Re: [PATCH v3 00/51] cpuidle,rcu: Clean up the mess

[Peter Zijlstra <peterz@infradead.org>]

On Mon, Jan 16, 2023 at 04:59:04PM +0000, Mark Rutland wrote:

> I'm sorry to have to bear some bad news on that front. :(

Moo, something had to give..


> IIUC what's happenign here is the PSCI cpuidle driver has entered idle and RCU
> is no longer watching when arm64's cpu_suspend() manipulates DAIF. Our
> local_daif_*() helpers poke lockdep and tracing, hence the call to
> trace_hardirqs_off() and the RCU usage.

Right, strictly speaking not needed at this point, IRQs should have been
traced off a long time ago.

> I think we need RCU to be watching all the way down to cpu_suspend(), and it's
> cpu_suspend() that should actually enter/exit idle context. That and we need to
> make cpu_suspend() and the low-level PSCI invocation noinstr.
> 
> I'm not sure whether 32-bit will have a similar issue or not.

I'm not seeing 32bit or Risc-V have similar issues here, but who knows,
maybe I missed somsething.

In any case, the below ought to cure the ARM64 case and remove that last
known RCU_NONIDLE() user as a bonus.

---
diff --git a/arch/arm64/kernel/cpuidle.c b/arch/arm64/kernel/cpuidle.c
index 41974a1a229a..42e19fff40ee 100644
--- a/arch/arm64/kernel/cpuidle.c
+++ b/arch/arm64/kernel/cpuidle.c
@@ -67,10 +67,10 @@ __cpuidle int acpi_processor_ffh_lpi_enter(struct acpi_lpi_state *lpi)
 	u32 state = lpi->address;
 
 	if (ARM64_LPI_IS_RETENTION_STATE(lpi->arch_flags))
-		return CPU_PM_CPU_IDLE_ENTER_RETENTION_PARAM(psci_cpu_suspend_enter,
+		return CPU_PM_CPU_IDLE_ENTER_RETENTION_PARAM_RCU(psci_cpu_suspend_enter,
 						lpi->index, state);
 	else
-		return CPU_PM_CPU_IDLE_ENTER_PARAM(psci_cpu_suspend_enter,
+		return CPU_PM_CPU_IDLE_ENTER_PARAM_RCU(psci_cpu_suspend_enter,
 					     lpi->index, state);
 }
 #endif
diff --git a/arch/arm64/kernel/suspend.c b/arch/arm64/kernel/suspend.c
index e7163f31f716..0fbdf5fe64d8 100644
--- a/arch/arm64/kernel/suspend.c
+++ b/arch/arm64/kernel/suspend.c
@@ -4,6 +4,7 @@
 #include <linux/slab.h>
 #include <linux/uaccess.h>
 #include <linux/pgtable.h>
+#include <linux/cpuidle.h>
 #include <asm/alternative.h>
 #include <asm/cacheflush.h>
 #include <asm/cpufeature.h>
@@ -104,6 +105,10 @@ int cpu_suspend(unsigned long arg, int (*fn)(unsigned long))
 	 * From this point debug exceptions are disabled to prevent
 	 * updates to mdscr register (saved and restored along with
 	 * general purpose registers) from kernel debuggers.
+	 *
+	 * Strictly speaking the trace_hardirqs_off() here is superfluous,
+	 * hardirqs should be firmly off by now. This really ought to use
+	 * something like raw_local_daif_save().
 	 */
 	flags = local_daif_save();
 
@@ -120,6 +125,8 @@ int cpu_suspend(unsigned long arg, int (*fn)(unsigned long))
 	 */
 	arm_cpuidle_save_irq_context(&context);
 
+	ct_cpuidle_enter();
+
 	if (__cpu_suspend_enter(&state)) {
 		/* Call the suspend finisher */
 		ret = fn(arg);
@@ -133,8 +140,11 @@ int cpu_suspend(unsigned long arg, int (*fn)(unsigned long))
 		 */
 		if (!ret)
 			ret = -EOPNOTSUPP;
+
+		ct_cpuidle_exit();
 	} else {
-		RCU_NONIDLE(__cpu_suspend_exit());
+		ct_cpuidle_exit();
+		__cpu_suspend_exit();
 	}
 
 	arm_cpuidle_restore_irq_context(&context);
diff --git a/drivers/cpuidle/cpuidle-psci.c b/drivers/cpuidle/cpuidle-psci.c
index 4fc4e0381944..312a34ef28dc 100644
--- a/drivers/cpuidle/cpuidle-psci.c
+++ b/drivers/cpuidle/cpuidle-psci.c
@@ -69,16 +69,12 @@ static __cpuidle int __psci_enter_domain_idle_state(struct cpuidle_device *dev,
 	else
 		pm_runtime_put_sync_suspend(pd_dev);
 
-	ct_cpuidle_enter();
-
 	state = psci_get_domain_state();
 	if (!state)
 		state = states[idx];
 
 	ret = psci_cpu_suspend_enter(state) ? -1 : idx;
 
-	ct_cpuidle_exit();
-
 	if (s2idle)
 		dev_pm_genpd_resume(pd_dev);
 	else
@@ -192,7 +188,7 @@ static __cpuidle int psci_enter_idle_state(struct cpuidle_device *dev,
 {
 	u32 *state = __this_cpu_read(psci_cpuidle_data.psci_states);
 
-	return CPU_PM_CPU_IDLE_ENTER_PARAM(psci_cpu_suspend_enter, idx, state[idx]);
+	return CPU_PM_CPU_IDLE_ENTER_PARAM_RCU(psci_cpu_suspend_enter, idx, state[idx]);
 }
 
 static const struct of_device_id psci_idle_state_match[] = {
diff --git a/drivers/firmware/psci/psci.c b/drivers/firmware/psci/psci.c
index e7bcfca4159f..f3a044fa4652 100644
--- a/drivers/firmware/psci/psci.c
+++ b/drivers/firmware/psci/psci.c
@@ -462,11 +462,22 @@ int psci_cpu_suspend_enter(u32 state)
 	if (!psci_power_state_loses_context(state)) {
 		struct arm_cpuidle_irq_context context;
 
+		ct_cpuidle_enter();
 		arm_cpuidle_save_irq_context(&context);
 		ret = psci_ops.cpu_suspend(state, 0);
 		arm_cpuidle_restore_irq_context(&context);
+		ct_cpuidle_exit();
 	} else {
+		/*
+		 * ARM64 cpu_suspend() wants to do ct_cpuidle_*() itself.
+		 */
+		if (!IS_ENABLED(CONFIG_ARM64))
+			ct_cpuidle_enter();
+
 		ret = cpu_suspend(state, psci_suspend_finisher);
+
+		if (!IS_ENABLED(CONFIG_ARM64))
+			ct_cpuidle_exit();
 	}
 
 	return ret;
diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
index 630c879143c7..3183aeb7f5b4 100644
--- a/include/linux/cpuidle.h
+++ b/include/linux/cpuidle.h
@@ -307,7 +307,7 @@ extern s64 cpuidle_governor_latency_req(unsigned int cpu);
 #define __CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter,			\
 				idx,					\
 				state,					\
-				is_retention)				\
+				is_retention, is_rcu)			\
 ({									\
 	int __ret = 0;							\
 									\
@@ -319,9 +319,11 @@ extern s64 cpuidle_governor_latency_req(unsigned int cpu);
 	if (!is_retention)						\
 		__ret =  cpu_pm_enter();				\
 	if (!__ret) {							\
-		ct_cpuidle_enter();					\
+		if (!is_rcu)						\
+			ct_cpuidle_enter();				\
 		__ret = low_level_idle_enter(state);			\
-		ct_cpuidle_exit();					\
+		if (!is_rcu)						\
+			ct_cpuidle_exit();				\
 		if (!is_retention)					\
 			cpu_pm_exit();					\
 	}								\
@@ -330,15 +332,21 @@ extern s64 cpuidle_governor_latency_req(unsigned int cpu);
 })
 
 #define CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx)	\
-	__CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, idx, 0)
+	__CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, idx, 0, 0)
 
 #define CPU_PM_CPU_IDLE_ENTER_RETENTION(low_level_idle_enter, idx)	\
-	__CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, idx, 1)
+	__CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, idx, 1, 0)
 
 #define CPU_PM_CPU_IDLE_ENTER_PARAM(low_level_idle_enter, idx, state)	\
-	__CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, state, 0)
+	__CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, state, 0, 0)
+
+#define CPU_PM_CPU_IDLE_ENTER_PARAM_RCU(low_level_idle_enter, idx, state)	\
+	__CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, state, 0, 1)
 
 #define CPU_PM_CPU_IDLE_ENTER_RETENTION_PARAM(low_level_idle_enter, idx, state)	\
-	__CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, state, 1)
+	__CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, state, 1, 0)
+
+#define CPU_PM_CPU_IDLE_ENTER_RETENTION_PARAM_RCU(low_level_idle_enter, idx, state)	\
+	__CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, state, 1, 1)
 
 #endif /* _LINUX_CPUIDLE_H */