linux-kernel - Re: [PATCH 1/2] tracing/mm: don't trace kfree on offline CPUs

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Date:	Sun, 14 Feb 2016 11:45:37 -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 1/2] tracing/mm: don't trace kfree on offline CPUs

On Sat, 13 Feb 2016 21:22:52 +0300
Denis Kirjanov <kda@...ux-powerpc.org> wrote:

> -DEFINE_EVENT(kmem_free, kfree,
> +DEFINE_EVENT_CONDITION(kmem_free, kfree,
>  
>  	TP_PROTO(unsigned long call_site, const void *ptr),
>  
> -	TP_ARGS(call_site, ptr)
> +	TP_ARGS(call_site, ptr),
> +
> +	/*
> +	 * This trace can be potentially called from an offlined cpu.
> +	 * Since trace points use RCU and RCU should not be used from
> +	 * offline cpus, filter such calls out.
> +	 * While this trace can be called from a preemptable section,
> +	 * it has no impact on the condition since tasks can migrate
> +	 * only from online cpus to other online cpus. Thus its safe
> +	 * to use raw_smp_processor_id.
> +	 */
> +	TP_CONDITION(cpu_online(raw_smp_processor_id()))

This is starting to become a common occurrence. Perhaps it is best to
just hardcode this into the tracepoint code itself?

-- Steve

>  );
>  
>  DEFINE_EVENT_CONDITION(kmem_free, kmem_cache_free,