With Paul, we've been thinking that the idle loop wasn't twisted enough
yet to deserve 2020.
rcutorture, after some recent parameter changes, has been complaining
about a hung task.
It appears that rcu_idle_enter() may wake up a NOCB kthread but this
happens after the last generic need_resched() check. Some cpuidle drivers
fix it by chance but many others don't.
Here is a proposed bunch of fixes. I will need to also fix the
rcu_user_enter() case, likely using irq_work, since nohz_full requires
irq work to support self IPI.
Also more generally, this raise the question of local task wake_up()
under disabled interrupts. When a wake up occurs in a preempt disabled
section, it gets handled by the outer preempt_enable() call. There is no
similar mechanism when a wake up occurs with interrupts disabled. I guess
it is assumed to be handled, at worst, in the next tick. But a local irq
work would provide instant preemption once IRQs are re-enabled. Of course
this would only make sense in CONFIG_PREEMPTION, and when the tick is
disabled...
git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
sched/idle
HEAD: f2fa6e4a070c1535b9edc9ee097167fd2b15d235
Thanks,
Frederic
---
Frederic Weisbecker (4):
sched/idle: Fix missing need_resched() check after rcu_idle_enter()
cpuidle: Fix missing need_resched() check after rcu_idle_enter()
ARM: imx6q: Fix missing need_resched() check after rcu_idle_enter()
ACPI: processor: Fix missing need_resched() check after rcu_idle_enter()
arch/arm/mach-imx/cpuidle-imx6q.c | 7 ++++++-
drivers/acpi/processor_idle.c | 10 ++++++++--
drivers/cpuidle/cpuidle.c | 33 +++++++++++++++++++++++++--------
kernel/sched/idle.c | 18 ++++++++++++------
4 files changed, 51 insertions(+), 17 deletions(-)
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 <[email protected]>
Fixes: 1098582a0f6c (sched,idle,rcu: Push rcu_idle deeper into the idle path)
Cc: [email protected]
Cc: Daniel Lezcano <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Rafael J. Wysocki <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Signed-off-by: Frederic Weisbecker <[email protected]>
---
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) {
+ 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();
--
2.25.1
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 in default_idle_call(), the call to rcu_idle_enter() is
already beyond the last need_resched() check 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 <[email protected]>
Fixes: 96d3fd0d315a (rcu: Break call_rcu() deadlock involving scheduler and perf)
Cc: [email protected]
Cc: Peter Zijlstra <[email protected]>
Cc: Rafael J. Wysocki <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar<[email protected]>
Signed-off-by: Frederic Weisbecker <[email protected]>
---
kernel/sched/idle.c | 18 ++++++++++++------
1 file changed, 12 insertions(+), 6 deletions(-)
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 305727ea0677..1af60dc50beb 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -109,15 +109,21 @@ void __cpuidle default_idle_call(void)
rcu_idle_enter();
lockdep_hardirqs_on(_THIS_IP_);
- arch_cpu_idle();
+ /*
+ * Last need_resched() check must come after rcu_idle_enter()
+ * which may wake up RCU internal tasks.
+ */
+ if (!need_resched()) {
+ arch_cpu_idle();
+ raw_local_irq_disable();
+ }
/*
- * OK, so IRQs are enabled here, but RCU needs them disabled to
- * turn itself back on.. funny thing is that disabling IRQs
- * will cause tracing, which needs RCU. Jump through hoops to
- * make it 'work'.
+ * OK, so IRQs are enabled after arch_cpu_idle(), but RCU needs
+ * them disabled to turn itself back on.. funny thing is that
+ * disabling IRQs will cause tracing, which needs RCU. Jump through
+ * hoops to make it 'work'.
*/
- raw_local_irq_disable();
lockdep_hardirqs_off(_THIS_IP_);
rcu_idle_exit();
lockdep_hardirqs_on(_THIS_IP_);
--
2.25.1
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 acpi_idle_enter_bm() the call to rcu_idle_enter()
is already beyond the last generic need_resched() check. The cpu idle
implementation happens to be ok because it ends up calling
mwait_idle_with_hints() or acpi_safe_halt() which both perform their own
need_resched() checks. But the suspend to idle implementation doesn't so
it may suspend 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 <[email protected]>
Fixes: 1fecfdbb7acc (ACPI: processor: Take over RCU-idle for C3-BM idle)
Cc: [email protected]
Cc: Len Brown <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Rafael J. Wysocki <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar<[email protected]>
Signed-off-by: Frederic Weisbecker <[email protected]>
---
drivers/acpi/processor_idle.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index d93e400940a3..c4939c49d972 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -604,8 +604,14 @@ static int acpi_idle_enter_bm(struct cpuidle_driver *drv,
}
rcu_idle_enter();
-
- acpi_idle_do_entry(cx);
+ /*
+ * Last need_resched() check must come after rcu_idle_enter()
+ * which may wake up RCU internal tasks. mwait_idle_with_hints()
+ * and acpi_safe_halt() have their own checks but s2idle
+ * implementation doesn't.
+ */
+ if (!need_resched())
+ acpi_idle_do_entry(cx);
rcu_idle_exit();
--
2.25.1
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 imx6q_enter_wait() is beyond the last generic
need_resched() check and it performs a wfi right away after the call to
rcu_idle_enter(). 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 <[email protected]>
Fixes: 1a67b9263e06 (ARM: imx6q: Fixup RCU usage for cpuidle)
Cc: [email protected]
Cc: Shawn Guo <[email protected]>
Cc: Sascha Hauer <[email protected]>
Cc: Pengutronix Kernel Team <[email protected]>
Cc: Fabio Estevam <[email protected]>
Cc: NXP Linux Team <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Rafael J. Wysocki <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Signed-off-by: Frederic Weisbecker <[email protected]>
---
arch/arm/mach-imx/cpuidle-imx6q.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/arch/arm/mach-imx/cpuidle-imx6q.c b/arch/arm/mach-imx/cpuidle-imx6q.c
index 094337dc1bc7..31a60d257d3d 100644
--- a/arch/arm/mach-imx/cpuidle-imx6q.c
+++ b/arch/arm/mach-imx/cpuidle-imx6q.c
@@ -25,7 +25,12 @@ static int imx6q_enter_wait(struct cpuidle_device *dev,
raw_spin_unlock(&cpuidle_lock);
rcu_idle_enter();
- cpu_do_idle();
+ /*
+ * Last need_resched() check must come after rcu_idle_enter()
+ * which may wake up RCU internal tasks.
+ */
+ if (!need_resched())
+ cpu_do_idle();
rcu_idle_exit();
raw_spin_lock(&cpuidle_lock);
--
2.25.1
On Tue, Dec 22, 2020 at 02:37:09AM +0100, Frederic Weisbecker wrote:
> 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 in default_idle_call(), the call to rcu_idle_enter() is
> already beyond the last need_resched() check 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 <[email protected]>
> Fixes: 96d3fd0d315a (rcu: Break call_rcu() deadlock involving scheduler and perf)
> Cc: [email protected]
> Cc: Peter Zijlstra <[email protected]>
> Cc: Rafael J. Wysocki <[email protected]>
> Cc: Thomas Gleixner <[email protected]>
> Cc: Ingo Molnar<[email protected]>
> Signed-off-by: Frederic Weisbecker <[email protected]>
Tested-by: Paul E. McKenney <[email protected]>
> ---
> kernel/sched/idle.c | 18 ++++++++++++------
> 1 file changed, 12 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
> index 305727ea0677..1af60dc50beb 100644
> --- a/kernel/sched/idle.c
> +++ b/kernel/sched/idle.c
> @@ -109,15 +109,21 @@ void __cpuidle default_idle_call(void)
> rcu_idle_enter();
> lockdep_hardirqs_on(_THIS_IP_);
>
> - arch_cpu_idle();
> + /*
> + * Last need_resched() check must come after rcu_idle_enter()
> + * which may wake up RCU internal tasks.
> + */
> + if (!need_resched()) {
> + arch_cpu_idle();
> + raw_local_irq_disable();
> + }
>
> /*
> - * OK, so IRQs are enabled here, but RCU needs them disabled to
> - * turn itself back on.. funny thing is that disabling IRQs
> - * will cause tracing, which needs RCU. Jump through hoops to
> - * make it 'work'.
> + * OK, so IRQs are enabled after arch_cpu_idle(), but RCU needs
> + * them disabled to turn itself back on.. funny thing is that
> + * disabling IRQs will cause tracing, which needs RCU. Jump through
> + * hoops to make it 'work'.
> */
> - raw_local_irq_disable();
> lockdep_hardirqs_off(_THIS_IP_);
> rcu_idle_exit();
> lockdep_hardirqs_on(_THIS_IP_);
> --
> 2.25.1
>
On 12/22/2020 2:37 AM, Frederic Weisbecker wrote:
> With Paul, we've been thinking that the idle loop wasn't twisted enough
> yet to deserve 2020.
>
> rcutorture, after some recent parameter changes, has been complaining
> about a hung task.
>
> It appears that rcu_idle_enter() may wake up a NOCB kthread but this
> happens after the last generic need_resched() check. Some cpuidle drivers
> fix it by chance but many others don't.
>
> Here is a proposed bunch of fixes. I will need to also fix the
> rcu_user_enter() case, likely using irq_work, since nohz_full requires
> irq work to support self IPI.
>
> Also more generally, this raise the question of local task wake_up()
> under disabled interrupts. When a wake up occurs in a preempt disabled
> section, it gets handled by the outer preempt_enable() call. There is no
> similar mechanism when a wake up occurs with interrupts disabled. I guess
> it is assumed to be handled, at worst, in the next tick. But a local irq
> work would provide instant preemption once IRQs are re-enabled. Of course
> this would only make sense in CONFIG_PREEMPTION, and when the tick is
> disabled...
>
> git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
> sched/idle
>
> HEAD: f2fa6e4a070c1535b9edc9ee097167fd2b15d235
>
> Thanks,
> Frederic
> ---
>
> Frederic Weisbecker (4):
> sched/idle: Fix missing need_resched() check after rcu_idle_enter()
> cpuidle: Fix missing need_resched() check after rcu_idle_enter()
> ARM: imx6q: Fix missing need_resched() check after rcu_idle_enter()
> ACPI: processor: Fix missing need_resched() check after rcu_idle_enter()
>
>
> arch/arm/mach-imx/cpuidle-imx6q.c | 7 ++++++-
> drivers/acpi/processor_idle.c | 10 ++++++++--
> drivers/cpuidle/cpuidle.c | 33 +++++++++++++++++++++++++--------
> kernel/sched/idle.c | 18 ++++++++++++------
> 4 files changed, 51 insertions(+), 17 deletions(-)
Please feel free to add
Reviewed-by: Rafael J. Wysocki <[email protected]>
to all patches in the series.
Thanks!
On Tue, Dec 22, 2020 at 05:19:51PM +0100, Rafael J. Wysocki wrote:
> On 12/22/2020 2:37 AM, Frederic Weisbecker wrote:
> > With Paul, we've been thinking that the idle loop wasn't twisted enough
> > yet to deserve 2020.
> >
> > rcutorture, after some recent parameter changes, has been complaining
> > about a hung task.
> >
> > It appears that rcu_idle_enter() may wake up a NOCB kthread but this
> > happens after the last generic need_resched() check. Some cpuidle drivers
> > fix it by chance but many others don't.
> >
> > Here is a proposed bunch of fixes. I will need to also fix the
> > rcu_user_enter() case, likely using irq_work, since nohz_full requires
> > irq work to support self IPI.
> >
> > Also more generally, this raise the question of local task wake_up()
> > under disabled interrupts. When a wake up occurs in a preempt disabled
> > section, it gets handled by the outer preempt_enable() call. There is no
> > similar mechanism when a wake up occurs with interrupts disabled. I guess
> > it is assumed to be handled, at worst, in the next tick. But a local irq
> > work would provide instant preemption once IRQs are re-enabled. Of course
> > this would only make sense in CONFIG_PREEMPTION, and when the tick is
> > disabled...
> >
> > git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
> > sched/idle
> >
> > HEAD: f2fa6e4a070c1535b9edc9ee097167fd2b15d235
> >
> > Thanks,
> > Frederic
> > ---
> >
> > Frederic Weisbecker (4):
> > sched/idle: Fix missing need_resched() check after rcu_idle_enter()
> > cpuidle: Fix missing need_resched() check after rcu_idle_enter()
> > ARM: imx6q: Fix missing need_resched() check after rcu_idle_enter()
> > ACPI: processor: Fix missing need_resched() check after rcu_idle_enter()
> >
> >
> > arch/arm/mach-imx/cpuidle-imx6q.c | 7 ++++++-
> > drivers/acpi/processor_idle.c | 10 ++++++++--
> > drivers/cpuidle/cpuidle.c | 33 +++++++++++++++++++++++++--------
> > kernel/sched/idle.c | 18 ++++++++++++------
> > 4 files changed, 51 insertions(+), 17 deletions(-)
>
> Please feel free to add
>
> Reviewed-by: Rafael J. Wysocki <[email protected]>
>
> to all patches in the series.
I would guess that they will take some other path to mainline, but I have
queued these to cut down on rcutorture's whining. ;-)
Thanx, Paul
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 <[email protected]>
> Fixes: 1098582a0f6c (sched,idle,rcu: Push rcu_idle deeper into the idle path)
> Cc: [email protected]
> Cc: Daniel Lezcano <[email protected]>
> Cc: Peter Zijlstra <[email protected]>
> Cc: Rafael J. Wysocki <[email protected]>
> Cc: Thomas Gleixner <[email protected]>
> Cc: Ingo Molnar <[email protected]>
> Signed-off-by: Frederic Weisbecker <[email protected]>
> ---
> 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.
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 <[email protected]>
>> Fixes: 1098582a0f6c (sched,idle,rcu: Push rcu_idle deeper into the idle path)
>> Cc: [email protected]
>> Cc: Daniel Lezcano <[email protected]>
>> Cc: Peter Zijlstra <[email protected]>
>> Cc: Rafael J. Wysocki <[email protected]>
>> Cc: Thomas Gleixner <[email protected]>
>> Cc: Ingo Molnar <[email protected]>
>> Signed-off-by: Frederic Weisbecker <[email protected]>
>> ---
>> 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;
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 <[email protected]>
> >> Fixes: 1098582a0f6c (sched,idle,rcu: Push rcu_idle deeper into the idle path)
> >> Cc: [email protected]
> >> Cc: Daniel Lezcano <[email protected]>
> >> Cc: Peter Zijlstra <[email protected]>
> >> Cc: Rafael J. Wysocki <[email protected]>
> >> Cc: Thomas Gleixner <[email protected]>
> >> Cc: Ingo Molnar <[email protected]>
> >> Signed-off-by: Frederic Weisbecker <[email protected]>
> >> ---
> >> 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;
>