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SubjectRe: [PATCH] tracing/perf: Move rcu_irq_enter/exit_irqson() to perf trace point hook
On Mon, Feb 10, 2020 at 05:06:43PM -0500, Steven Rostedt wrote:
> diff --git a/include/trace/perf.h b/include/trace/perf.h
> index dbc6c74defc3..1c94ce0cd4e2 100644
> --- a/include/trace/perf.h
> +++ b/include/trace/perf.h
> @@ -39,17 +39,27 @@ perf_trace_##call(void *__data, proto) \
> u64 __count = 1; \
> struct task_struct *__task = NULL; \
> struct hlist_head *head; \
> + bool rcu_watching; \
> int __entry_size; \
> int __data_size; \
> int rctx; \
> \
> + rcu_watching = rcu_is_watching(); \
> + \
> __data_size = trace_event_get_offsets_##call(&__data_offsets, args); \
> \
> + if (!rcu_watching) { \
> + /* Can not use RCU if rcu is not watching and in NMI */ \
> + if (in_nmi()) \
> + return; \
> + rcu_irq_enter_irqson(); \
> + } \
> + \
> head = this_cpu_ptr(event_call->perf_events); \
> if (!bpf_prog_array_valid(event_call) && \
> __builtin_constant_p(!__task) && !__task && \
> hlist_empty(head)) \
> - return; \
> + goto out; \
> \
> __entry_size = ALIGN(__data_size + sizeof(*entry) + sizeof(u32),\
> sizeof(u64)); \
> @@ -57,7 +67,7 @@ perf_trace_##call(void *__data, proto) \
> \
> entry = perf_trace_buf_alloc(__entry_size, &__regs, &rctx); \
> if (!entry) \
> - return; \
> + goto out; \
> \
> perf_fetch_caller_regs(__regs); \
> \
> @@ -68,6 +78,9 @@ perf_trace_##call(void *__data, proto) \
> perf_trace_run_bpf_submit(entry, __entry_size, rctx, \
> event_call, __count, __regs, \
> head, __task); \
> +out: \
> + if (!rcu_watching) \
> + rcu_irq_exit_irqson(); \
> }

It is probably okay to move that into perf_tp_event(), then this:

> /*
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 1694a6b57ad8..3e6f07b62515 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -719,6 +719,7 @@ void rcu_irq_exit_irqson(void)
> rcu_irq_exit();
> local_irq_restore(flags);
> }
> +EXPORT_SYMBOL_GPL(rcu_irq_exit_irqson);
>
> /*
> * Exit an RCU extended quiescent state, which can be either the
> @@ -890,6 +891,7 @@ void rcu_irq_enter_irqson(void)
> rcu_irq_enter();
> local_irq_restore(flags);
> }
> +EXPORT_SYMBOL_GPL(rcu_irq_enter_irqson);
>
> /*
> * If any sort of urgency was applied to the current CPU (for example,

can go too. Those things really should not be exported.

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