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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
Message-Id: <20220606050238.4162200-1-masahiroy@kernel.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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