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

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Message-ID: <alpine.LNX.2.00.1503232330320.6781@pobox.suse.cz>
Date:	Mon, 23 Mar 2015 23:36:00 +0100 (CET)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Ingo Molnar <mingo@...nel.org>
cc:	Steven Rostedt <rostedt@...dmis.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, Ingo Molnar wrote:

> > > > wth is a 'universe' in this context?
> > > 
> > > We use the term "universe" to define whether the system or task uses
> > > original or patched functions. It is especially important for patches
> > > that modify semantic of functions. They need more complex consistency
> > > model. It defines when it is safe time for the system or task to start
> > > using the new functions (switch to the new universe).
> > > 
> > > In theory, different tasks might be in more universes if more patches are
> > > being applied. In practice, we deal with only two universes. The trick is
> > > that we allow to add new patch only when the whole system has switched
> > > to the previous one.
> > > 
> > 
> > Is this terminology documented anywhere upstream yet?
> 
> Even if it was documented (it isn't), 

There is no point in documenting it upstream, as no upstream code is using 
this "universe" notation. It should just be removed from original Petr's 
changelog and that's it.

> it's pretty weird terminology - please use clearer formulations, like 
> 'patched function' or 'unpatched function' or 'function with pending 
> patch'.

All your suggestions above unfortunately don't really reflect what is 
happening when lazy per-thread migration is applied.

> No need to redefine existing words in a weird fashion just to create the 
> appearance of being special ...

So which particular existing word(s) are you talking about here?

Thanks,

-- 
Jiri Kosina
SUSE Labs
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