linux-kernel - Re: [PATCH v3 0/2] Fix ordering of ftrace/livepatch calls on module load and unload

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Message-ID: <20160208174846.GB23106@treble.redhat.com>
Date:	Mon, 8 Feb 2016 11:48:46 -0600
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Jessica Yu <jeyu@...hat.com>
Cc:	Seth Jennings <sjenning@...hat.com>,
	Jiri Kosina <jikos@...nel.org>,
	Vojtech Pavlik <vojtech@...e.com>,
	Miroslav Benes <mbenes@...e.cz>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>, live-patching@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/2] Fix ordering of ftrace/livepatch calls on module
 load and unload

On Fri, Feb 05, 2016 at 10:08:15PM -0500, Jessica Yu wrote:
> As explained here [1], livepatch modules are failing to initialize properly
> because the ftrace coming module notifier (which calls
> ftrace_module_enable()) runs *after* the livepatch module notifier (which
> enables the patch(es)). Thus livepatch attempts to apply patches to
> modules before ftrace_module_enable() is even called for the corresponding
> module(s). As a result, patch modules break. Ftrace code must run before
> livepatch on module load, and the reverse is true on module unload.
> 
> For ftrace and livepatch, order of initialization (plus exit/cleanup code) is
> important for loading and unloading modules, and using module notifiers to
> perform this work is not ideal since it is not always clear what gets called
> when. In this patchset, dependence on the module notifier call chain is removed
> in favor of hard coding the corresponding function calls in the module loader.
> This promotes better code visibility and ensures that ftrace and livepatch code
> get called in the correct order on patch module load and unload.
> 
> Tested the changes with a test livepatch module that patches 9p and nilfs2,
> and verified that the issue described in [1] is fixed.

Since Rusty agreed to your suggested changes for splitting up
complete_formation() and for setting mod->state = MODULE_STATE_GOING
before calling the going notifiers in the error path, can you do a v4
with those changes?  They should probably be split up like:

1. split up complete_formation()
2. set MODULE_STATE_GOING before calling going notifiers in error path
3. remove ftrace module notifier
4. remove livepatch module notifier

-- 
Josh