4.9-stable review patch. If anyone has any objections, please let me know.
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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;