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

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Message-ID: <YFikbJfytBSqBPDU@hirez.programming.kicks-ass.net>
Date:   Mon, 22 Mar 2021 15:06:36 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Jessica Yu <jeyu@...nel.org>
Cc:     Steven Rostedt <rostedt@...dmis.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

On Mon, Mar 22, 2021 at 02:07:54PM +0100, Jessica Yu wrote:
> +++ 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.

As explained, that's broken. Has always been for as long as we've had
alternatives.