Re: WARN_ON_ONCE(in_nmi()) hit in irq_work_queue_on

Peter Zijlstra
2014-08-06T17:01:55Z

> Sigh, that's d84153d6c96f61a so that's been there a while, and been
> broken equally long.
>
> So this is where we run a low period (!freq) hardware event on a
> nohz_full cpu or so? And because it throttles, we need to kick the tick
> into action to unthrottle it.
>
> I suppose there's a good reason I never build with that nohz_full
> nonsense enabled :/
>
> Not sure how we should go fix that, you can't just issue random IPIs
> from NMI context.

OK, thinking one more second would've done it, how about so?

---
include/linux/perf_event.h | 7 ++++---
kernel/events/core.c | 8 +++++++-
2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 707617a8c0f6..177411e3ffc4 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -421,9 +421,10 @@ struct perf_event {
struct fasync_struct *fasync;

/* delayed work for NMIs and such */
- int pending_wakeup;
- int pending_kill;
- int pending_disable;
+ int pending_kill : 16;
+ int pending_wakeup : 1;
+ int pending_disable : 1;
+ int pending_nohz_kick : 1;
struct irq_work pending;

atomic_t event_limit;
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 1cf24b3e42ec..e95fca20e26f 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4258,6 +4258,11 @@ static void perf_pending_event(struct irq_work *entry)
event->pending_wakeup = 0;
perf_event_wakeup(event);
}
+
+ if (event->pending_nohz_kick) {
+ event->pending_nohz_kick = 0;
+ tick_nohz_full_kick();
+ }
}

/*
@@ -5431,7 +5436,8 @@ static int __perf_event_overflow(struct perf_event *event,
__this_cpu_inc(perf_throttled_count);
hwc->interrupts = MAX_INTERRUPTS;
perf_log_throttle(event, 0);
- tick_nohz_full_kick();
+ event->pending_nohz_kick = 1;
+ irq_work_queue(&event->pending);
ret = 1;
}
}