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%3Ba=su...

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 stable@vger.kernel.org know about it.

From 26456f87aca7157c057de65c9414b37f1ab881d1 Mon Sep 17 00:00:00 2001

From: Thomas Gleixner tglx@linutronix.de Date: Wed, 27 Dec 2017 21:37:25 +0100 Subject: timers: Reinitialize per cpu bases on hotplug

From: Thomas Gleixner tglx@linutronix.de

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.

Fixes: 500462a9de65 ("timers: Switch to a non-cascading wheel") Reported-by: Paul E. McKenney paulmck@linux.vnet.ibm.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: Peter Zijlstra peterz@infradead.org Cc: Frederic Weisbecker fweisbec@gmail.com Cc: Sebastian Siewior bigeasy@linutronix.de Cc: Anna-Maria Gleixner anna-maria@linutronix.de Link: https://lkml.kernel.org/r/alpine.DEB.2.20.1712272152200.2431@nanos Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- 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(-)

--- a/include/linux/cpuhotplug.h +++ b/include/linux/cpuhotplug.h @@ -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, --- a/include/linux/timer.h +++ b/include/linux/timer.h @@ -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 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -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 */ --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -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 tglx@linutronix.de 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