Realtime kernels are not supposed to go into deep sleep modes (neither
system nor CPUs) because the latencies might become unpredictable.
Therefore actual power suspending of CPU topology is not that important.
On the other hand, this runtime PM of CPU topology is not compatible
with PREEMPT_RT:
1. Core cpuidle path disables IRQs.
2. Core cpuidle calls cpuidle-psci.
3. cpuidle-psci in __psci_enter_domain_idle_state() calls
pm_runtime_put_sync_suspend() and pm_runtime_get_sync() which use
spinlocks (which are sleeping on PREEMPT_RT):
BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:46
in_atomic(): 1, irqs_disabled(): 128, non_block: 0, pid: 0, name: swapper/0
preempt_count: 1, expected: 0
RCU nest depth: 0, expected: 0
1 lock held by swapper/0/0:
#0: ffff20524613c1a0 (&dev->power.lock){+.+.}-{3:3}, at: __pm_runtime_suspend+0x30/0xac
irq event stamp: 18776
hardirqs last enabled at (18775): [<ffffa4853720ac80>] tick_nohz_idle_enter+0x7c/0x17c
hardirqs last disabled at (18776): [<ffffa4853717ae00>] do_idle+0xe0/0x300
softirqs last enabled at (4310): [<ffffa48537126398>] __local_bh_enable_ip+0x98/0x280
softirqs last disabled at (4288): [<ffffa4853721c250>] cgroup_idr_alloc.constprop.0+0x0/0xd0
Preemption disabled at:
[<ffffa485381e55a0>] schedule_preempt_disabled+0x20/0x30
CPU: 0 PID: 0 Comm: swapper/0 Tainted: G W 6.1.0-rt5-00322-gb49b67f1d8dc #1
Hardware name: Qualcomm Technologies, Inc. Robotics RB5 (DT)
Call trace:
dump_backtrace.part.0+0xe0/0xf0
show_stack+0x18/0x40
dump_stack_lvl+0x8c/0xb8
dump_stack+0x18/0x34
__might_resched+0x17c/0x214
rt_spin_lock+0x5c/0x100
__pm_runtime_suspend+0x30/0xac
__psci_enter_domain_idle_state.constprop.0+0x60/0x104
psci_enter_domain_idle_state+0x18/0x2c
cpuidle_enter_state+0x220/0x37c
cpuidle_enter+0x38/0x50
do_idle+0x258/0x300
cpu_startup_entry+0x28/0x30
rest_init+0x104/0x180
arch_post_acpi_subsys_init+0x0/0x18
start_kernel+0x6fc/0x73c
__primary_switched+0xbc/0xc4
Cc: Adrien Thierry <athierry@xxxxxxxxxx>
Cc: Brian Masney <bmasney@xxxxxxxxxx>
Cc: linux-rt-users@xxxxxxxxxxxxxxx
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
---
drivers/cpuidle/cpuidle-psci.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/cpuidle/cpuidle-psci.c b/drivers/cpuidle/cpuidle-psci.c
index 57bc3e3ae391..9d971cc4b12b 100644
--- a/drivers/cpuidle/cpuidle-psci.c
+++ b/drivers/cpuidle/cpuidle-psci.c
@@ -72,7 +72,7 @@ static int __psci_enter_domain_idle_state(struct cpuidle_device *dev,
ct_irq_enter_irqson();
if (s2idle)
dev_pm_genpd_suspend(pd_dev);
- else
+ else if (!IS_ENABLED(CONFIG_PREEMPT_RT))
pm_runtime_put_sync_suspend(pd_dev);
ct_irq_exit_irqson();
@@ -85,7 +85,7 @@ static int __psci_enter_domain_idle_state(struct cpuidle_device *dev,
ct_irq_enter_irqson();
if (s2idle)
dev_pm_genpd_resume(pd_dev);
- else
+ else if (!IS_ENABLED(CONFIG_PREEMPT_RT))
pm_runtime_get_sync(pd_dev);
ct_irq_exit_irqson();
--
2.34.1
