linux-kernel - Re: [RFC PATCH 8/9] livepatch: allow patch modules to be removed

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Date:	Fri, 13 Feb 2015 06:44:12 -0600
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Miroslav Benes <mbenes@...e.cz>
Cc:	Jiri Slaby <jslaby@...e.cz>, Seth Jennings <sjenning@...hat.com>,
	Jiri Kosina <jkosina@...e.cz>,
	Vojtech Pavlik <vojtech@...e.cz>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 8/9] livepatch: allow patch modules to be removed

On Thu, Feb 12, 2015 at 04:22:24PM +0100, Miroslav Benes wrote:
> On Tue, 10 Feb 2015, Jiri Slaby wrote:
> 
> > On 02/09/2015, 06:31 PM, Josh Poimboeuf wrote:
> > > --- a/kernel/livepatch/core.c
> > > +++ b/kernel/livepatch/core.c
> > ...
> > > @@ -497,10 +500,6 @@ static struct attribute *klp_patch_attrs[] = {
> > >  
> > >  static void klp_kobj_release_patch(struct kobject *kobj)
> > >  {
> > > -	/*
> > > -	 * Once we have a consistency model we'll need to module_put() the
> > > -	 * patch module here.  See klp_register_patch() for more details.
> > > -	 */
> > 
> > I deliberately let you write the note in there :). What happens when I
> > leave some attribute in /sys open and you remove the module in the meantime?
> 
> And if that attribute is <enabled> it can lead even to the deadlock. You 
> can try it yourself with the patchset applied and lockdep on. Simple 
> series of insmod, disable and rmmod of the patch.
> 
> Just for the sake of completeness...

Ouch, thanks.

-- 
Josh
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