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Date:   Wed, 8 Jun 2022 12:27:34 +0000
From:   Wei Liu <wei.liu@kernel.org>
To:     Masahiro Yamada <masahiroy@kernel.org>
Cc:     "K . Y . Srinivasan" <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Wei Liu <wei.liu@kernel.org>, Dexuan Cui <decui@microsoft.com>,
        linux-hyperv@vger.kernel.org,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Michael Kelley <mikelley@microsoft.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] clocksource: hyper-v: unexport __init-annotated
 hv_init_clocksource()
Message-ID: <20220608122734.m25chzpwbr5ancnm@liuwe-devbox-debian-v2>
References: <20220606050238.4162200-1-masahiroy@kernel.org>
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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@canb.auug.org.au>
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Applied to hyperv-fixes. Thanks.