linux-kernel - Re: [PATCH 1/3] tracing/ftrace: don't insert TRACE

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Date:	Fri, 5 Dec 2008 00:04:42 +0100
From:	"Frédéric Weisbecker" <fweisbec@...il.com>
To:	"Steven Rostedt" <rostedt@...dmis.org>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"Linux Kernel" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] tracing/ftrace: don't insert TRACE_PRINT during selftests

2008/12/5 Frédéric Weisbecker <fweisbec@...il.com>:
> 2008/12/4 Steven Rostedt <rostedt@...dmis.org>:
>> The comment style should be:
>>
>> /*
>>  * comment
>>  * comment
>>  * comment
>>  */
>
> Sorry, will fix it.
>
>>
>>> +static atomic_t tracing_selftest_running = ATOMIC_INIT(0);
>>
>> Do we need that is atomic? Also, it needs to be __read_mostly.
>
>
> I thought it should be atomic to be sure the value is synchronized
> on smp when read. But actually that should have been more likely an
> int with smp_wb after writing it.
>
>>> +
>>>  /* For tracers that don't implement custom flags */
>>>  static struct tracer_opt dummy_tracer_opt[] = {
>>>       { }
>>> @@ -589,6 +597,8 @@ int register_tracer(struct tracer *type)
>>>               struct tracer *saved_tracer = current_trace;
>>>               struct trace_array *tr = &global_trace;
>>>               int i;
>>> +
>>> +             atomic_set(&tracing_selftest_running, 1);
>>
>> Enable this in the mutex lock, and we could make it a normal int.
>>
>
>
> But ftrace_printk can be called from interrupt context. I think we can loose
> some TRACE_PRINT entries at the selftests time since the tracer are not enabled
> by the user at this time, except the boot tracer...
>

But with the boot tracer enabled, there is no selftest actually :-)
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