linux-kernel - Re: [PATCH 3/3] static_call: Fix static_call

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Date:   Mon, 22 Mar 2021 14:07:54 +0100
From:   Jessica Yu <jeyu@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>, x86@...nel.org,
        jbaron@...mai.com, ardb@...nel.org, linux-kernel@...r.kernel.org,
        sumit.garg@...aro.org, oliver.sang@...el.com, jarkko@...nel.org
Subject: Re: [PATCH 3/3] static_call: Fix static_call_update() sanity check

+++ Steven Rostedt [19/03/21 14:00 -0400]:
>On Fri, 19 Mar 2021 13:57:38 +0100
>Peter Zijlstra <peterz@...radead.org> wrote:
>
>> Jessica, can you explain how !MODULE_UNLOAD is supposed to work?
>> Alternatives, jump_labels and static_call all can have relocations into
>> __exit code. Not loading it at all would be BAD.
>
>According to the description:
>
>" Without this option you will not be able to unload any
>  modules (note that some modules may not be unloadable anyway), which
>  makes your kernel smaller, faster and simpler.
>  If unsure, say Y."
>
>Seems there's no reason to load the "exit" portion, as that's what makes it
>"smaller".

Exactly. If you disable MODULE_UNLOAD, then you don't intend to ever
unload any modules, and so you'll never end up calling the module's
cleanup/exit function. That code would basically be never used, so
that's why it's not loaded in the first place.