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

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Date:   Wed, 27 Apr 2022 09:39:27 +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


On 2022/4/26 23:31, Steven Rostedt wrote:
> On Tue, 26 Apr 2022 16:00:35 +0800
> Li Huafei <lihuafei1@...wei.com> wrote:
>
>>> 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?
> No, but if we are triggering these, then something really bad has happened,
> and function tracer is possibly corrupted too, or should not be trusted.
>
>>
>>> may cause a crash (because something bad happened).
>> Yes, so should we kill ftrace when the function_graph test fails?
> No, but the system should be fixed. These should never trigger on any
> production system, because it means something really bad is happening and
> we do not know what.
>
> Not resetting the filters may even be useful in debugging it. So that's
> another reason to not do so.


That makes sense.  I will remove all "goto reset_filter" from the error 
path and only reset the filter when the test passes.


Thanks,

Huafei


>
> -- Steve
> .