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

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Date:	Thu, 4 Feb 2016 18:29:46 +0100 (CET)
From:	Miroslav Benes <mbenes@...e.cz>
To:	Jessica Yu <jeyu@...hat.com>
cc:	Josh Poimboeuf <jpoimboe@...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 Mon, 1 Feb 2016, Jessica Yu wrote:

> +/* 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);

We do not use 'extern' keyword in header files. It is redundant. 
Unfortunately, the situation differs among header files and it is hard to 
be consistent.

> +	/*
> +	 * Each module has to know that the coming handler has
> +	 * been called. We never know what module will get
> +	 * patched by a new patch.
> +	 */
> +	mod->klp_alive = true;

This comment should fixed too.

Note: we still need klp_alive, because the race is still there even 
without notifiers.

> +void klp_module_disable(struct module *mod)
>  {
> -	int ret;
> -	struct module *mod = data;
>  	struct klp_patch *patch;
>  	struct klp_object *obj;
>  
> -	if (action != MODULE_STATE_COMING && action != MODULE_STATE_GOING)
> -		return 0;
> +	if (mod->state != MODULE_STATE_GOING)
> +		return;

This is similar to what Petr proposed. We must be in MODULE_STATE_GOING 
here. We could WARN here and return.

> diff --git a/kernel/module.c b/kernel/module.c
> index b05d466..71c77ed 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -3375,6 +3378,10 @@ static int complete_formation(struct module *mod, struct load_info *info)
>  	mutex_unlock(&module_mutex);
>  
>  	ftrace_module_enable(mod);
> +	err = klp_module_enable(mod);
> +	if (err)
> +		goto out;
> +

if (err)
	return err;

module_mutex is already unlocked so no need to jump to out.

Apart from these minor things and Petr's remarks it looks ok.

Thanks for fixing this.
Miroslav