linux-kernel - Re: PATCH v6 5/6] livepatch: Support separate list for replaced patches.

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Date:   Wed, 31 Jan 2018 17:19:11 +0100 (CET)
From:   Miroslav Benes <mbenes@...e.cz>
To:     Petr Mladek <pmladek@...e.com>
cc:     jpoimboe@...hat.com, jikos@...nel.org,
        Jason Baron <jbaron@...mai.com>, jeyu@...nel.org,
        Evgenii Shatokhin <eshatokhin@...tuozzo.com>,
        linux-kernel@...r.kernel.org, live-patching@...r.kernel.org
Subject: Re: PATCH v6 5/6] livepatch: Support separate list for replaced
 patches.

On Thu, 25 Jan 2018, Petr Mladek wrote:

> From: Jason Baron <jbaron@...mai.com>
> 
> We are going to add a feature called atomic replace. It will allow to
> create a patch that would replace all already registered patches.
> 
> The replaced patches will stay registered because they are typically
> unregistered by some package uninstall scripts. But we will remove
> these patches from @klp_patches list to keep the enabled patch
> on the bottom of the stack. Otherwise, we would need to implement
> rather complex logic for moving the patches on the stack. Also
> it would complicate implementation of the atomic replace feature.
> It is not worth it.
> 
> As a result, we will have patches that are registered but that
> are not longer usable. Let's get prepared for this and use
> a better descriptive name for klp_is_patch_registered() function.
> 
> Also create separate list for the replaced patches and allow to
> unregister them. Alternative solution would be to add a flag
> into struct klp_patch. Note that patch->kobj.state_initialized
> is not safe because it can be cleared outside klp_mutex.
> 
> This patch does not change the existing behavior.

Ok, why not. We could also unregister the patches right away and amend the 
check in klp_unregister_patch() not to return error. Ever.

However, this seems better in the end.

Miroslav