linux-kernel - Re: [PATCH v2 2/2] livepatch/module: remove livepatch module notifier

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Message-ID: <alpine.LNX.2.00.1602050958260.25516@pobox.suse.cz>
Date:	Fri, 5 Feb 2016 09:59:17 +0100 (CET)
From:	Miroslav Benes <mbenes@...e.cz>
To:	Josh Poimboeuf <jpoimboe@...hat.com>
cc:	Jessica Yu <jeyu@...hat.com>, Seth Jennings <sjenning@...hat.com>,
	Jiri Kosina <jikos@...nel.org>,
	Vojtech Pavlik <vojtech@...e.com>,
	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 v2 2/2] livepatch/module: remove livepatch module
 notifier

On Thu, 4 Feb 2016, Josh Poimboeuf wrote:

> On Mon, Feb 01, 2016 at 08:17:36PM -0500, Jessica Yu wrote:
> > Remove the livepatch module notifier in favor of directly enabling and
> > disabling patches to modules in the module loader. Hard-coding the
> > function calls ensures that ftrace_module_enable() is run before
> > klp_module_enable() during module load, and that klp_module_disable() is
> > run before ftrace_release_mod() during module unload. This way, ftrace
> > and livepatch code is run in the correct order during the module
> > load/unload sequence without dependence on the module notifier call chain.
> > 
> > This fixes a notifier ordering issue in which the ftrace module notifier
> > (and hence ftrace_module_enable()) for coming modules was being called
> > after klp_module_notify(), which caused livepatch modules to initialize
> > incorrectly.
> > 
> > Signed-off-by: Jessica Yu <jeyu@...hat.com>
> > ---
> >  include/linux/livepatch.h |   9 +++
> >  kernel/livepatch/core.c   | 144 ++++++++++++++++++++++------------------------
> >  kernel/module.c           |   8 +++
> >  3 files changed, 86 insertions(+), 75 deletions(-)
> > 
> > diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
> > index a882865..fdd5f1c 100644
> > --- a/include/linux/livepatch.h
> > +++ b/include/linux/livepatch.h
> > @@ -134,6 +134,15 @@ int klp_unregister_patch(struct klp_patch *);
> >  int klp_enable_patch(struct klp_patch *);
> >  int klp_disable_patch(struct klp_patch *);
> >  
> > +/* Called from the module loader during module coming/going states */
> > +extern int klp_module_enable(struct module *mod);
> > +extern void klp_module_disable(struct module *mod);
> > +
> > +#else /* !CONFIG_LIVEPATCH */
> > +
> > +static inline int klp_module_enable(struct module *mod) { return 0; }
> > +static inline void klp_module_disable(struct module *mod) { }
> > +
> >  #endif /* CONFIG_LIVEPATCH */
> >  
> >  #endif /* _LINUX_LIVEPATCH_H_ */
> > diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> > index bc2c85c..7aa975d 100644
> > --- a/kernel/livepatch/core.c
> > +++ b/kernel/livepatch/core.c
> > @@ -103,7 +103,7 @@ static void klp_find_object_module(struct klp_object *obj)
> >  	 */
> >  	mod = find_module(obj->name);
> >  	/*
> > -	 * Do not mess work of the module coming and going notifiers.
> > +	 * Do not mess work of the klp module coming and going handlers.
> >  	 * Note that the patch might still be needed before the going handler
> >  	 * is called. Module functions can be called even in the GOING state
> >  	 * until mod->exit() finishes. This is especially important for
> > @@ -866,103 +866,107 @@ int klp_register_patch(struct klp_patch *patch)
> >  }
> >  EXPORT_SYMBOL_GPL(klp_register_patch);
> >  
> > -static int klp_module_notify_coming(struct klp_patch *patch,
> > -				     struct klp_object *obj)
> > +/* Called when module state is MODULE_STATE_COMING */
> > +int klp_module_enable(struct module *mod)
> 
> I think this function name was originally my idea.  But now I'm thinking
> it could cause some confusion with the similarly named
> klp_enable_object().
> 
> How about naming it klp_module_coming()?  That more accurately describes
> its purpose IMO and it would also make the comment above it no longer
> necessary.
> 
> And similarly we could rename klp_module_disable() ->
> klp_module_going().

I agree. klp_module_{coming,going} is better.

Miroslav