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 15:39:31 -0500
From:   Joe Lawrence <joe.lawrence@...hat.com>
To:     Steven Rostedt <rostedt@...dmis.org>
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, Nov 21, 2018 at 07:28:01PM -0500, Steven Rostedt wrote:
>
> [ ... snip ... ]
>
> Feel free to test this! I'll be pushing this to linux-next and let it
> sit there a week or so before pushing it to Linus.
>
>   git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
> ftrace/urgent

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?

Regards,

-- Joe