linux-kernel - Re: [PATCH v14 05/11] livepatch: Simplify API by removing registration step

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Date:   Thu, 13 Dec 2018 16:46:25 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Jiri Kosina <jikos@...nel.org>, Miroslav Benes <mbenes@...e.cz>,
        Jason Baron <jbaron@...mai.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Evgenii Shatokhin <eshatokhin@...tuozzo.com>,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v14 05/11] livepatch: Simplify API by removing
 registration step

On Thu, Nov 29, 2018 at 10:44:25AM +0100, Petr Mladek wrote:
> @@ -309,40 +297,33 @@ static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr,
>  
>  	mutex_lock(&klp_mutex);
>  
> -	if (!klp_is_patch_registered(patch)) {
> -		/*
> -		 * Module with the patch could either disappear meanwhile or is
> -		 * not properly initialized yet.
> -		 */
> -		ret = -EINVAL;
> -		goto err;
> -	}
> -
>  	if (patch->enabled == enabled) {
>  		/* already in requested state */
>  		ret = -EINVAL;
> -		goto err;
> +		goto out;
>  	}
>  
> -	if (patch == klp_transition_patch) {
> +	/*
> +	 * Allow to reverse a pending transition in both ways. It might be
> +	 * necessary to complete the transition without forcing and breaking
> +	 * the system integrity.
> +	 *
> +	 * Do not allow to re-enable a disabled patch because this interface
> +	 * is being destroyed.
> +	 */
> +	if (patch == klp_transition_patch)
>  		klp_reverse_transition();
> -	} else if (enabled) {
> -		ret = __klp_enable_patch(patch);
> -		if (ret)
> -			goto err;
> -	} else {
> +	else if (!enabled)
>  		ret = __klp_disable_patch(patch);
> -		if (ret)
> -			goto err;
> -	}
> +	else
> +		ret = -EINVAL;

Now that we can't re-enable a patch, I wonder if we really need both the
'patch->enabled' and 'klp_target_state' variables?

A patch is now always enabled, unless it's in transition, in which case
its 'enabled' state is the same as 'klp_target_state'.

For example I wonder if we could get rid of 'klp_target_state', since it
should be the same as 'klp_transition_patch->enabled'.

Or alternatively we could get rid of 'patch->enabled', since it should
be the same as

	patch == klp_transition_patch ? klp_target_state : true

Of course this could be a follow-on cleanup patch, which could be done
in the future, so as not to hold up the merging of these patches
anymore.

-- 
Josh