linux-kernel - [tip:timers/urgent] timers: Reinitialize per cpu bases on hotplug

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Message-ID: <tip-26456f87aca7157c057de65c9414b37f1ab881d1@git.kernel.org>
Date:   Fri, 29 Dec 2017 14:46:13 -0800
From:   tip-bot for Thomas Gleixner <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     paulmck@...ux.vnet.ibm.com, bigeasy@...utronix.de,
        anna-maria@...utronix.de, fweisbec@...il.com, mingo@...nel.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.de,
        peterz@...radead.org, hpa@...or.com
Subject: [tip:timers/urgent] timers: Reinitialize per cpu bases on hotplug

Commit-ID:  26456f87aca7157c057de65c9414b37f1ab881d1
Gitweb:     https://git.kernel.org/tip/26456f87aca7157c057de65c9414b37f1ab881d1
Author:     Thomas Gleixner <tglx@...utronix.de>
AuthorDate: Wed, 27 Dec 2017 21:37:25 +0100
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Fri, 29 Dec 2017 23:13:09 +0100

timers: Reinitialize per cpu bases on hotplug

The timer wheel bases are not (re)initialized on CPU hotplug. That leaves
them with a potentially stale clk and next_expiry valuem, which can cause
trouble then the CPU is plugged.

Add a prepare callback which forwards the clock, sets next_expiry to far in
the future and reset the control flags to a known state.

Set base->must_forward_clk so the first timer which is queued will try to
forward the clock to current jiffies.

Fixes: 500462a9de65 ("timers: Switch to a non-cascading wheel")
Reported-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Sebastian Siewior <bigeasy@...utronix.de>
Cc: Anna-Maria Gleixner <anna-maria@...utronix.de>
Cc: stable@...r.kernel.org
Link: https://lkml.kernel.org/r/alpine.DEB.2.20.1712272152200.2431@nanos

---
 include/linux/cpuhotplug.h |  2 +-
 include/linux/timer.h      |  4 +++-
 kernel/cpu.c               |  4 ++--
 kernel/time/timer.c        | 15 +++++++++++++++
 4 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
index 201ab72..1a32e55 100644
--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -86,7 +86,7 @@ enum cpuhp_state {
 	CPUHP_MM_ZSWP_POOL_PREPARE,
 	CPUHP_KVM_PPC_BOOK3S_PREPARE,
 	CPUHP_ZCOMP_PREPARE,
-	CPUHP_TIMERS_DEAD,
+	CPUHP_TIMERS_PREPARE,
 	CPUHP_MIPS_SOC_PREPARE,
 	CPUHP_BP_PREPARE_DYN,
 	CPUHP_BP_PREPARE_DYN_END		= CPUHP_BP_PREPARE_DYN + 20,
diff --git a/include/linux/timer.h b/include/linux/timer.h
index 04af640..2448f9c 100644
--- a/include/linux/timer.h
+++ b/include/linux/timer.h
@@ -207,9 +207,11 @@ unsigned long round_jiffies_up(unsigned long j);
 unsigned long round_jiffies_up_relative(unsigned long j);
 
 #ifdef CONFIG_HOTPLUG_CPU
+int timers_prepare_cpu(unsigned int cpu);
 int timers_dead_cpu(unsigned int cpu);
 #else
-#define timers_dead_cpu NULL
+#define timers_prepare_cpu	NULL
+#define timers_dead_cpu		NULL
 #endif
 
 #endif
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 41376c3..9785847 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1277,9 +1277,9 @@ static struct cpuhp_step cpuhp_bp_states[] = {
 	 * before blk_mq_queue_reinit_notify() from notify_dead(),
 	 * otherwise a RCU stall occurs.
 	 */
-	[CPUHP_TIMERS_DEAD] = {
+	[CPUHP_TIMERS_PREPARE] = {
 		.name			= "timers:dead",
-		.startup.single		= NULL,
+		.startup.single		= timers_prepare_cpu,
 		.teardown.single	= timers_dead_cpu,
 	},
 	/* Kicks the plugged cpu into life */
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 19a9c3d..6be576e 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1853,6 +1853,21 @@ static void migrate_timer_list(struct timer_base *new_base, struct hlist_head *h
 	}
 }
 
+int timers_prepare_cpu(unsigned int cpu)
+{
+	struct timer_base *base;
+	int b;
+
+	for (b = 0; b < NR_BASES; b++) {
+		base = per_cpu_ptr(&timer_bases[b], cpu);
+		base->clk = jiffies;
+		base->next_expiry = base->clk + NEXT_TIMER_MAX_DELTA;
+		base->is_idle = false;
+		base->must_forward_clk = true;
+	}
+	return 0;
+}
+
 int timers_dead_cpu(unsigned int cpu)
 {
 	struct timer_base *old_base;