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

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Date:	Fri, 5 Dec 2008 00:03:20 +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

2008/12/4 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...

>>               /*
>>                * Run a selftest on this tracer.
>>                * Here we reset the trace buffer, and set the current
>> @@ -603,6 +613,7 @@ int register_tracer(struct tracer *type)
>>               /* the test is responsible for initializing and enabling */
>>               pr_info("Testing tracer %s: ", type->name);
>>               ret = type->selftest(type, tr);
>> +             atomic_set(&tracing_selftest_running, 0);
>>               /* the test is responsible for resetting too */
>>               current_trace = saved_tracer;
>>               if (ret) {
>> @@ -3594,7 +3605,7 @@ int trace_vprintk(unsigned long ip, int depth, const char *fmt, va_list args)
>>       unsigned long flags, irq_flags;
>>       int cpu, len = 0, size, pc;
>>
>> -     if (tracing_disabled)
>> +     if (tracing_disabled || atomic_read(&tracing_selftest_running))
>>               return 0;
>>
>>       pc = preempt_count();
>> --
>
> -- Steve
>
>
--
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