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

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Message-ID: <20220426113114.2005b94f@gandalf.local.home>
Date:   Tue, 26 Apr 2022 11:31:14 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Li Huafei <lihuafei1@...wei.com>
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 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.

-- Steve