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Subject[patch V2 56/67] timers/core: Convert to hotplug state machine
From: Richard Cochran <rcochran@linutronix.de>

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@linutronix.de>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
---
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
@@ -17,6 +17,7 @@ enum cpuhp_state {
CPUHP_WORKQUEUE_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
@@ -273,4 +273,10 @@ 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
@@ -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.
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1804,7 +1804,7 @@ static void migrate_timer_list(struct ti
}
}

-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);
}


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