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hrtimer: Report offline hrtimer enqueue

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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: 5c0930ccaa ("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
This commit is contained in:
Frederic Weisbecker 2024-01-29 15:56:36 -08:00 committed by Thomas Gleixner
parent 54be6c6c5a
commit dad6a09f31
2 changed files with 6 additions and 1 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

4
include/linux/hrtimer.h
View file

@ -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;

3
kernel/time/hrtimer.c
View file

@ -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;