hrtimer: Report offline hrtimer enqueue

The hrtimers migration on CPU-down hotplug process has been moved
earlier, before the CPU actually goes to die. This leaves a small window
of opportunity to queue an hrtimer in a blind spot, leaving it ignored.

For example a practical case has been reported with RCU waking up a
SCHED_FIFO task right before the CPUHP_AP_IDLE_DEAD stage, queuing that
way a sched/rt timer to the local offline CPU.

Make sure such situations never go unnoticed and warn when that happens.

Fixes: 5c0930ccaad5 ("hrtimers: Push pending hrtimers away from outgoing CPU earlier")
Reported-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20240129235646.3171983-4-boqun.feng@gmail.com

diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index 87e3bedf8eb00323c102787243e7dbfd045ba4e9..641c4567cfa7aee830f8ad0b52abb24bcbe353a8 100644 (file)
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -157,6 +157,7 @@ enum  hrtimer_base_type {
  * @max_hang_time:     Maximum time spent in hrtimer_interrupt
  * @softirq_expiry_lock: Lock which is taken while softirq based hrtimer are
  *                      expired
+ * @online:            CPU is online from an hrtimers point of view
  * @timer_waiters:     A hrtimer_cancel() invocation waits for the timer
  *                     callback to finish.
  * @expires_next:      absolute time of the next event, is required for remote
@@ -179,7 +180,8 @@ struct hrtimer_cpu_base {
        unsigned int                    hres_active             : 1,
                                        in_hrtirq               : 1,
                                        hang_detected           : 1,
-                                       softirq_activated       : 1;
+                                       softirq_activated       : 1,
+                                       online                  : 1;
 #ifdef CONFIG_HIGH_RES_TIMERS
        unsigned int                    nr_events;
        unsigned short                  nr_retries;

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 760793998cdd703a387c64a792a7b7f7dab552d5..edb0f821dceaa1720ac94fc53f4002a1e5f7bdd3 100644 (file)
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1085,6 +1085,7 @@ static int enqueue_hrtimer(struct hrtimer *timer,
                           enum hrtimer_mode mode)
 {
        debug_activate(timer, mode);
+       WARN_ON_ONCE(!base->cpu_base->online);
 
        base->cpu_base->active_bases |= 1 << base->index;
 
@@ -2183,6 +2184,7 @@ int hrtimers_prepare_cpu(unsigned int cpu)
        cpu_base->softirq_next_timer = NULL;
        cpu_base->expires_next = KTIME_MAX;
        cpu_base->softirq_expires_next = KTIME_MAX;
+       cpu_base->online = 1;
        hrtimer_cpu_base_init_expiry_lock(cpu_base);
        return 0;
 }
@@ -2250,6 +2252,7 @@ int hrtimers_cpu_dying(unsigned int dying_cpu)
        smp_call_function_single(ncpu, retrigger_next_event, NULL, 0);
 
        raw_spin_unlock(&new_base->lock);
+       old_base->online = 0;
        raw_spin_unlock(&old_base->lock);
 
        return 0;