linux-kernel - Re: [for-next][PATCH 00/18] function_graph: Add separate depth counter to prevent trace corruption

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Date:   Wed, 28 Nov 2018 16:00:21 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Joe Lawrence <joe.lawrence@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-arch@...r.kernel.org,
        Joel Fernandes <joel@...lfernandes.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>
Subject: Re: [for-next][PATCH 00/18] function_graph: Add separate depth
 counter to prevent trace corruption

On Wed, 28 Nov 2018 15:39:31 -0500
Joe Lawrence <joe.lawrence@...hat.com> wrote:

> Hi Steve,
> 
> With your ftrace/urgent branch linked above, if I try a quick
> function_graph test like the following:
> 
>   SYSFS=/sys/kernel/debug/tracing
> 
>   echo 0 > "$SYSFS/tracing_on"
>   echo cmdline_proc_show > "$SYSFS/set_graph_function"
>   echo function_graph > "$SYSFS/current_tracer"
>   echo 1 > "$SYSFS/tracing_on"
> 
> I see a bunch of scheduler interrupt functions in the trace/trace_pipe
> without even invoking cmdline_proc_show().
> 
> This tests works as expected with Linux 4.20-rc3 though:
> 
>   % cat /sys/kernel/debug/tracing/trace_pipe
>    2)               |  cmdline_proc_show() {
>    2)   0.320 us    |    seq_puts();
>    2)   0.030 us    |    seq_putc();
>    2)   1.352 us    |  }
> 
> Operator error, or did the patchset break something?

Nope, that does seem to be a bug :-/

-- Steve