linux-kernel - Re: [PATCH v4] livepatch/module: Correctly handle coming and going modules

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Message-ID: <20150312192303.GA32376@treble.redhat.com>
Date:	Thu, 12 Mar 2015 14:23:03 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Petr Mladek <pmladek@...e.cz>
Cc:	Seth Jennings <sjenning@...hat.com>, Jiri Kosina <jkosina@...e.cz>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Miroslav Benes <mbenes@...e.cz>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	mingo@...nel.org, mathieu.desnoyers@...icios.com, oleg@...hat.com,
	paulmck@...ux.vnet.ibm.com, live-patching@...r.kernel.org,
	linux-kernel@...r.kernel.org, andi@...stfloor.org,
	rostedt@...dmis.org, tglx@...utronix.de
Subject: Re: [PATCH v4] livepatch/module: Correctly handle coming and going
 modules

On Thu, Mar 12, 2015 at 12:55:13PM +0100, Petr Mladek wrote:
> There is a notifier that handles live patches for coming and going modules.
> It takes klp_mutex lock to avoid races with coming and going patches but
> it does not keep the lock all the time. Therefore the following races are
> possible:
> 
>   1. The notifier is called sometime in STATE_MODULE_COMING. The module
>      is visible by find_module() in this state all the time. It means that
>      new patch can be registered and enabled even before the notifier is
>      called. It might create wrong order of stacked patches, see below
>      for an example.
> 
>    2. New patch could still see the module in the GOING state even after
>       the notifier has been called. It will try to initialize the related
>       object structures but the module could disappear at any time. There
>       will stay mess in the structures. It might even cause an invalid
>       memory access.
> 
> This patch solves the problem by adding a boolean variable into struct module.
> The value is true after the coming and before the going handler is called.
> New patches need to be applied when the value is true and they need to ignore
> the module when the value is false.

Acked-by: Josh Poimboeuf <jpoimboe@...hat.com>
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