Merge tag 'timers_urgent_for_v5.16_rc4' of git://git.kernel.org/pub/scm/linux/kernel...

Pull timer fix from Borislav Petkov:

 - Prevent a tick storm when a dedicated timekeeper CPU in nohz_full
   mode runs for prolonged periods with interrupts disabled and ends up
   programming the next tick in the past, leading to that storm

* tag 'timers_urgent_for_v5.16_rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  timers/nohz: Last resort update jiffies on nohz_full IRQ entry

diff --git a/kernel/softirq.c b/kernel/softirq.c
index 322b65d..41f4709 100644 (file)
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -595,7 +595,8 @@ void irq_enter_rcu(void)
 {
        __irq_enter_raw();
 
-       if (is_idle_task(current) && (irq_count() == HARDIRQ_OFFSET))
+       if (tick_nohz_full_cpu(smp_processor_id()) ||
+           (is_idle_task(current) && (irq_count() == HARDIRQ_OFFSET)))
                tick_irq_enter();
 
        account_hardirq_enter(current);

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 6bffe5a..17a283c 100644 (file)
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -1375,6 +1375,13 @@ static inline void tick_nohz_irq_enter(void)
        now = ktime_get();
        if (ts->idle_active)
                tick_nohz_stop_idle(ts, now);
+       /*
+        * If all CPUs are idle. We may need to update a stale jiffies value.
+        * Note nohz_full is a special case: a timekeeper is guaranteed to stay
+        * alive but it might be busy looping with interrupts disabled in some
+        * rare case (typically stop machine). So we must make sure we have a
+        * last resort.
+        */
        if (ts->tick_stopped)
                tick_nohz_update_jiffies(now);
 }