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- Prevent a tick storm when a dedicated timekeeper CPU in nohz_full

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mode runs for prolonged periods with interrupts disabled and ends up
 programming the next tick in the past, leading to that storm
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Merge tag 'timers_urgent_for_v5.16_rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

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
This commit is contained in:
Linus Torvalds 2021-12-05 08:58:52 -08:00
commit 7587a4a5a4
2 changed files with 9 additions and 1 deletions
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3
kernel/softirq.c
View File

@ -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);

7
kernel/time/tick-sched.c
View File

@ -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);
}