Commit 26456f87 authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

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: 500462a9 ("timers: Switch to a non-cascading wheel")
Reported-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: default avatarThomas 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>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/alpine.DEB.2.20.1712272152200.2431@nanos
parent ced6d5c1

include/linux/cpuhotplug.h

+1 −1
Original line number Diff line number Diff line
@@ -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,

include/linux/timer.h

+3 −1
Original line number Diff line number Diff line
@@ -207,8 +207,10 @@ 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_prepare_cpu	NULL

#define timers_dead_cpu		NULL

#endif

kernel/cpu.c

+2 −2
Original line number Diff line number Diff line
@@ -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 */

kernel/time/timer.c

+15 −0
Original line number Diff line number Diff line
@@ -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;

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