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@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>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/alpine.DEB.2.20.1712272152200.2431@nanos

diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
index 201ab72..1a32e55 100644 (file)
--- 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 (file)
--- 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 (file)
--- 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 (file)
--- 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;