Re: [for-next][PATCH 18/31] tracing: kdb: Use tracer_tracing_on/off() instead of setting per CPU disabled

[Doug Anderson]

Hi,

On Fri, May 9, 2025 at 6:13 AM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
> From: Steven Rostedt <rostedt@xxxxxxxxxxx>
>
> The per CPU "disabled" value was the original way to disable tracing when
> the tracing subsystem was first created. Today, the ring buffer
> infrastructure has its own way to disable tracing. In fact, things have
> changed so much since 2008 that many things ignore the disable flag.
>
> The kdb_ftdump() function iterates over all the current tracing CPUs and
> increments the "disabled" counter before doing the dump, and decrements it
> afterward.
>
> As the disabled flag can be ignored, doing this today is not reliable.
> Instead, simply call tracer_tracing_off() and then tracer_tracing_on() to
> disable and then enabled the entire ring buffer in one go!
>
> Cc: Jason Wessel <jason.wessel@xxxxxxxxxxxxx>
> Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Daniel Thompson <danielt@xxxxxxxxxx>
> Cc: Douglas Anderson <dianders@xxxxxxxxxxxx>
> Link: https://lore.kernel.org/20250505212235.549033722@xxxxxxxxxxx
> Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
> ---
>  kernel/trace/trace_kdb.c | 9 ++-------
>  1 file changed, 2 insertions(+), 7 deletions(-)

I'm not deeply familiar with the tracing system internals, but it
seems reasonable to me.

I did a quick sanity check and nothing went boom, too.

Reviewed-by: Douglas Anderson <dianders@xxxxxxxxxxxx>