hrtimer: Report offline hrtimer enqueue

commit dad6a09f3148257ac1773cd90934d721d68ab595 upstream.

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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index 3bdaa92a2cab300f15b10997912d794f1749b53d..88496ba45c480ee128e44fcf08f405ecbc5ebd73 100644 (file)
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -182,6 +182,7 @@ enum  hrtimer_base_type {
  * @hang_detected:     The last hrtimer interrupt detected a hang
  * @softirq_activated: displays, if the softirq is raised - update of softirq
  *                     related settings is not required then.
+ * @online:            CPU is online from an hrtimers point of view
  * @nr_events:         Total number of hrtimer interrupt events
  * @nr_retries:                Total number of hrtimer interrupt retries
  * @nr_hangs:          Total number of hrtimer interrupt hangs
@@ -206,7 +207,8 @@ 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 bf74f43e42af0490154d49a9bc51aa0543f5ded1..0eb5b6cc6d93903e0586b84c4ef33fb6fa7e7eef 100644 (file)
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -970,6 +970,7 @@ 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;
 
@@ -1887,6 +1888,7 @@ 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;
        return 0;
 }
 
@@ -1953,6 +1955,7 @@ 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;