linux-kernel - Re: [PATCH 1/2] livepatch: Implement separate coming and going module notifiers

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Date:	Fri, 29 Jan 2016 14:29:50 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Miroslav Benes <mbenes@...e.cz>
Cc:	Josh Poimboeuf <jpoimboe@...hat.com>, Jessica Yu <jeyu@...hat.com>,
	Seth Jennings <sjenning@...hat.com>,
	Jiri Kosina <jikos@...nel.org>,
	Vojtech Pavlik <vojtech@...e.com>,
	Ingo Molnar <mingo@...hat.com>, live-patching@...r.kernel.org,
	linux-kernel@...r.kernel.org, Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH 1/2] livepatch: Implement separate coming and going
 module notifiers

On Fri, 29 Jan 2016 20:25:15 +0100 (CET)
Miroslav Benes <mbenes@...e.cz> wrote:

> It is possible to achieve the same goal even with the notifiers. They are 
> processed synchronously in complete_formation(). So we can put our klp 
> hook after that, right? Or better, put it to load_module() after 
> complete_formation() call. There is an error handling code even today 
> (that is, parse_args() or mod_sysfs_setup() can fail). Moreover, we'll 
> have a hook there with Jessica's relocation rework patch set.

The problem with notifiers is that you don't know what is being called.
A function call directly in the code, where it will always be needed if
configured in, is a reasonable need to not use a notifier.

Although, I have to admit, if live kernel patching is configured in,
it's not always needed to be called here, does it? With ftrace, the
call has to be done when ftrace is configured in regardless if tracing
is used or not.

> 
> But Steven's reasoning is convincing, so I'm all up for it.

Great!

-- Steve