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

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Message-ID: <CAOJe8K0EKnRZLnh02m8ZPWhfxwG4khwPDda71BP5MQm0j2j=JA@mail.gmail.com>
Date:	Sun, 14 Feb 2016 23:19:42 +0300
From:	Denis Kirjanov <kda@...ux-powerpc.org>
To:	Steven Rostedt <rostedt@...dmis.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 2/14/16, Steven Rostedt <rostedt@...dmis.org> wrote:
> 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?

Can you take it as a fix for now. I'll post the follow-up patch then
for rcu and offline cpus
issue.

Thanks!

>
> -- Steve
>
>>  );
>>
>>  DEFINE_EVENT_CONDITION(kmem_free, kmem_cache_free,
>
>