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

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Message-ID: <20160204205511.GO22854@treble.redhat.com>
Date:	Thu, 4 Feb 2016 14:55:11 -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 v2 2/2] livepatch/module: remove livepatch module notifier

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().


-- 
Josh