On Wed, Mar 03, 2021 at 11:49:45AM -0800, Paul E. McKenney wrote: > Hello, Frederic! > > I don't see the following commit in mainline, but figured I should > check with you guys to see if the problem got solved in some other way. > Unless I hear otherwise, I will continue to carry this patch in -rcu > and will send it along for the v5.13 merge window.
I have it included in a nohz series I'm about to post but since RCU is the motivation behind doing this, it's fine if you carry it. I've just modified it a bit after a review from Peter: --- >From 7876725b8631147967bb9e65158ef1cb2bb94372 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker <frede...@kernel.org> Date: Fri, 8 Jan 2021 13:50:12 +0100 Subject: [PATCH] timer: Report ignored local enqueue in nohz mode 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. Signed-off-by: Frederic Weisbecker <frede...@kernel.org> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Thomas Gleixner <t...@linutronix.de> Cc: Ingo Molnar<mi...@kernel.org> Cc: Paul E. McKenney <paul...@kernel.org> Cc: Rafael J. Wysocki <rafael.j.wyso...@intel.com> --- 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); -- 2.25.1