linux-kernel - Re: [RFC PATCH] livepatch/module: Do not patch modules that are not ready

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Date:	Tue, 3 Mar 2015 13:35:39 -0600
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Petr Mladek <pmladek@...e.cz>
Cc:	Seth Jennings <sjenning@...hat.com>, Jiri Kosina <jkosina@...e.cz>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Miroslav Benes <mbenes@...e.cz>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	mingo@...nel.org, mathieu.desnoyers@...icios.com, oleg@...hat.com,
	paulmck@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	andi@...stfloor.org, rostedt@...dmis.org, tglx@...utronix.de
Subject: Re: [RFC PATCH] livepatch/module: Do not patch modules that are not
 ready

On Tue, Mar 03, 2015 at 01:31:28PM -0600, Josh Poimboeuf wrote:
> @@ -89,16 +89,29 @@ static bool klp_is_object_loaded(struct klp_object *obj)
>  /* sets obj->mod if object is not vmlinux and module is found */
>  static void klp_find_object_module(struct klp_object *obj)
>  {
> -	if (!klp_is_module(obj))
> +	struct module *mod;
> +
> +	if (!klp_is_module(obj) || obj->mod)
>  		return;
>  
>  	mutex_lock(&module_mutex);
> +
>  	/*
>  	 * We don't need to take a reference on the module here because we have
>  	 * the klp_mutex, which is also taken by the module notifier.  This
>  	 * prevents any module from unloading until we release the klp_mutex.
>  	 */
> -	obj->mod = find_module(obj->name);
> +	mod = find_module(obj->name);
> +
> +	/*
> +	 * MODULE_STATE_COMING means we got to the module first before the
> +	 * notifier did.  ftrace is already initialized, so it's fine to go
> +	 * ahead and start using it.
> +	 */

This comment should probably be improved to say:

"MODULE_STATE_COMING and !obj->mod means..."

--
Josh
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