linux-kernel - Re: [RESEND PATCH v2] clocksource/arm_arch

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Date:   Mon, 10 Dec 2018 22:31:21 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     Qian Cai <cai@....pw>, akpm@...ux-foundation.org,
        mark.rutland@....com, marc.zyngier@....com,
        daniel.lezcano@...aro.org, mingo@...nel.org, longman@...hat.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH v2] clocksource/arm_arch_timer: fix a lockdep
 warning

On Mon, 10 Dec 2018, Peter Zijlstra wrote:
> On Mon, Dec 10, 2018 at 08:52:28AM -0500, Qian Cai wrote:
> > Booting this Huawei TaiShan 2280 arm64 server generated this lockdep
> > warning.
> > 
> > [    0.000000]  lockdep_assert_cpus_held+0x50/0x60
> > [    0.000000]  static_key_enable_cpuslocked+0x30/0xe8
> > [    0.000000]  arch_timer_check_ool_workaround+0x128/0x2d0
> > [    0.000000]  arch_timer_acpi_init+0x274/0x6ac
> > [    0.000000]  acpi_table_parse+0x1ac/0x218
> > [    0.000000]  __acpi_probe_device_table+0x164/0x1ec
> > [    0.000000]  timer_probe+0x1bc/0x254
> > [    0.000000]  time_init+0x44/0x98
> > [    0.000000]  start_kernel+0x4ec/0x7d4
> 
> It seems to me we want something like:
> 
> ---
>  kernel/cpu.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 91d5c38eb7e5..e1ee8caf28b5 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -313,6 +313,8 @@ void cpus_write_unlock(void)
>  
>  void lockdep_assert_cpus_held(void)
>  {
> +	if (system_state < SYSTEM_RUNNING)
> +		return;
>  	percpu_rwsem_assert_held(&cpu_hotplug_lock);
>  }
 
Hmm, no. SYSTEM_SCHEDULING is what you want because RUNNING is set way too
late.

Thanks,

	tglx