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SubjectRe: [PATCH v2] tracing/perf: Move rcu_irq_enter/exit_irqson() to perf trace point hook
On Tue, Feb 11, 2020 at 09:50:47AM -0500, Steven Rostedt wrote:
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 455451d24b4a..0abbf5e2ee62 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -8941,6 +8941,7 @@ void perf_tp_event(u16 event_type, u64 count, void *record, int entry_size,
> {
> struct perf_sample_data data;
> struct perf_event *event;
> + bool rcu_watching = rcu_is_watching();
>
> struct perf_raw_record raw = {
> .frag = {
> @@ -8949,6 +8950,17 @@ void perf_tp_event(u16 event_type, u64 count, void *record, int entry_size,
> },
> };
>
> + if (!rcu_watching) {
> + /*
> + * If nmi_enter() is traced, it is possible that
> + * RCU may not be watching "yet", and this is called.
> + * We can not call rcu_irq_enter_irqson() in this case.
> + */
> + if (unlikely(in_nmi()))
> + goto out;

unless I'm mistaken, we can simply do rcu_nmi_enter() in this case, and
rcu_nmi_exit() on the other end.

> + rcu_irq_enter_irqson();
> + }
> +
> perf_sample_data_init(&data, 0, 0);
> data.raw = &raw;
>
> @@ -8985,8 +8997,11 @@ void perf_tp_event(u16 event_type, u64 count, void *record, int entry_size,
> unlock:
> rcu_read_unlock();
> }
> -
> + if (!rcu_watching)
> + rcu_irq_exit_irqson();
> +out:
> perf_swevent_put_recursion_context(rctx);
> +
> }

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