linux-kernel - Re: [PATCH v14 10/11] livepatch: Remove ordering and refuse loading conflicting patches

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Message-ID: <alpine.LSU.2.21.1812051126550.31935@pobox.suse.cz>
Date:   Wed, 5 Dec 2018 11:27:22 +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 10/11] livepatch: Remove ordering and refuse loading
 conflicting patches

On Thu, 29 Nov 2018, Petr Mladek wrote:

> The atomic replace and cumulative patches were introduced as a more secure
> way to handle dependent patches. They simplify the logic:
> 
>   + Any new cumulative patch is supposed to take over shadow variables
>     and changes made by callbacks from previous livepatches.
> 
>   + All replaced patches are discarded and the modules can be unloaded.
>     As a result, there is only one scenario when a cumulative livepatch
>     gets disabled.
> 
> The different handling of "normal" and cumulative patches might cause
> confusion. It would make sense to keep only one mode. On the other hand,
> it would be rude to enforce using the cumulative livepatches even for
> trivial and independent (hot) fixes.
> 
> This patch removes the stack of patches. The list of enabled patches
> is still needed but the ordering is not longer enforced.
> 
> Note that it is not possible to catch all possible dependencies. It is
> the responsibility of the livepatch authors to decide.
> 
> Nevertheless this patch prevents having two patches for the same function
> enabled at the same time after the transition finishes. It might help
> to catch obvious mistakes. But more importantly, we do not need to
> handle situation when a patch in the middle of the function stack
> (ops->func_stack) is being removed.
> 
> Signed-off-by: Petr Mladek <pmladek@...e.com>

Acked-by: Miroslav Benes <mbenes@...e.cz>

M