Patch "timers: Reinitialize per cpu bases on hotplug" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

timers: Reinitialize per cpu bases on hotplug

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
timers-reinitialize-per-cpu-bases-on-hotplug.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Thomas Gleixner <[email protected]>
Date: Wed, 27 Dec 2017 21:37:25 +0100
Subject: timers: Reinitialize per cpu bases on hotplug

From: Thomas Gleixner <[email protected]>

commit 26456f87aca7157c057de65c9414b37f1ab881d1 upstream.

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.

---
 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(-)

@@ -48,7 +48,7 @@ enum cpuhp_state {
 	CPUHP_ARM_SHMOBILE_SCU_PREPARE,
 	CPUHP_SH_SH3X_PREPARE,
 	CPUHP_BLK_MQ_PREPARE,
-	CPUHP_TIMERS_DEAD,
+	CPUHP_TIMERS_PREPARE,
 	CPUHP_NOTF_ERR_INJ_PREPARE,
 	CPUHP_MIPS_SOC_PREPARE,
 	CPUHP_BRINGUP_CPU,

@@ -274,9 +274,11 @@ unsigned long round_jiffies_up(unsigned
 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

@@ -1309,9 +1309,9 @@ 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 */

@@ -1851,6 +1851,21 @@ static void migrate_timer_list(struct ti
 	}
 }
 
+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;

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/nohz-prevent-a-timer-interrupt-storm-in-tick_nohz_stop_sched_tick.patch queue-4.9/timers-invoke-timer_start_debug-where-it-makes-sense.patch queue-4.9/x86-vm86-32-switch-to-flush_tlb_mm_range-in-mark_screen_rdonly.patch queue-4.9/x86-mm-add-the-nopcid-boot-option-to-turn-off-pcid.patch queue-4.9/x86-mm-enable-cr4.pcide-on-supported-systems.patch queue-4.9/sync-objtool-s-copy-of-x86-opcode-map.txt.patch queue-4.9/x86-smpboot-remove-stale-tlb-flush-invocations.patch queue-4.9/timers-use-deferrable-base-independent-of-base-nohz_active.patch queue-4.9/x86-mm-remove-the-up-asm-tlbflush.h-code-always-use-the-formerly-smp-code.patch queue-4.9/x86-mm-reimplement-flush_tlb_page-using-flush_tlb_mm_range.patch queue-4.9/x86-mm-make-flush_tlb_mm_range-more-predictable.patch queue-4.9/x86-mm-remove-flush_tlb-and-flush_tlb_current_task.patch queue-4.9/x86-mm-disable-pcid-on-32-bit-kernels.patch queue-4.9/timers-reinitialize-per-cpu-bases-on-hotplug.patch queue-4.9/x86-mm-64-fix-reboot-interaction-with-cr4.pcide.patch