linux-kernel - Re: [PATCH v2 2/5] cpuidle: psci: Mark as PREEMPT

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Date:   Thu, 19 Jan 2023 16:40:30 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kevin Hilman <khilman@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Sudeep Holla <sudeep.holla@....com>, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Adrien Thierry <athierry@...hat.com>,
        Brian Masney <bmasney@...hat.com>,
        linux-rt-users@...r.kernel.org
Subject: Re: [PATCH v2 2/5] cpuidle: psci: Mark as PREEMPT_RT safe

On 17/01/2023 16:27, Ulf Hansson wrote:
> On Mon, 19 Dec 2022 at 16:15, Krzysztof Kozlowski
> <krzysztof.kozlowski@...aro.org> wrote:
>>
>> The PSCI cpuidle power domain in power_off callback uses
>> __this_cpu_write() so it is PREEMPT_RT safe.  This allows to use it in
>> Realtime kernels and solves errors like:
>>
>>   BUG: scheduling while atomic: swapper/2/0/0x00000002
>>   Hardware name: Qualcomm Technologies, Inc. Robotics RB5 (DT)
>>   Call trace:
>>    dump_backtrace.part.0+0xe0/0xf0
>>    show_stack+0x18/0x40
>>    dump_stack_lvl+0x68/0x84
>>    dump_stack+0x18/0x34
>>    __schedule_bug+0x60/0x80
>>    __schedule+0x628/0x800
>>    schedule_rtlock+0x28/0x5c
>>    rtlock_slowlock_locked+0x360/0xd30
>>    rt_spin_lock+0x88/0xb0
>>    genpd_lock_nested_spin+0x1c/0x30
>>    genpd_power_off.part.0.isra.0+0x20c/0x2a0
>>    genpd_runtime_suspend+0x150/0x2bc
>>    __rpm_callback+0x48/0x170
>>    rpm_callback+0x6c/0x7c
>>    rpm_suspend+0x108/0x660
>>    __pm_runtime_suspend+0x4c/0x8c
>>    __psci_enter_domain_idle_state.constprop.0+0x54/0xe0
>>    psci_enter_domain_idle_state+0x18/0x2c
>>    cpuidle_enter_state+0x8c/0x4e0
>>    cpuidle_enter+0x38/0x50
>>    do_idle+0x248/0x2f0
>>    cpu_startup_entry+0x24/0x30
>>    secondary_start_kernel+0x130/0x154
>>    __secondary_switched+0xb0/0xb4
>>
>> Cc: Adrien Thierry <athierry@...hat.com>
>> Cc: Brian Masney <bmasney@...hat.com>
>> Cc: linux-rt-users@...r.kernel.org
>> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
>> ---
>>  drivers/cpuidle/cpuidle-psci-domain.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/cpuidle/cpuidle-psci-domain.c b/drivers/cpuidle/cpuidle-psci-domain.c
>> index c80cf9ddabd8..d15a91fb7048 100644
>> --- a/drivers/cpuidle/cpuidle-psci-domain.c
>> +++ b/drivers/cpuidle/cpuidle-psci-domain.c
>> @@ -62,7 +62,8 @@ static int psci_pd_init(struct device_node *np, bool use_osi)
>>         if (!pd_provider)
>>                 goto free_pd;
>>
>> -       pd->flags |= GENPD_FLAG_IRQ_SAFE | GENPD_FLAG_CPU_DOMAIN;
>> +       pd->flags |= GENPD_FLAG_IRQ_SAFE | GENPD_FLAG_RT_SAFE | \
>> +                    GENPD_FLAG_CPU_DOMAIN;
> 
> My main concern with this, is that it will affect the parent domains
> too. Whether those would be able to use the GENPD_FLAG_RT_SAFE or not,
> is a different story.
> 
> In one way or the other, I think it would be better to limit the
> GENPD_FLAG_RT_SAFE to be used only for PREEMPT_RT kernels.

I can do it... or maybe we should just drop the flags (RT and IRQ safe)
when parent domain does not have it?

Best regards,
Krzysztof