny latency caused by kpatch's use of
stop_machine() was considered unacceptable by some.

Plus a lot of processes would see EINTR, causing more havoc.

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