linux-kernel - Re: [PATCH] clocksource: hyper-v: unexport __init-annotated hv_init

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Date:   Wed, 8 Jun 2022 12:27:34 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     "K . Y . Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        linux-hyperv@...r.kernel.org,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clocksource: hyper-v: unexport __init-annotated
 hv_init_clocksource()

On Mon, Jun 06, 2022 at 02:02:38PM +0900, Masahiro Yamada wrote:
> EXPORT_SYMBOL and __init is a bad combination because the .init.text
> section is freed up after the initialization. Hence, modules cannot
> use symbols annotated __init. The access to a freed symbol may end up
> with kernel panic.
> 
> modpost used to detect it, but it has been broken for a decade.
> 
> Recently, I fixed modpost so it started to warn it again, then this
> showed up in linux-next builds.
> 
> There are two ways to fix it:
> 
>   - Remove __init
>   - Remove EXPORT_SYMBOL
> 
> I chose the latter for this case because the only in-tree call-site,
> arch/x86/kernel/cpu/mshyperv.c is never compiled as modular.
> (CONFIG_HYPERVISOR_GUEST is boolean)
> 
> Fixes: dd2cb348613b ("clocksource/drivers: Continue making Hyper-V clocksource ISA agnostic")
> Reported-by: Stephen Rothwell <sfr@...b.auug.org.au>
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>

Applied to hyperv-fixes. Thanks.