linux-kernel - Re: [PATCHv3 2/3] kernel: add support for live patching

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Message-ID: <20141121161308.GA11339@cerebellum.variantweb.net>
Date:	Fri, 21 Nov 2014 10:13:08 -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: [PATCHv3 2/3] kernel: add support for live patching

On Fri, Nov 21, 2014 at 04:46:32PM +0100, Miroslav Benes wrote:
> On Fri, 21 Nov 2014, Josh Poimboeuf wrote:
> 
> > On Fri, Nov 21, 2014 at 03:44:35PM +0100, Miroslav Benes wrote:
> > > On Fri, 21 Nov 2014, Jiri Kosina wrote:
> > > 
> > > [...]
> > > 
> > > > [ ... snip ... ]
> > > > > +static int klp_init_patch(struct klp_patch *patch)
> > > > > +{
> > > > > +	int ret;
> > > > > +
> > > > > +	mutex_lock(&klp_mutex);
> > > > > +
> > > > > +	/* init */
> > > > > +	patch->state = LPC_DISABLED;
> > > > > +
> > > > > +	/* sysfs */
> > > > > +	ret = kobject_init_and_add(&patch->kobj, &klp_ktype_patch,
> > > > > +				   klp_root_kobj, patch->mod->name);
> > > > > +	if (ret)
> > > > > +		return ret;
> > > > 
> > > > klp_mutex is leaked locked here.
> > > > 
> > > > > +
> > > > > +	/* create objects */
> > > > > +	ret = klp_init_objects(patch);
> > > > > +	if (ret) {
> > > > > +		kobject_put(&patch->kobj);
> > > > > +		return ret;
> > > > 
> > > > And here as well.
> > > > 
> > > > All in all, this is looking very good to me. I think we are really close 
> > > > to having a code that all the parties would agree with. Thanks everybody,
> > > 
> > > The leaking is my fault. I missed that somehow during rebasing.
> > > 
> > > Seth, could you please fix it in v4? 
> > 
> > Is it necessary to grab the mutex at the beginning of klp_init_patch?  I
> > think we only need it when adding it to the global list at the end of
> > the function.
> 
> I think it's not necessary now after thinking about that. It could happen 
> that init values could be written twice to some patch structure if 
> klp_register_patch would be called twice. But it should not corrupt 
> anything and adding to the global list is protected. However I think we 
> should define what is protected by klp_mutex and comment it somewhere near 
> the mutex definition (if only the klp_patches list is protected or 
> something more (in the future)).

I'll fix it up for v4, moving the mutex just around the list_add() and
adding a comment about what is protected by the mutex.

Seth

> 
> Mira
> --
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