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Subject[PATCH v2] clocksource/arm_arch_timer: fix a lockdep warning
Date
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").

Since it is applying a global workaround to all CPUs here, it did not hold
any CPU locks in this path.

arch_timer_acpi_init
arch_timer_check_ool_workaround(ate_match_acpi_oem_info, table)
arch_timer_enable_workaround(wa, local = false)
for_each_possible_cpu()
per_cpu()

When hot-add a CPU, it will go with a slightly different route.

arch_timer_starting_cpu
__arch_timer_setup
arch_timer_check_ool_workaround(ate_match_local_cap_id, NULL)
arch_timer_enable_workaround(wa, local = true)
__this_cpu_write()

Hence, deal with them differently.

Fixes: 450f9689f294 (clocksource/arm_arch_timer: Use
static_branch_enable_cpuslocked())
Signed-off-by: Qian Cai <cai@gmx.us>
---

Changes since v1:
* Fixed the root cause instead of a workaround.

drivers/clocksource/arm_arch_timer.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index 9a7d4dc00b6e..81dca7d31d13 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -492,18 +492,21 @@ void arch_timer_enable_workaround(const struct arch_timer_erratum_workaround *wa

if (local) {
__this_cpu_write(timer_unstable_counter_workaround, wa);
+
+ /*
+ * Use the locked version, as we're called from the CPU
+ * hotplug framework. Otherwise, we end-up in
+ * deadlock-land.
+ */
+ static_branch_enable_cpuslocked(&arch_timer_read_ool_enabled);
} else {
for_each_possible_cpu(i)
per_cpu(timer_unstable_counter_workaround, i) = wa;
+ /* A global workaround is not on the CPU hotplug path. */
+ static_branch_enable(&arch_timer_read_ool_enabled);
}

/*
- * Use the locked version, as we're called from the CPU
- * hotplug framework. Otherwise, we end-up in deadlock-land.
- */
- static_branch_enable_cpuslocked(&arch_timer_read_ool_enabled);
-
- /*
* Don't use the vdso fastpath if errata require using the
* out-of-line counter accessor. We may change our mind pretty
* late in the game (with a per-CPU erratum, for example), so
--
1.8.3.1
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