linux-kernel - Re: livepatch/module: remove livepatch module notifier

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Date:	Fri, 5 Feb 2016 11:06:56 +0100
From:	Petr Mladek <pmladek@...e.com>
To:	Miroslav Benes <mbenes@...e.cz>
Cc:	Jessica Yu <jeyu@...hat.com>, Josh Poimboeuf <jpoimboe@...hat.com>,
	Seth Jennings <sjenning@...hat.com>,
	Jiri Kosina <jikos@...nel.org>,
	Vojtech Pavlik <vojtech@...e.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>, live-patching@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: livepatch/module: remove livepatch module notifier

On Fri 2016-02-05 10:15:56, Miroslav Benes wrote:
> On Thu, 4 Feb 2016, Jessica Yu wrote:
> > Argh, thank you for catching that. I think we could split up
> > complete_formation()
> > into two functions in order to make the error handling work. 
> > 
> > Does all this look ok? 
> 
> Hm, there is an another option. We can cover the needed error handling in 
> complete_formation(). So for the first error there 
> (verify_export_symbols() fails) we need to only release module_mutex. For 
> our second error we need more. We would call module_bug_cleanup() under 
> module_mutex, module_disable_{ro,nx} and going notifiers. Is this correct? 
> It would be hidden in complete_formation() this way and cleaner in my 
> opinion. There is some code duplication though.

This sounds better to me.

> > Also, one last thing, I noticed that module->state
> > isn't
> > set to MODULE_STATE_GOING anywhere before the going notifier chain is called
> > in
> > the bug_cleanup label (I think it is still COMING at that point), so the
> > klp_module_disable call right afterwards would have bailed out because of
> > that.
> > To be consistent, shouldn't it be set before the going notifiers are called?
> 
> This could break something or introduce a race somewhere. Git grep says 
> there are several checks for MODULE_STATE_GOING through out the kernel 
> which need to be checked.

I think that we could relax the condition in the
klp_module_going/disable() function and allow to call it
also in MODULE_STATE_COMMING_STATE. It would deserve
a comment.

Best Regards,
Petr