linux-kernel - [tip:smp/hotplug] timers/core: Convert to hotplug state machine

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Date:	Tue, 19 Jul 2016 00:27:29 -0700
From:	tip-bot for Richard Cochran <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	john.stultz@...aro.org, torvalds@...ux-foundation.org,
	linux-kernel@...r.kernel.org, hpa@...or.com,
	anna-maria@...utronix.de, bigeasy@...utronix.de,
	peterz@...radead.org, tglx@...utronix.de, oleg@...hat.com,
	linux@...musvillemoes.dk, mingo@...nel.org, rcochran@...utronix.de
Subject: [tip:smp/hotplug] timers/core: Convert to hotplug state machine

Commit-ID:  24f73b99716a9cd8cbb345c41ced6b3b5ed94006
Gitweb:     http://git.kernel.org/tip/24f73b99716a9cd8cbb345c41ced6b3b5ed94006
Author:     Richard Cochran <rcochran@...utronix.de>
AuthorDate: Wed, 13 Jul 2016 17:16:59 +0000
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 15 Jul 2016 10:41:42 +0200

timers/core: Convert to hotplug state machine

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@...utronix.de>
Signed-off-by: Anna-Maria Gleixner <anna-maria@...utronix.de>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: John Stultz <john.stultz@...aro.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Rasmus Villemoes <linux@...musvillemoes.dk>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: rt@...utronix.de
Link: http://lkml.kernel.org/r/20160713153337.566790058@linutronix.de
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 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(-)

diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
index 04ecc55..15d46d2 100644
--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -16,6 +16,7 @@ enum cpuhp_state {
 	CPUHP_X86_APB_DEAD,
 	CPUHP_WORKQUEUE_PREP,
 	CPUHP_HRTIMERS_PREPARE,
+	CPUHP_TIMERS_DEAD,
 	CPUHP_NOTIFY_PREPARE,
 	CPUHP_BRINGUP_CPU,
 	CPUHP_AP_IDLE_DEAD,
diff --git a/include/linux/timer.h b/include/linux/timer.h
index 4419506..51d601f 100644
--- a/include/linux/timer.h
+++ b/include/linux/timer.h
@@ -273,4 +273,10 @@ unsigned long __round_jiffies_up_relative(unsigned long j, int cpu);
 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
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 85500e7..e1017d9 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1195,6 +1195,11 @@ 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.
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index cb9ab40..555670a 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1804,7 +1804,7 @@ static void migrate_timer_list(struct timer_base *new_base, struct hlist_head *h
 	}
 }
 
-static void migrate_timers(int cpu)
+int timers_dead_cpu(unsigned int cpu)
 {
 	struct timer_base *old_base;
 	struct timer_base *new_base;
@@ -1831,29 +1831,9 @@ static void migrate_timers(int cpu)
 		spin_unlock_irq(&new_base->lock);
 		put_cpu_ptr(&timer_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)
@@ -1881,7 +1861,6 @@ void __init init_timers(void)
 {
 	init_timer_cpus();
 	init_timer_stats();
-	timer_register_cpu_notifier();
 	open_softirq(TIMER_SOFTIRQ, run_timer_softirq);
 }