linux-kernel - Re: [PATCH] livepatch: Fix the issue to make livepatch enable/disable patch correctly

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Message-ID: <20150722144004.GC23235@treble.redhat.com>
Date:	Wed, 22 Jul 2015 09:40:04 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Minfei Huang <mhuang@...hat.com>
Cc:	sjenning@...hat.com, jkosina@...e.cz, vojtech@...e.cz,
	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
	Minfei Huang <mnfhuang@...il.com>
Subject: Re: [PATCH] livepatch: Fix the issue to make livepatch
 enable/disable patch correctly

On Wed, Jul 15, 2015 at 04:55:06PM +0800, Minfei Huang wrote:
> From: Minfei Huang <mnfhuang@...il.com>
> 
> Livepatch will obey the stacking rule to enable/disable the patch. It
> only allows to enable the patch, when it is the fist disabled patch,
> disable the patch, when it is the last enabled patch.
> 
> In the livepatch code, it uses list to gather the all of the patches.
> And we do not know whether the previous/next patch is patched to the
> same modules or vmlinux in that way.
> 
> According to above rule, livepatch will make incorrect decision to
> enable/disable the patch. Following is an example to show how livepatch
> does.
> 
> - install the livepatch example module which is in samples/livepatch.
> - install the third part kernel module
> - install the livepatch module which is patched to the third part module
> - disable the livepatch example module
> 
> We can find that we can not disable livepatch example module, although
> it is the last enabled patch.
> 
> To fix this issue, we will find the corresponding patch which is patched
> to the same modules or vmlinux, when we enable/disable the patch.

Is it really safe to assume that there are no dependencies between
patches which patch different objects?

-- 
Josh
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