[PATCH] clocksource: hyper-v: unexport __init-annotated hv_init_clocksource()

From: Masahiro Yamada <masahiroy@kernel.org>
To: "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
Cc: Masahiro Yamada <masahiroy@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: [PATCH] clocksource: hyper-v: unexport __init-annotated hv_init_clocksource()
Date: Mon,  6 Jun 2022 14:02:38 +0900	[thread overview]
Message-ID: <20220606050238.4162200-1-masahiroy@kernel.org> (raw)

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>
---

 drivers/clocksource/hyperv_timer.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c
index ff188ab68496..bb47610bbd1c 100644
--- a/drivers/clocksource/hyperv_timer.c
+++ b/drivers/clocksource/hyperv_timer.c
@@ -565,4 +565,3 @@ void __init hv_init_clocksource(void)
 	hv_sched_clock_offset = hv_read_reference_counter();
 	hv_setup_sched_clock(read_hv_sched_clock_msr);
 }
-EXPORT_SYMBOL_GPL(hv_init_clocksource);
-- 
2.32.0

