[patch 61/66] timers: Convert to hotplug state machine

[Anna-Maria Gleixner]

From: Richard Cochran <rcochran@xxxxxxxxxxxxx>

When tearing down, call timers_dead_cpu before notify_dead.
There is a hidden dependency between:

- timers
- Block multiqueue
- rcutree

If timers_dead_cpu() comes later than blk_mq_queue_reinit_notify()
that latter function causes a RCU stall.

Signed-off-by: Richard Cochran <rcochran@xxxxxxxxxxxxx>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Signed-off-by: Anna-Maria Gleixner <anna-maria@xxxxxxxxxxxxx>

---
 include/linux/cpuhotplug.h |    1 +
 include/linux/timer.h      |    6 ++++++
 kernel/cpu.c               |    5 +++++
 kernel/time/timer.c        |   25 ++-----------------------
 4 files changed, 14 insertions(+), 23 deletions(-)

--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -18,6 +18,7 @@ enum cpuhp_state {
 	CPUHP_RCUTREE_PREP,
 	CPUHP_POWER_NUMA_PREPARE,
 	CPUHP_HRTIMERS_PREPARE,
+	CPUHP_TIMERS_DEAD,
 	CPUHP_NOTIFY_PREPARE,
 	CPUHP_BRINGUP_CPU,
 	CPUHP_AP_IDLE_DEAD,
--- a/include/linux/timer.h
+++ b/include/linux/timer.h
@@ -259,4 +259,10 @@ unsigned long __round_jiffies_up_relativ
 unsigned long round_jiffies_up(unsigned long j);
 unsigned long round_jiffies_up_relative(unsigned long j);
 
+#ifdef CONFIG_HOTPLUG_CPU
+int timers_dead_cpu(unsigned int cpu);
+#else
+#define timers_dead_cpu NULL
+#endif
+
 #endif
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1194,6 +1194,11 @@ static struct cpuhp_step cpuhp_bp_states
 		.startup = hrtimers_prepare_cpu,
 		.teardown = hrtimers_dead_cpu,
 	},
+	[CPUHP_TIMERS_DEAD] = {
+		.name = "timers dead",
+		.startup = NULL,
+		.teardown = timers_dead_cpu,
+	},
 	/*
 	 * Preparatory and dead notifiers. Will be replaced once the notifiers
 	 * are converted to states.
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1577,7 +1577,7 @@ static void migrate_timer_list(struct tv
 	}
 }
 
-static void migrate_timers(int cpu)
+int timers_dead_cpu(unsigned int cpu)
 {
 	struct tvec_base *old_base;
 	struct tvec_base *new_base;
@@ -1610,29 +1610,9 @@ static void migrate_timers(int cpu)
 	spin_unlock(&old_base->lock);
 	spin_unlock_irq(&new_base->lock);
 	put_cpu_ptr(&tvec_bases);
+	return 0;
 }
 
-static int timer_cpu_notify(struct notifier_block *self,
-				unsigned long action, void *hcpu)
-{
-	switch (action) {
-	case CPU_DEAD:
-	case CPU_DEAD_FROZEN:
-		migrate_timers((long)hcpu);
-		break;
-	default:
-		break;
-	}
-
-	return NOTIFY_OK;
-}
-
-static inline void timer_register_cpu_notifier(void)
-{
-	cpu_notifier(timer_cpu_notify, 0);
-}
-#else
-static inline void timer_register_cpu_notifier(void) { }
 #endif /* CONFIG_HOTPLUG_CPU */
 
 static void __init init_timer_cpu(int cpu)
@@ -1658,7 +1638,6 @@ void __init init_timers(void)
 {
 	init_timer_cpus();
 	init_timer_stats();
-	timer_register_cpu_notifier();
 	open_softirq(TIMER_SOFTIRQ, run_timer_softirq);
 }