linux-kernel - Re: [PATCH] tracing: Reset the function filter after completing trampoline/graph selftest

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Date:   Tue, 26 Apr 2022 16:00:35 +0800
From:   Li Huafei <lihuafei1@...wei.com>
To:     Steven Rostedt <rostedt@...dmis.org>
CC:     <jolsa@...hat.com>, <mingo@...hat.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing: Reset the function filter after completing
 trampoline/graph selftest

Hi Steve,

On 2022/4/26 6:58, Steven Rostedt wrote:
> On Mon, 18 Apr 2022 15:39:58 +0800
> Li Huafei <lihuafei1@...wei.com> wrote:
>
>> The direct trampoline and graph coexistence test sets global_ops to
>> trace only 'trace_selftest_dynamic_test_func', but does not reset it
>> after the test is completed, resulting in the function filter being set
>> already after the system starts. Although it can be reset through the
>> tracefs interface, it is more or less confusing to the user, and we
>> should reset it to trace all functions after the trampoline/graph test
>> completes.
>>
>> Fixes: 130c08065848 ("tracing: Add trampoline/graph selftest")
>> Signed-off-by: Li Huafei <lihuafei1@...wei.com>
>> ---
>>   kernel/trace/trace_selftest.c | 12 ++++++++----
>>   1 file changed, 8 insertions(+), 4 deletions(-)
>>
>> diff --git a/kernel/trace/trace_selftest.c b/kernel/trace/trace_selftest.c
>> index abcadbe933bb..e89f72571f8e 100644
>> --- a/kernel/trace/trace_selftest.c
>> +++ b/kernel/trace/trace_selftest.c
>> @@ -866,12 +866,12 @@ trace_selftest_startup_function_graph(struct tracer *trace,
>>   	ret = register_ftrace_direct((unsigned long) DYN_FTRACE_TEST_NAME,
>>   				     (unsigned long) trace_direct_tramp);
>>   	if (ret)
>> -		goto out;
>> +		goto reset_filter;
>>   
>>   	ret = register_ftrace_graph(&fgraph_ops);
>>   	if (ret) {
>>   		warn_failed_init_tracer(trace, ret);
>> -		goto out;
>> +		goto reset_filter;
>>   	}
>>   
>>   	DYN_FTRACE_TEST_NAME();
>> @@ -887,14 +887,18 @@ trace_selftest_startup_function_graph(struct tracer *trace,
>>   	ret = unregister_ftrace_direct((unsigned long) DYN_FTRACE_TEST_NAME,
>>   				       (unsigned long) trace_direct_tramp);
>>   	if (ret)
>> -		goto out;
>> +		goto reset_filter;
>>   
>>   	tracing_start();
>>   
>>   	if (!ret && !count) {
>>   		ret = -1;
>> -		goto out;
>> +		goto reset_filter;
> No need for all the 'goto reset_filter', if this function fails, then the
> tracer is disabled, and there's no reason to clear the filter. In fact, it
Thank you for the review. I see that we will disable function_graph tracer:

      /* Stop it if we failed */
      if (ret)
            ftrace_graph_stop();

But there is no function tracer disabled. Am I missing something that 
would disable the function tracer?


> may cause a crash (because something bad happened).

Yes, so should we kill ftrace when the function_graph test fails?

Thanks,
Huafei

>
> -- Steve
>
>
>>   	}
>> +
>> +reset_filter:
>> +	/* Enable tracing on all functions again */
>> +	ftrace_set_global_filter(NULL, 0, 1);
>>   #endif
>>   
>>   	/* Don't test dynamic tracing, the function tracer already did */
> .