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

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Date:   Mon, 10 Dec 2018 15:07:03 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Qian Cai <cai@....pw>
Cc:     akpm@...ux-foundation.org, mark.rutland@....com,
        marc.zyngier@....com, daniel.lezcano@...aro.org,
        tglx@...utronix.de, 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, 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);
 }