[PATCH] clocksource/arm_arch_timer: fix a lockdep warning

[Qian Cai]

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

This is due to the commit cb538267ea1e ("jump_label/lockdep: Assert we hold
the hotplug lock for _cpuslocked() operations"). Therefore, it will check
if it is really in the CPU hotplug path or not, and work around this
problem by using cpus_read_trylock(). The chance of not getting the read
lock is very small. If that happens, it will report a lockdep warning at
most.

Signed-off-by: Qian Cai <c...@gmx.us>
---
 drivers/clocksource/arm_arch_timer.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/clocksource/arm_arch_timer.c 
b/drivers/clocksource/arm_arch_timer.c
index 9a7d4dc..5c9acbd 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -497,11 +497,20 @@ void arch_timer_enable_workaround(const struct 
arch_timer_erratum_workaround *wa
                        per_cpu(timer_unstable_counter_workaround, i) = wa;
        }
 
+#ifdef CONFIG_HOTPLUG_CPU
+       i = 0;
+
        /*
         * Use the locked version, as we're called from the CPU
         * hotplug framework. Otherwise, we end-up in deadlock-land.
         */
+       i = cpus_read_trylock();
        static_branch_enable_cpuslocked(&arch_timer_read_ool_enabled);
+       if (i)
+               cpus_read_unlock();
+#else
+       static_branch_enable(&arch_timer_read_ool_enabled);
+#endif
 
        /*
         * Don't use the vdso fastpath if errata require using the
-- 
1.8.3.1