From: Marc Zyngier <marc.zyngier@arm.com>
To: Qian Cai <cai@lca.pw>, akpm@linux-foundation.org
Cc: mark.rutland@arm.com, daniel.lezcano@linaro.org,
tglx@linutronix.de, peterz@infradead.org, mingo@kernel.org,
longman@redhat.com, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [RESEND PATCH v2] clocksource/arm_arch_timer: fix a lockdep warning
Date: Mon, 10 Dec 2018 14:48:03 +0000 [thread overview]
Message-ID: <68e11ecf-f0b3-6486-63af-c05086c947c3@arm.com> (raw)
In-Reply-To: <20181210135228.49751-1-cai@lca.pw>
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...
prev parent reply other threads:[~2018-12-10 14:48 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-03 22:45 [PATCH v2] clocksource/arm_arch_timer: fix a lockdep warning Qian Cai
2018-12-10 13:52 ` [RESEND PATCH " Qian Cai
2018-12-10 14:07 ` Peter Zijlstra
2018-12-10 14:19 ` Valentin Schneider
2018-12-10 14:47 ` Peter Zijlstra
2018-12-10 15:47 ` Qian Cai
2018-12-10 21:31 ` Thomas Gleixner
2018-12-14 15:05 ` Qian Cai
2018-12-10 14:48 ` Marc Zyngier [this message]
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