linux-kernel - Re: [PATCH] module: treat exit sections the same as init sections when !CONFIG_MODULE

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Message-ID: <YFoAtV58k+1zgH50@hirez.programming.kicks-ass.net>
Date:   Tue, 23 Mar 2021 15:52:37 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Jessica Yu <jeyu@...nel.org>
Cc:     x86@...nel.org, rostedt@...dmis.org, jpoimboe@...hat.com,
        jbaron@...mai.com, ardb@...nel.org, sumit.garg@...aro.org,
        oliver.sang@...el.com, jarkko@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] module: treat exit sections the same as init sections
 when !CONFIG_MODULE_UNLOAD

On Tue, Mar 23, 2021 at 03:27:56PM +0100, Jessica Yu wrote:
> Dynamic code patching (alternatives, jump_label and static_call) can
> have sites in __exit code, even if __exit is never executed. Therefore
> __exit must be present at runtime, at least for as long as __init code
> is.
> 
> Additionally, for jump_label and static_call, the __exit sites must also
> identify as within_module_init(), such that the infrastructure is aware
> to never touch them after module init -- alternatives are only ran once
> at init and hence don't have this particular constraint.
> 
> By making __exit identify as __init for !MODULE_UNLOAD, the above is
> satisfied.
> 
> So the section ordering should look like the following when
> !CONFIG_MODULE_UNLOAD, with the .exit sections moved to the init region of
> the module.
> 
> Core section allocation order:
>  	.text
>  	.rodata
>  	__ksymtab_gpl
>  	__ksymtab_strings
>  	.note.* sections
>  	.bss
>  	.data
>  	.gnu.linkonce.this_module
>  Init section allocation order:
>  	.init.text
>  	.exit.text
>  	.symtab
>  	.strtab
> 
> [jeyu: thanks to Peter Zijlstra for most of the changelog]
> 
> Link: https://lore.kernel.org/lkml/YFiuphGw0RKehWsQ@gunter/
> Signed-off-by: Jessica Yu <jeyu@...nel.org>

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>

> ---
> 
> Do you want to take this patch with the other static_call patches? Or
> should I take this through modules-next?

Take it through modules-next, I haven't seen an actual report on this
and it's been broken forever afaict. I only found it by accident while
chasing this other problem.