linux-kernel - Re: [PATCH v3] livepatch: Prevent to apply the patch once coming module notifier fails

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Message-ID: <20150513141415.GB28284@treble.redhat.com>
Date:	Wed, 13 May 2015 09:14:15 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Minfei Huang <mnfhuang@...il.com>
Cc:	mbenes@...e.cz, sjenning@...hat.com, jkosina@...e.cz,
	vojtech@...e.cz, live-patching@...r.kernel.org,
	linux-kernel@...r.kernel.org, mhuang@...hat.com
Subject: Re: [PATCH v3] livepatch: Prevent to apply the patch once coming
 module notifier fails

On Tue, May 12, 2015 at 10:04:44PM +0800, Minfei Huang wrote:
> @@ -883,7 +883,7 @@ int klp_register_patch(struct klp_patch *patch)
>  }
>  EXPORT_SYMBOL_GPL(klp_register_patch);
>  
> -static void klp_module_notify_coming(struct klp_patch *patch,
> +static int klp_module_notify_coming(struct klp_patch *patch,
>  				     struct klp_object *obj)
>  {
>  	struct module *pmod = patch->mod;
> @@ -891,22 +891,24 @@ static void klp_module_notify_coming(struct klp_patch *patch,
>  	int ret;
>  
>  	ret = klp_init_object_loaded(patch, obj);
> -	if (ret)
> -		goto err;
> +	if (ret) {
> +		pr_warn("failed to initialize the patch '%s' (%d)\n",
> +				pmod->name, ret);
> +		goto out;
> +	}

Can you change it to:

"failed to initialize the patch '%s' for module '%s' (%d)\n" ?

That would make it more consistent with the other error message and
identify the failing module.

Also, the indentation should be fixed on the second pr_warn() line.

>  
>  	if (patch->state == KLP_DISABLED)
> -		return;
> +		goto out;
>  
>  	pr_notice("applying patch '%s' to loading module '%s'\n",
>  		  pmod->name, mod->name);
>  
>  	ret = klp_enable_object(obj);
> -	if (!ret)
> -		return;
> -
> -err:
> -	pr_warn("failed to apply patch '%s' to module '%s' (%d)\n",
> -		pmod->name, mod->name, ret);
> +	if (ret)
> +		pr_warn("failed to apply patch '%s' to module '%s' (%d)\n",
> +				pmod->name, mod->name, ret);

Bad indentation here too.

> @@ -930,6 +932,7 @@ disabled:
>  static int klp_module_notify(struct notifier_block *nb, unsigned long action,
>  			     void *data)
>  {
> +	int ret;
>  	struct module *mod = data;
>  	struct klp_patch *patch;
>  	struct klp_object *obj;
> @@ -955,7 +958,13 @@ static int klp_module_notify(struct notifier_block *nb, unsigned long action,
>  
>  			if (action == MODULE_STATE_COMING) {
>  				obj->mod = mod;
> -				klp_module_notify_coming(patch, obj);
> +				ret = klp_module_notify_coming(patch, obj);
> +				if (ret) {
> +					obj->mod = NULL;
> +					pr_warn("patch '%s' is dead, remove it "
> +						"or re-install the module '%s'\n",
> +						patch->mod->name, obj->name);
> +				}

The patch isn't necessarily dead, since it might also include previously
enabled changes for vmlinux or other modules.  It can actually be a
dangerous condition if there's a mismatch between old code in the module
and new code elsewhere.  How about something like:

"patch '%s' is in an inconsistent state!\n"

Also, there's no need to split up the string literal into two lines.
It's ok for a line to have more than 80 columns in that case.

-- 
Josh
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