linux-kernel - [PATCH 5.15 050/106] clocksource: hyper-v: unexport __init-annotated hv_init

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Message-Id: <20220620124725.870459142@linuxfoundation.org>
Date:   Mon, 20 Jun 2022 14:51:09 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Stephen Rothwell <sfr@...b.auug.org.au>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.15 050/106] clocksource: hyper-v: unexport __init-annotated hv_init_clocksource()

From: Masahiro Yamada <masahiroy@...nel.org>

[ Upstream commit 245b993d8f6c4e25f19191edfbd8080b645e12b1 ]

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>
Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>
Reviewed-by: Michael Kelley <mikelley@...rosoft.com>
Link: https://lore.kernel.org/r/20220606050238.4162200-1-masahiroy@kernel.org
Signed-off-by: Wei Liu <wei.liu@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.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);
-- 
2.35.1