linux-kernel - Re: [PATCH v3] kprobes: Disable Kprobe when ftrace arming fails

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Date:	Tue, 24 Mar 2015 00:32:46 +0100 (CET)
From:	Jiri Kosina <jkosina@...e.cz>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
cc:	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...nel.org>, Petr Mladek <pmladek@...e.cz>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	"David S. Miller" <davem@...emloft.net>,
	Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
	Ananth NMavinakayanahalli <ananth@...ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] kprobes: Disable Kprobe when ftrace arming fails

On Mon, 23 Mar 2015, Paul E. McKenney wrote:

> > > Even if it was documented (it isn't), it's pretty weird terminology - 
> > > please use clearer formulations, like 'patched function' or 'unpatched 
> > > function' or 'function with pending patch'. No need to redefine 
> > > existing words in a weird fashion just to create the appearance of 
> > > being special ...
> > > 
> > 
> > I think it has to do with their RCU like patching functionality, where
> > some tasks are still executing the old function and others are
> > executing the new function. In RCU, there's two "universes" too. One
> > with the old value, and one with the new. After the grace period has
> > finished, everything is back to a single "universe".
> > 
> > I'm not sure RCU uses the term "universe" though. Paul?
> 
> I have used "version" for what you call "universe", but mostly in
> "intro to RCU" guest lectures.

Yup, exactly. Even kGraft (which is where the 'universe' term referring to 
the function versioning in lazy migration is very likely coming from) 
doesn't really use the term 'universe' itself anywhere in the sources as 
any kind of identifier. It's always used solely as a term that's intended 
to simplify the basic understanding of how the whole process works, and 
that's pretty much it. I don't even think it deserves so lively discussion 
:)

Thanks,

-- 
Jiri Kosina
SUSE Labs
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