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Message-ID: <20210105191755.GH17086@paulmck-ThinkPad-P72>
Date: Tue, 5 Jan 2021 11:17:55 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Dmitry Osipenko <digetx@...il.com>
Cc: Frederic Weisbecker <frederic@...nel.org>,
LKML <linux-kernel@...r.kernel.org>,
"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>,
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()
On Tue, Jan 05, 2021 at 09:10:30PM +0300, Dmitry Osipenko wrote:
> 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:
There is some ongoing discussion about what an overall proper fix might
look like, so in the meantime I am folding you changes below into
Frederic's original. ;-)
Thanx, Paul
> 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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