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Date: Tue, 5 Jan 2021 21:10:30 +0300
From: Dmitry Osipenko <digetx@...il.com>
To: Frederic Weisbecker <frederic@...nel.org>,
LKML <linux-kernel@...r.kernel.org>
Cc: "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>,
Fabio Estevam <festevam@...il.com>, stable@...r.kernel.org,
Thomas Gleixner <tglx@...utronix.de>,
"Paul E . McKenney" <paulmck@...nel.org>,
Len Brown <lenb@...nel.org>,
Pengutronix Kernel Team <kernel@...gutronix.de>,
NXP Linux Team <linux-imx@....com>,
Daniel Lezcano <daniel.lezcano@...aro.org>,
Shawn Guo <shawnguo@...nel.org>,
Sascha Hauer <s.hauer@...gutronix.de>,
"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH 2/4] cpuidle: Fix missing need_resched() check after
rcu_idle_enter()
05.01.2021 20:25, Dmitry Osipenko пишет:
> 22.12.2020 04:37, Frederic Weisbecker пишет:
>> Entering RCU idle mode may cause a deferred wake up of an RCU NOCB_GP
>> kthread (rcuog) to be serviced.
>>
>> Usually a wake up happening while running the idle task is spotted in
>> one of the need_resched() checks carefully placed within the idle loop
>> that can break to the scheduler.
>>
>> Unfortunately within cpuidle the call to rcu_idle_enter() is already
>> beyond the last generic need_resched() check. Some drivers may perform
>> their own checks like with mwait_idle_with_hints() but many others don't
>> and we may halt the CPU with a resched request unhandled, leaving the
>> task hanging.
>>
>> Fix this with performing a last minute need_resched() check after
>> calling rcu_idle_enter().
>>
>> Reported-by: Paul E. McKenney <paulmck@...nel.org>
>> Fixes: 1098582a0f6c (sched,idle,rcu: Push rcu_idle deeper into the idle path)
>> Cc: stable@...r.kernel.org
>> Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
>> Cc: Peter Zijlstra <peterz@...radead.org>
>> Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>> Cc: Thomas Gleixner <tglx@...utronix.de>
>> Cc: Ingo Molnar <mingo@...nel.org>
>> Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
>> ---
>> drivers/cpuidle/cpuidle.c | 33 +++++++++++++++++++++++++--------
>> 1 file changed, 25 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
>> index ef2ea1b12cd8..4cc1ba49ce05 100644
>> --- a/drivers/cpuidle/cpuidle.c
>> +++ b/drivers/cpuidle/cpuidle.c
>> @@ -134,8 +134,8 @@ int cpuidle_find_deepest_state(struct cpuidle_driver *drv,
>> }
>>
>> #ifdef CONFIG_SUSPEND
>> -static void enter_s2idle_proper(struct cpuidle_driver *drv,
>> - struct cpuidle_device *dev, int index)
>> +static int enter_s2idle_proper(struct cpuidle_driver *drv,
>> + struct cpuidle_device *dev, int index)
>> {
>> ktime_t time_start, time_end;
>> struct cpuidle_state *target_state = &drv->states[index];
>> @@ -151,7 +151,14 @@ static void enter_s2idle_proper(struct cpuidle_driver *drv,
>> stop_critical_timings();
>> if (!(target_state->flags & CPUIDLE_FLAG_RCU_IDLE))
>> rcu_idle_enter();
>> - target_state->enter_s2idle(dev, drv, index);
>> + /*
>> + * Last need_resched() check must come after rcu_idle_enter()
>> + * which may wake up RCU internal tasks.
>> + */
>> + if (!need_resched())
>> + target_state->enter_s2idle(dev, drv, index);
>> + else
>> + index = -EBUSY;
>> if (WARN_ON_ONCE(!irqs_disabled()))
>> local_irq_disable();
>> if (!(target_state->flags & CPUIDLE_FLAG_RCU_IDLE))
>> @@ -159,10 +166,13 @@ static void enter_s2idle_proper(struct cpuidle_driver *drv,
>> tick_unfreeze();
>> start_critical_timings();
>>
>> - time_end = ns_to_ktime(local_clock());
>> + if (index > 0) {
>
> index=0 is valid too
>
>> + time_end = ns_to_ktime(local_clock());
>> + dev->states_usage[index].s2idle_time += ktime_us_delta(time_end, time_start);
>> + dev->states_usage[index].s2idle_usage++;
>> + }
>>
>> - dev->states_usage[index].s2idle_time += ktime_us_delta(time_end, time_start);
>> - dev->states_usage[index].s2idle_usage++;
>> + return index;
>> }
>>
>> /**
>> @@ -184,7 +194,7 @@ int cpuidle_enter_s2idle(struct cpuidle_driver *drv, struct cpuidle_device *dev)
>> */
>> index = find_deepest_state(drv, dev, U64_MAX, 0, true);
>> if (index > 0) {
>> - enter_s2idle_proper(drv, dev, index);
>> + index = enter_s2idle_proper(drv, dev, index);
>> local_irq_enable();
>> }
>> return index;
>> @@ -234,7 +244,14 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv,
>> stop_critical_timings();
>> if (!(target_state->flags & CPUIDLE_FLAG_RCU_IDLE))
>> rcu_idle_enter();
>> - entered_state = target_state->enter(dev, drv, index);
>> + /*
>> + * Last need_resched() check must come after rcu_idle_enter()
>> + * which may wake up RCU internal tasks.
>> + */
>> + if (!need_resched())
>> + entered_state = target_state->enter(dev, drv, index);
>> + else
>> + entered_state = -EBUSY;
>> if (!(target_state->flags & CPUIDLE_FLAG_RCU_IDLE))
>> rcu_idle_exit();
>> start_critical_timings();
>>
>
> This patch causes a hardlock on NVIDIA Tegra using today's linux-next.
> Disabling coupled idling state helps. Please fix thanks in advance.
>
This isn't a proper fix, but it works:
diff --git a/drivers/cpuidle/cpuidle-tegra.c
b/drivers/cpuidle/cpuidle-tegra.c
index 191966dc8d02..ecc5d9b31553 100644
--- a/drivers/cpuidle/cpuidle-tegra.c
+++ b/drivers/cpuidle/cpuidle-tegra.c
@@ -148,7 +148,7 @@ static int tegra_cpuidle_c7_enter(void)
static int tegra_cpuidle_coupled_barrier(struct cpuidle_device *dev)
{
- if (tegra_pending_sgi()) {
+ if (tegra_pending_sgi() || need_resched()) {
/*
* CPU got local interrupt that will be lost after GIC's
* shutdown because GIC driver doesn't save/restore the
diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 4cc1ba49ce05..2bc52ccc339b 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -248,7 +248,7 @@ int cpuidle_enter_state(struct cpuidle_device *dev,
struct cpuidle_driver *drv,
* Last need_resched() check must come after rcu_idle_enter()
* which may wake up RCU internal tasks.
*/
- if (!need_resched())
+ if ((target_state->flags & CPUIDLE_FLAG_COUPLED) || !need_resched())
entered_state = target_state->enter(dev, drv, index);
else
entered_state = -EBUSY;
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