@@ -34,6 +34,21 @@ config ARCH_HAS_SUBPAGE_FAULTS
config HOTPLUG_SMT
bool
+# Selected by HOTPLUG_CORE_SYNC_DEAD or HOTPLUG_CORE_SYNC_FULL
+config HOTPLUG_CORE_SYNC
+ bool
+
+# Basic CPU dead synchronization selected by architecture
+config HOTPLUG_CORE_SYNC_DEAD
+ bool
+ select HOTPLUG_CORE_SYNC
+
+# Full CPU synchronization with alive state selected by architecture
+config HOTPLUG_CORE_SYNC_FULL
+ bool
+ select HOTPLUG_CORE_SYNC_DEAD if HOTPLUG_CPU
+ select HOTPLUG_CORE_SYNC
+
config GENERIC_ENTRY
bool
@@ -517,4 +517,16 @@ void cpuhp_online_idle(enum cpuhp_state
static inline void cpuhp_online_idle(enum cpuhp_state state) { }
#endif
+void cpuhp_ap_sync_alive(void);
+void arch_cpuhp_sync_state_poll(void);
+void arch_cpuhp_cleanup_kick_cpu(unsigned int cpu);
+
+#ifdef CONFIG_HOTPLUG_CORE_SYNC_DEAD
+void cpuhp_ap_report_dead(void);
+void arch_cpuhp_cleanup_dead_cpu(unsigned int cpu);
+#else
+static inline void cpuhp_ap_report_dead(void) { }
+static inline void arch_cpuhp_cleanup_dead_cpu(unsigned int cpu) { }
+#endif
+
#endif
@@ -17,6 +17,7 @@
#include <linux/cpu.h>
#include <linux/oom.h>
#include <linux/rcupdate.h>
+#include <linux/delay.h>
#include <linux/export.h>
#include <linux/bug.h>
#include <linux/kthread.h>
@@ -59,6 +60,7 @@
* @last: For multi-instance rollback, remember how far we got
* @cb_state: The state for a single callback (install/uninstall)
* @result: Result of the operation
+ * @ap_sync_state: State for AP synchronization
* @done_up: Signal completion to the issuer of the task for cpu-up
* @done_down: Signal completion to the issuer of the task for cpu-down
*/
@@ -76,6 +78,7 @@ struct cpuhp_cpu_state {
struct hlist_node *last;
enum cpuhp_state cb_state;
int result;
+ atomic_t ap_sync_state;
struct completion done_up;
struct completion done_down;
#endif
@@ -276,6 +279,182 @@ static bool cpuhp_is_atomic_state(enum c
return CPUHP_AP_IDLE_DEAD <= state && state < CPUHP_AP_ONLINE;
}
+/* Synchronization state management */
+enum cpuhp_sync_state {
+ SYNC_STATE_DEAD,
+ SYNC_STATE_KICKED,
+ SYNC_STATE_SHOULD_DIE,
+ SYNC_STATE_ALIVE,
+ SYNC_STATE_SHOULD_ONLINE,
+ SYNC_STATE_ONLINE,
+};
+
+#ifdef CONFIG_HOTPLUG_CORE_SYNC
+/**
+ * cpuhp_ap_update_sync_state - Update synchronization state during bringup/teardown
+ * @state: The synchronization state to set
+ *
+ * No synchronization point. Just update of the synchronization state, but implies
+ * a full barrier so that the AP changes are visible before the control CPU proceeds.
+ */
+static inline void cpuhp_ap_update_sync_state(enum cpuhp_sync_state state)
+{
+ atomic_t *st = this_cpu_ptr(&cpuhp_state.ap_sync_state);
+
+ (void)atomic_xchg(st, state);
+}
+
+void __weak arch_cpuhp_sync_state_poll(void) { cpu_relax(); }
+
+static bool cpuhp_wait_for_sync_state(unsigned int cpu, enum cpuhp_sync_state state,
+ enum cpuhp_sync_state next_state)
+{
+ atomic_t *st = per_cpu_ptr(&cpuhp_state.ap_sync_state, cpu);
+ ktime_t now, end, start = ktime_get();
+ int sync;
+
+ end = start + 10ULL * NSEC_PER_SEC;
+
+ sync = atomic_read(st);
+ while (1) {
+ if (sync == state) {
+ if (!atomic_try_cmpxchg(st, &sync, next_state))
+ continue;
+ return true;
+ }
+
+ now = ktime_get();
+ if (now > end) {
+ /* Timeout. Leave the state unchanged */
+ return false;
+ } else if (now - start < NSEC_PER_MSEC) {
+ /* Poll for one millisecond */
+ arch_cpuhp_sync_state_poll();
+ } else {
+ usleep_range_state(USEC_PER_MSEC, 2 * USEC_PER_MSEC, TASK_UNINTERRUPTIBLE);
+ }
+ sync = atomic_read(st);
+ }
+ return true;
+}
+#else /* CONFIG_HOTPLUG_CORE_SYNC */
+static inline void cpuhp_ap_update_sync_state(enum cpuhp_sync_state state) { }
+#endif /* !CONFIG_HOTPLUG_CORE_SYNC */
+
+#ifdef CONFIG_HOTPLUG_CORE_SYNC_DEAD
+/**
+ * cpuhp_ap_report_dead - Update synchronization state to DEAD
+ *
+ * No synchronization point. Just update of the synchronization state.
+ */
+void cpuhp_ap_report_dead(void)
+{
+ cpuhp_ap_update_sync_state(SYNC_STATE_DEAD);
+}
+
+void __weak arch_cpuhp_cleanup_dead_cpu(unsigned int cpu) { }
+
+/*
+ * Late CPU shutdown synchronization point. Cannot use cpuhp_state::done_down
+ * because the AP cannot issue complete() at this stage.
+ */
+static void cpuhp_bp_sync_dead(unsigned int cpu)
+{
+ atomic_t *st = per_cpu_ptr(&cpuhp_state.ap_sync_state, cpu);
+ int sync = atomic_read(st);
+
+ do {
+ /* CPU can have reported dead already. Don't overwrite that! */
+ if (sync == SYNC_STATE_DEAD)
+ break;
+ } while (!atomic_try_cmpxchg(st, &sync, SYNC_STATE_SHOULD_DIE));
+
+ if (cpuhp_wait_for_sync_state(cpu, SYNC_STATE_DEAD, SYNC_STATE_DEAD)) {
+ /* CPU reached dead state. Invoke the cleanup function */
+ arch_cpuhp_cleanup_dead_cpu(cpu);
+ return;
+ }
+
+ /* No further action possible. Emit message and give up. */
+ pr_err("CPU%u failed to report dead state\n", cpu);
+}
+#else /* CONFIG_HOTPLUG_CORE_SYNC_DEAD */
+static inline void cpuhp_bp_sync_dead(unsigned int cpu) { }
+#endif /* !CONFIG_HOTPLUG_CORE_SYNC_DEAD */
+
+#ifdef CONFIG_HOTPLUG_CORE_SYNC_FULL
+/**
+ * cpuhp_ap_sync_alive - Synchronize AP with the control CPU once it is alive
+ *
+ * Updates the AP synchronization state to SYNC_STATE_ALIVE and waits
+ * for the BP to release it.
+ */
+void cpuhp_ap_sync_alive(void)
+{
+ atomic_t *st = this_cpu_ptr(&cpuhp_state.ap_sync_state);
+
+ cpuhp_ap_update_sync_state(SYNC_STATE_ALIVE);
+
+ /* Wait for the control CPU to release it. */
+ while (atomic_read(st) != SYNC_STATE_SHOULD_ONLINE)
+ cpu_relax();
+}
+
+static bool cpuhp_can_boot_ap(unsigned int cpu)
+{
+ atomic_t *st = per_cpu_ptr(&cpuhp_state.ap_sync_state, cpu);
+ int sync = atomic_read(st);
+
+again:
+ switch (sync) {
+ case SYNC_STATE_DEAD:
+ /* CPU is properly dead */
+ break;
+ case SYNC_STATE_KICKED:
+ /* CPU did not come up in previous attempt */
+ break;
+ case SYNC_STATE_ALIVE:
+ /* CPU is stuck cpuhp_ap_sync_alive(). */
+ break;
+ default:
+ /* CPU failed to report online or dead and is in limbo state. */
+ return false;
+ }
+
+ /* Prepare for booting */
+ if (!atomic_try_cmpxchg(st, &sync, SYNC_STATE_KICKED))
+ goto again;
+
+ return true;
+}
+
+void __weak arch_cpuhp_cleanup_kick_cpu(unsigned int cpu) { }
+
+/*
+ * Early CPU bringup synchronization point. Cannot use cpuhp_state::done_up
+ * because the AP cannot issue complete() so early in the bringup.
+ */
+static int cpuhp_bp_sync_alive(unsigned int cpu)
+{
+ int ret = 0;
+
+ if (!IS_ENABLED(CONFIG_HOTPLUG_CORE_SYNC_FULL))
+ return 0;
+
+ if (!cpuhp_wait_for_sync_state(cpu, SYNC_STATE_ALIVE, SYNC_STATE_SHOULD_ONLINE)) {
+ pr_err("CPU%u failed to report alive state\n", cpu);
+ ret = -EIO;
+ }
+
+ /* Let the architecture cleanup the kick alive mechanics. */
+ arch_cpuhp_cleanup_kick_cpu(cpu);
+ return ret;
+}
+#else /* CONFIG_HOTPLUG_CORE_SYNC_FULL */
+static inline int cpuhp_bp_sync_alive(unsigned int cpu) { return 0; }
+static inline bool cpuhp_can_boot_ap(unsigned int cpu) { return true; }
+#endif /* !CONFIG_HOTPLUG_CORE_SYNC_FULL */
+
/* Serializes the updates to cpu_online_mask, cpu_present_mask */
static DEFINE_MUTEX(cpu_add_remove_lock);
bool cpuhp_tasks_frozen;
@@ -588,6 +767,9 @@ static int bringup_cpu(unsigned int cpu)
struct task_struct *idle = idle_thread_get(cpu);
int ret;
+ if (!cpuhp_can_boot_ap(cpu))
+ return -EAGAIN;
+
/*
* Reset stale stack state from the last time this CPU was online.
*/
@@ -610,6 +792,10 @@ static int bringup_cpu(unsigned int cpu)
if (ret)
goto out_unlock;
+ ret = cpuhp_bp_sync_alive(cpu);
+ if (ret)
+ goto out_unlock;
+
ret = bringup_wait_for_ap_online(cpu);
if (ret)
goto out_unlock;
@@ -1113,6 +1299,8 @@ static int takedown_cpu(unsigned int cpu
/* This actually kills the CPU. */
__cpu_die(cpu);
+ cpuhp_bp_sync_dead(cpu);
+
tick_cleanup_dead_cpu(cpu);
rcutree_migrate_callbacks(cpu);
return 0;
@@ -1359,8 +1547,10 @@ void cpuhp_online_idle(enum cpuhp_state
if (state != CPUHP_AP_ONLINE_IDLE)
return;
+ cpuhp_ap_update_sync_state(SYNC_STATE_ONLINE);
+
/*
- * Unpart the stopper thread before we start the idle loop (and start
+ * Unpark the stopper thread before we start the idle loop (and start
* scheduling); this ensures the stopper task is always available.
*/
stop_machine_unpark(smp_processor_id());
@@ -2737,6 +2927,7 @@ void __init boot_cpu_hotplug_init(void)
{
#ifdef CONFIG_SMP
cpumask_set_cpu(smp_processor_id(), &cpus_booted_once_mask);
+ atomic_set(this_cpu_ptr(&cpuhp_state.ap_sync_state), SYNC_STATE_ONLINE);
#endif
this_cpu_write(cpuhp_state.state, CPUHP_ONLINE);
this_cpu_write(cpuhp_state.target, CPUHP_ONLINE);
@@ -326,6 +326,7 @@ void smpboot_unregister_percpu_thread(st
}
EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);
+#ifndef CONFIG_HOTPLUG_CORE_SYNC
static DEFINE_PER_CPU(atomic_t, cpu_hotplug_state) = ATOMIC_INIT(CPU_POST_DEAD);
/*
@@ -488,3 +489,4 @@ bool cpu_report_death(void)
}
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
+#endif /* !CONFIG_HOTPLUG_CORE_SYNC */