Re: [RFC PATCH 6/9] livepatch: create per-task consistency model

From: Jiri Kosina
Date: Thu Feb 12 2015 - 07:25:24 EST

On Thu, 12 Feb 2015, Peter Zijlstra wrote:

> Its not at all clear how all this would work to me. And I'm not
> motivated enough to go try and reverse engineer your patch; IMO
> livepatching is utter fail.
> If your infrastructure relies on the uptime of a single machine you've
> lost already.

Well, the fact indisputable fact is that there is a demand for this. It's
not about one machine, it's about scheduling dowtimes of datacentres.

But if this needs to be discussed, it should be done outside of this
thread I guess.

> FWIW, the barriers in klp_update_task_universe() and
> klp_set_universe_goal() look like complete crack, and their comments are
> seriously deficient.

These particular barriers seem correct to me; you basically need to make
sure that whenever a thread with TIF_KLP_NEED_UPDATE goes through
do_notify_resume(), it sees proper universe number to be converted to.

Jiri Kosina
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