linux-kernel - Re: [PATCHv2 2/3] kernel: add support for live patching

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Message-ID: <20141119160540.GA2058@cerebellum.variantweb.net>
Date:	Wed, 19 Nov 2014 10:05:40 -0600
From:	Seth Jennings <sjenning@...hat.com>
To:	Miroslav Benes <mbenes@...e.cz>
Cc:	Josh Poimboeuf <jpoimboe@...hat.com>,
	Jiri Kosina <jkosina@...e.cz>,
	Vojtech Pavlik <vojtech@...e.cz>,
	Steven Rostedt <rostedt@...dmis.org>,
	Petr Mladek <pmladek@...e.cz>,
	Christoph Hellwig <hch@...radead.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	live-patching@...r.kernel.org, x86@...nel.org, kpatch@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2 2/3] kernel: add support for live patching

On Wed, Nov 19, 2014 at 04:27:39PM +0100, Miroslav Benes wrote:
> 
> Hi,
> 
> during rewriting our code I came across few more things. See below.
> 
> On Sun, 16 Nov 2014, Seth Jennings wrote:
> 
> [...]
> 
> > +/******************************
> > + * module notifier
> > + *****************************/
> > +
> > +static void lpc_module_notify_coming(struct module *pmod,
> > +				     struct lpc_object *obj)
> > +{
> > +	struct module *mod = obj->mod;
> > +	int ret;
> > +
> > +	pr_notice("applying patch '%s' to loading module '%s'\n",
> > +		  mod->name, pmod->name);
> 
> This looks strange. I guess the arguments should be swapped.

Indeed, you are correct :)

> 
> > +	obj->mod = mod;
> 
> And this is redundant.

True again!

> 
> > +	ret = lpc_enable_object(pmod, obj);
> > +	if (ret)
> > +		pr_warn("failed to apply patch '%s' to module '%s' (%d)\n",
> > +			pmod->name, mod->name, ret);
> > +}
> > +
> > +static void lpc_module_notify_going(struct module *pmod,
> > +				    struct lpc_object *obj)
> > +{
> > +	struct module *mod = obj->mod;
> > +	int ret;
> > +
> > +	pr_notice("reverting patch '%s' on unloading module '%s'\n",
> > +		  pmod->name, mod->name);
> > +	ret = lpc_disable_object(obj);
> > +	if (ret)
> > +		pr_warn("failed to revert patch '%s' on module '%s' (%d)\n",
> > +			pmod->name, mod->name, ret);
> > +	obj->mod = NULL;
> > +}
> > +
> > +static int lpc_module_notify(struct notifier_block *nb, unsigned long action,
> > +			    void *data)
> > +{
> > +	struct module *mod = data;
> > +	struct lpc_patch *patch;
> > +	struct lpc_object *obj;
> > +
> > +	mutex_lock(&lpc_mutex);
> > +
> > +	if (action != MODULE_STATE_COMING && action != MODULE_STATE_GOING)
> > +		goto out;
> > +
> > +	list_for_each_entry(patch, &lpc_patches, list) {
> > +		if (patch->state == LPC_DISABLED)
> > +			continue;
> > +		list_for_each_entry(obj, &patch->objs, list) {
> > +			if (strcmp(obj->name, mod->name))
> > +				continue;
> > +			if (action == MODULE_STATE_COMING) {
> > +				obj->mod = mod;
> > +				lpc_module_notify_coming(patch->mod, obj);
> > +			} else /* MODULE_STATE_GOING */
> > +				lpc_module_notify_going(patch->mod, obj);
> > +			break;
> > +		}
> > +	}
> > +out:
> > +	mutex_unlock(&lpc_mutex);
> > +	return 0;
> > +}
> 
> [...]
> 
> > +static struct lpc_object *lpc_create_object(struct kobject *root,
> > +					    struct lp_object *userobj)
> > +{
> > +	struct lpc_object *obj;
> > +	int ret;
> > +
> > +	/* alloc */
> > +	obj = kzalloc(sizeof(*obj), GFP_KERNEL);
> > +	if (!obj)
> > +		return NULL;
> > +
> > +	/* init */
> > +	INIT_LIST_HEAD(&obj->list);
> > +	obj->name = userobj->name;
> > +	obj->relocs = userobj->relocs;
> > +	obj->state = LPC_DISABLED;
> > +	/* obj->mod set by lpc_object_module_get() */
> > +	INIT_LIST_HEAD(&obj->funcs);
> 
> There is nothing like lpc_object_module_get() in the code. Did you mean 
> lpc_find_object_module()?

Yes, this comment should be removed or updated.

Thanks,
Seth

> 
> Thank you,
> --
> Miroslav Benes
> SUSE Labs
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