linux-kernel - Re: [PATCH 2/2] tracing/rcu: don't trace rcu

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Date:	Sun, 14 Feb 2016 11:43:50 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Denis Kirjanov <kda@...ux-powerpc.org>
Cc:	linux-kernel@...r.kernel.org, paulmck@...ux.vnet.ibm.com
Subject: Re: [PATCH 2/2] tracing/rcu: don't trace rcu_callback on offline
 CPUs

On Sat, 13 Feb 2016 21:22:53 +0300
Denis Kirjanov <kda@...ux-powerpc.org> wrote:

> 
> diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
> index ef72c4a..5470f2f 100644
> --- a/include/trace/events/rcu.h
> +++ b/include/trace/events/rcu.h
> @@ -435,6 +435,8 @@ TRACE_EVENT(rcu_callback,
>  
>  	TP_ARGS(rcuname, rhp, qlen_lazy, qlen),
>  
> +	TP_CONDITION(cpu_online(raw_smp_processor_id())),
> +

Besides the fact that this isn't a TRACE_EVENT_CONDITION, Isn't calling
rcu_callback() dangerous from an offline CPU?

Or is calling a callback from an offline CPU OK?

Perhaps it is OK, as it doesn't need to worry about its current CPU,
just the other CPUs.

Paul?

-- Steve


>  	TP_STRUCT__entry(
>  		__field(const char *, rcuname)
>  		__field(void *, rhp)