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

From: Jiri Kosina <jkosina@suse.cz>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
	Ingo Molnar <mingo@redhat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
	live-patching@vger.kernel.org, linux-kernel@vger.kernel.org,
	Seth Jennings <sjenning@redhat.com>,
	Vojtech Pavlik <vojtech@suse.cz>
Subject: Re: [RFC PATCH 6/9] livepatch: create per-task consistency model
Date: Thu, 12 Feb 2015 13:25:14 +0100 (CET)	[thread overview]
Message-ID: <alpine.LNX.2.00.1502121319440.20672@pobox.suse.cz> (raw)
In-Reply-To: <20150212115628.GL2896@worktop.programming.kicks-ass.net>

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
SUSE Labs