Messages in this thread | | | Subject | Re: [RESEND PATCH v2] clocksource/arm_arch_timer: fix a lockdep warning | From | Marc Zyngier <> | Date | Mon, 10 Dec 2018 14:48:03 +0000 |
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On 10/12/2018 13:52, 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 > > 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() > > There is also another path did not have any CPU lock. > > time_init > clocksource_probe > arch_timer_of_init > arch_timer_check_ool_workaround(ate_match_dt, np) > arch_timer_enable_workaround(wa, local = false) > > When hot-adding 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@lca.pw> > --- > > v2: fix 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 > @@ -492,17 +492,20 @@ 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);
I have the ugly feeling that it breaks the (equally ugly) big-little stuff where the boot CPU is affected. In this context, you'd end-up without the lock being taken and you'll get the same splat.
We could start testing the CPU number, but Peter's approach seem much more palatable to me.
Thanks,
M. -- Jazz is not dead. It just smells funny...
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