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Date: Tue, 24 Mar 2015 08:59:25 +0100
From: Petr Mladek <pmladek@suse.cz>
To: Jiri Kosina <jkosina@suse.cz>
Cc: Ingo Molnar <mingo@kernel.org>, Steven Rostedt <rostedt@goodmis.org>,
        Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
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        Ananth NMavinakayanahalli <ananth@in.ibm.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3] kprobes: Disable Kprobe when ftrace arming fails
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On Mon 2015-03-23 23:36:00, Jiri Kosina wrote:
> 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.

Note that the term "universe" is not used in the commit message => no
change is needed.

I used the term to answer the question about interference between
Jprobes, ftrace, and live patches. I am sorry again. I should have
described it in a broader context.


Anyway, please, let me to repeat. This patch makes sense even without
live patching. The ftrace operations were there even before and might
have failed.

Best Regards,
Petr