linux-kernel - Re: [PATCH] livepatch: Enhance livepatch to support remove patch module dynamically

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Message-ID: <alpine.LNX.2.00.1504011534240.843@pobox.suse.cz>
Date:	Wed, 1 Apr 2015 15:35:46 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Minfei Huang <minfei.huang@...oo.com>
cc:	jpoimboe@...hat.com, sjenning@...hat.com,
	Vojtech Pavlik <vojtech@...e.cz>,
	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] livepatch: Enhance livepatch to support remove patch
 module dynamically

On Wed, 1 Apr 2015, Minfei Huang wrote:

> As mentioned in the annotation, the patch module would not permit to
> be removed once it is loaded.
> 
> Kernel may crash in the case that the function in the patch module is
> called during removing.
> 
> We will increase the module reference when the patch module is enable,
> so that the module cannt be removed. Once the module is disable, it will
> be removed.
> 
> Signed-off-by: Minfei Huang <minfei.huang@...oo.com>
> ---
>  kernel/livepatch/core.c | 47 +++++++++++++++++++++++++++++++----------------
>  1 file changed, 31 insertions(+), 16 deletions(-)
> 
> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> index 3f9f1d6..0266950 100644
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -502,6 +502,17 @@ static int __klp_disable_patch(struct klp_patch *patch)
>  	return 0;
>  }
>  
> +static int __klp_disable_patch_nolock(struct klp_patch *patch)
> +{
> +	int ret = 0;
> +
> +	ret = __klp_disable_patch(patch);
> +	if (ret)
> +		return ret;
> +	module_put(patch->mod);
> +	return ret;
> +}
> +

Your patch doesn't solve the problem at all.

There is no guarantee that once __klp_disable_patch() returns noone is 
using the old code any more.

-- 
Jiri Kosina
SUSE Labs
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