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Subject[patch V2 61/67] rcu: Convert rcutree to hotplug state machine
From: Thomas Gleixner <tglx@linutronix.de>

Straight forward conversion to the state machine. Though the question arises
whether this needs really all these state transitions to work.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
---
include/linux/cpuhotplug.h | 3 +
include/linux/rcutiny.h | 7 +++
include/linux/rcutree.h | 7 +++
kernel/cpu.c | 14 ++++++
kernel/rcu/tree.c | 105 ++++++++++++++++++++++-----------------------
5 files changed, 83 insertions(+), 53 deletions(-)

--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -21,11 +21,13 @@ enum cpuhp_state {
CPUHP_X2APIC_PREPARE,
CPUHP_SMPCFD_PREPARE,
CPUHP_TIMERS_DEAD,
+ CPUHP_RCUTREE_PREP,
CPUHP_NOTIFY_PREPARE,
CPUHP_BRINGUP_CPU,
CPUHP_AP_IDLE_DEAD,
CPUHP_AP_OFFLINE,
CPUHP_AP_SCHED_STARTING,
+ CPUHP_AP_RCUTREE_DYING,
CPUHP_AP_IRQ_GIC_STARTING,
CPUHP_AP_IRQ_GICV3_STARTING,
CPUHP_AP_IRQ_HIP04_STARTING,
@@ -81,6 +83,7 @@ enum cpuhp_state {
CPUHP_AP_PERF_ARM_CCI_ONLINE,
CPUHP_AP_PERF_ARM_CCN_ONLINE,
CPUHP_AP_WORKQUEUE_ONLINE,
+ CPUHP_AP_RCUTREE_ONLINE,
CPUHP_AP_NOTIFY_ONLINE,
CPUHP_AP_ONLINE_DYN,
CPUHP_AP_ONLINE_DYN_END = CPUHP_AP_ONLINE_DYN + 30,
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -243,4 +243,11 @@ static inline void rcu_all_qs(void)
barrier(); /* Avoid RCU read-side critical sections leaking across. */
}

+/* RCUtree hotplug events */
+#define rcutree_prepare_cpu NULL
+#define rcutree_online_cpu NULL
+#define rcutree_offline_cpu NULL
+#define rcutree_dead_cpu NULL
+#define rcutree_dying_cpu NULL
+
#endif /* __LINUX_RCUTINY_H */
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -111,4 +111,11 @@ bool rcu_is_watching(void);

void rcu_all_qs(void);

+/* RCUtree hotplug events */
+int rcutree_prepare_cpu(unsigned int cpu);
+int rcutree_online_cpu(unsigned int cpu);
+int rcutree_offline_cpu(unsigned int cpu);
+int rcutree_dead_cpu(unsigned int cpu);
+int rcutree_dying_cpu(unsigned int cpu);
+
#endif /* __LINUX_RCUTREE_H */
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1205,6 +1205,11 @@ static struct cpuhp_step cpuhp_bp_states
.startup = NULL,
.teardown = timers_dead_cpu,
},
+ [CPUHP_RCUTREE_PREP] = {
+ .name = "RCU-tree prepare",
+ .startup = rcutree_prepare_cpu,
+ .teardown = rcutree_dead_cpu,
+ },
/*
* Preparatory and dead notifiers. Will be replaced once the notifiers
* are converted to states.
@@ -1261,6 +1266,10 @@ static struct cpuhp_step cpuhp_ap_states
.startup = sched_cpu_starting,
.teardown = sched_cpu_dying,
},
+ [CPUHP_AP_RCUTREE_DYING] = {
+ .startup = NULL,
+ .teardown = rcutree_dying_cpu,
+ },
/*
* Low level startup/teardown notifiers. Run with interrupts
* disabled. Will be removed once the notifiers are converted to
@@ -1294,6 +1303,11 @@ static struct cpuhp_step cpuhp_ap_states
.startup = workqueue_online_cpu,
.teardown = workqueue_offline_cpu,
},
+ [CPUHP_AP_RCUTREE_ONLINE] = {
+ .name = "RCU-tree online",
+ .startup = rcutree_online_cpu,
+ .teardown = rcutree_offline_cpu,
+ },

/*
* Online/down_prepare notifiers. Will be removed once the notifiers
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1073,11 +1073,11 @@ EXPORT_SYMBOL_GPL(rcu_is_watching);
* offline to continue to use RCU for one jiffy after marking itself
* offline in the cpu_online_mask. This leniency is necessary given the
* non-atomic nature of the online and offline processing, for example,
- * the fact that a CPU enters the scheduler after completing the CPU_DYING
- * notifiers.
+ * the fact that a CPU enters the scheduler after completing the teardown
+ * of the CPU.
*
- * This is also why RCU internally marks CPUs online during the
- * CPU_UP_PREPARE phase and offline during the CPU_DEAD phase.
+ * This is also why RCU internally marks CPUs online during in the
+ * preparation phase and offline after the CPU has been taken down.
*
* Disable checking if in an NMI handler because we cannot safely report
* errors from NMI handlers anyway.
@@ -3806,12 +3806,58 @@ rcu_init_percpu_data(int cpu, struct rcu
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}

-static void rcu_prepare_cpu(int cpu)
+int rcutree_prepare_cpu(unsigned int cpu)
{
struct rcu_state *rsp;

for_each_rcu_flavor(rsp)
rcu_init_percpu_data(cpu, rsp);
+
+ rcu_prepare_kthreads(cpu);
+ rcu_spawn_all_nocb_kthreads(cpu);
+
+ return 0;
+}
+
+static void rcutree_affinity_setting(unsigned int cpu, int outgoing)
+{
+ struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
+
+ rcu_boost_kthread_setaffinity(rdp->mynode, outgoing);
+}
+
+int rcutree_online_cpu(unsigned int cpu)
+{
+ sync_sched_exp_online_cleanup(cpu);
+ rcutree_affinity_setting(cpu, -1);
+ return 0;
+}
+
+int rcutree_offline_cpu(unsigned int cpu)
+{
+ rcutree_affinity_setting(cpu, cpu);
+ return 0;
+}
+
+
+int rcutree_dying_cpu(unsigned int cpu)
+{
+ struct rcu_state *rsp;
+
+ for_each_rcu_flavor(rsp)
+ rcu_cleanup_dying_cpu(rsp);
+ return 0;
+}
+
+int rcutree_dead_cpu(unsigned int cpu)
+{
+ struct rcu_state *rsp;
+
+ for_each_rcu_flavor(rsp) {
+ rcu_cleanup_dead_cpu(cpu, rsp);
+ do_nocb_deferred_wakeup(per_cpu_ptr(rsp->rda, cpu));
+ }
+ return 0;
}

#ifdef CONFIG_HOTPLUG_CPU
@@ -3851,52 +3897,6 @@ void rcu_report_dead(unsigned int cpu)
}
#endif

-/*
- * Handle CPU online/offline notification events.
- */
-int rcu_cpu_notify(struct notifier_block *self,
- unsigned long action, void *hcpu)
-{
- long cpu = (long)hcpu;
- struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
- struct rcu_node *rnp = rdp->mynode;
- struct rcu_state *rsp;
-
- switch (action) {
- case CPU_UP_PREPARE:
- case CPU_UP_PREPARE_FROZEN:
- rcu_prepare_cpu(cpu);
- rcu_prepare_kthreads(cpu);
- rcu_spawn_all_nocb_kthreads(cpu);
- break;
- case CPU_ONLINE:
- case CPU_DOWN_FAILED:
- sync_sched_exp_online_cleanup(cpu);
- rcu_boost_kthread_setaffinity(rnp, -1);
- break;
- case CPU_DOWN_PREPARE:
- rcu_boost_kthread_setaffinity(rnp, cpu);
- break;
- case CPU_DYING:
- case CPU_DYING_FROZEN:
- for_each_rcu_flavor(rsp)
- rcu_cleanup_dying_cpu(rsp);
- break;
- case CPU_DEAD:
- case CPU_DEAD_FROZEN:
- case CPU_UP_CANCELED:
- case CPU_UP_CANCELED_FROZEN:
- for_each_rcu_flavor(rsp) {
- rcu_cleanup_dead_cpu(cpu, rsp);
- do_nocb_deferred_wakeup(per_cpu_ptr(rsp->rda, cpu));
- }
- break;
- default:
- break;
- }
- return NOTIFY_OK;
-}
-
static int rcu_pm_notify(struct notifier_block *self,
unsigned long action, void *hcpu)
{
@@ -4208,10 +4208,9 @@ void __init rcu_init(void)
* this is called early in boot, before either interrupts
* or the scheduler are operational.
*/
- cpu_notifier(rcu_cpu_notify, 0);
pm_notifier(rcu_pm_notify, 0);
for_each_online_cpu(cpu)
- rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
+ rcutree_prepare_cpu(cpu);
}

#include "tree_exp.h"

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