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

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Date:	Mon, 18 May 2015 14:08:06 +0200
From:	Petr Mladek <pmladek@...e.cz>
To:	Josh Poimboeuf <jpoimboe@...hat.com>
Cc:	Minfei Huang <mnfhuang@...il.com>, 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 Wed 2015-05-13 09:14:15, Josh Poimboeuf wrote:
> 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"

It must not be dangerous, otherwise the patch could not get applied
immediately.

I would omit this message completely. It would just duplicate the
warning printed by klp_module_notify_coming().


> 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.

I suggest to run ./scripts/chechpatch.pl before you send any patch.
It would catch the indentation problems, split of the string, ...

Best Regards,
Petr
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