On Thu, Mar 11, 2021 at 01:37:04PM +0100, Frederic Weisbecker wrote: > Enqueuing a local timer after the tick has been stopped will result in > the timer being ignored until the next random interrupt. > > Perform sanity checks to report these situations. > > Reviewed-by: Rafael J. Wysocki <[email protected]> > Signed-off-by: Frederic Weisbecker <[email protected]> > Cc: Peter Zijlstra <[email protected]> > Cc: Thomas Gleixner <[email protected]> > Cc: Ingo Molnar <[email protected]> > Cc: Paul E. McKenney <[email protected]> > --- > kernel/sched/core.c | 20 +++++++++++++++++++- > 1 file changed, 19 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index ca2bb629595f..24552911f92b 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -674,6 +674,22 @@ int get_nohz_timer_target(void) > return cpu; > } > > +/* Make sure the timer won't be ignored in dynticks-idle case */ > +static void wake_idle_assert_possible(void) > +{ > +#ifdef CONFIG_SCHED_DEBUG > + /* > + * Timers are re-evaluated after idle IRQs. In case of softirq, > + * we assume IRQ tail. Ksoftirqd shouldn't reach here as the > + * timer base wouldn't be idle. And inline softirq processing > + * after a call to local_bh_enable() within idle loop sound too > + * fun to be considered here. > + */ > + WARN_ONCE(in_task(), > + "Late timer enqueue may be ignored\n"); > +#endif > +} > + > /* > * When add_timer_on() enqueues a timer into the timer wheel of an > * idle CPU then this timer might expire before the next timer event > @@ -688,8 +704,10 @@ static void wake_up_idle_cpu(int cpu) > { > struct rq *rq = cpu_rq(cpu); > > - if (cpu == smp_processor_id()) > + if (cpu == smp_processor_id()) { > + wake_idle_assert_possible(); > return; > + } > > if (set_nr_and_not_polling(rq->idle)) > smp_send_reschedule(cpu);
I'm not entirely sure I understand this one. What's the callchain that leads to this?
