linux-kernel - Re: [PATCH v14 04/11] livepatch: Refuse to unload only livepatches available during a forced transition

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Date:   Mon, 3 Dec 2018 16:29:32 +0100 (CET)
From:   Miroslav Benes <mbenes@...e.cz>
To:     Petr Mladek <pmladek@...e.com>
cc:     Jiri Kosina <jikos@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        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 04/11] livepatch: Refuse to unload only livepatches
 available during a forced transition

You probably forgot to replace the subject with Josh's proposal.

> module_put() is currently never called in klp_complete_transition() when
> klp_force is set. As a result, we might keep the reference count even when
> klp_enable_patch() fails and klp_cancel_transition() is called.

Correct.

> This might make an assumption that a module might get blocked in some
> strange init state. Fortunately, it is not the case. The reference count
> is ignored when mod->init fails and erroneous modules are always removed.

I do not understand the paragraph and its connection to the problem (and I don't
remember if I understood it previously or not and forgot to mention it).

> Anyway, this might make some confusion. Instead, this patch moves
> the global klp_forced flag into struct klp_patch. As a result,
> we block only modules that might still be in use after a forced
> transition. Newly loaded livepatches might be eventually completely
> removed later.

It makes sense by itself only.

> It is not a big deal. But the code is at least consistent with
> the reality.
> 
> Signed-off-by: Petr Mladek <pmladek@...e.com>


> @@ -633,5 +632,7 @@ void klp_force_transition(void)
>  	for_each_possible_cpu(cpu)
>  		klp_update_patch_state(idle_task(cpu));
>  
> -	klp_forced = true;
> +	/* Refuse unloading all livepatches. The code might be in use. */
> +	list_for_each_entry(patch, &klp_patches, list)
> +		patch->forced = true;

Is the comment necessary? If yes, I'd change it to something similar to the new
subject.

Thanks,
Miroslav