linux-kernel - Re: [PATCH v3] livepatch: Don't block removal of patches that are safe to unload

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Message-ID: <YjH6W6eL1XQAGcxD@alley>
Date:   Wed, 16 Mar 2022 15:55:23 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Chengming Zhou <zhouchengming@...edance.com>
Cc:     jpoimboe@...hat.com, jikos@...nel.org, mbenes@...e.cz,
        joe.lawrence@...hat.com, live-patching@...r.kernel.org,
        linux-kernel@...r.kernel.org, songmuchun@...edance.com,
        qirui.001@...edance.com
Subject: Re: [PATCH v3] livepatch: Don't block removal of patches that are
 safe to unload

On Sat 2022-03-12 23:22:20, Chengming Zhou wrote:
> module_put() is not called for a patch with "forced" flag. It should
> block the removal of the livepatch module when the code might still
> be in use after forced transition.
> 
> klp_force_transition() currently sets "forced" flag for all patches on
> the list.
> 
> In fact, any patch can be safely unloaded when it passed through
> the consistency model in KLP_UNPATCHED transition.
> 
> By other words, the "forced" flag must be set only for livepatches
> that are being removed. In particular, set the "forced" flag:
> 
>   + only for klp_transition_patch when the transition to KLP_UNPATCHED
>     state was forced.
> 
>   + all replaced patches when the transition to KLP_PATCHED state was
>     forced and the patch was replacing the existing patches.
> 
> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>

Looks reasonable, passes livepatch tests:

Reviewed-by: Petr Mladek <pmladek@...e.com>
Tested-by: Petr Mladek <pmladek@...e.com>

Just let me repeat. The "force" flags must be used carefully because
it breaks the consistency model.

Best Regards,
Petr