linux-kernel - Re: live patching design (was: Re: [PATCH 1/3] sched: add sched_task

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Date:	Fri, 20 Feb 2015 16:08:45 -0600
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Vojtech Pavlik <vojtech@...e.com>
Cc:	Ingo Molnar <mingo@...nel.org>, Jiri Kosina <jkosina@...e.cz>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>,
	Seth Jennings <sjenning@...hat.com>,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: live patching design (was: Re: [PATCH 1/3] sched: add
 sched_task_call())

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.

-- 
Josh
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