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

[Vitaly Kuznetsov]

Masahiro Yamada <masahiroy@xxxxxxxxxx> writes:

> 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@xxxxxxxxxxxxxxxx>
> Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
> ---
>
>  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);

hv_init_clocksource() is not called from modules indeed, 

Reviewed-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>

-- 
Vitaly