Re: [PATCH] tracing: Add a no-rcu-check version of trace_##event##_enabled()

[Geert Uytterhoeven]

On Wed, 1 Jul 2026 at 19:27, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> From: Steven Rostedt <rostedt@xxxxxxxxxxx>
>
> Tracepoints require that RCU is watching. To prevent them from being used
> in places that RCU is not watching, the trace_##event() macro always
> calls rcu_is_watching() even when the event is not enabled and warns if
> RCU is not watching. This is to make sure a warning is triggered even if
> the tracepoint is never enabled (as it is only a bug when it is).
>
> It was noticed that tracepoints could be hidden within
> trace_#event#_enabled() calls, which are used to do extra work for the
> tracepoint only if the tracepoint is enabled. But this also can hide the
> fact that a tracepoint is placed in a location that can be called when RCU
> is not watching.
>
> Commit 9764e731ef6ab ("tracepoint: Add lockdep rcu_is_watching() check to
> trace_##name##_enabled()") added a check to the trace_##event##_enabled()
> macro to make sure RCU is watching when it is called to make sure not to
> hide the bug of a tracepoint being called when RCU is not watching.
>
> There is one case in the irq_disable tracepoint where it is within a
> trace_irq_disable_enabled() block, but it checks if RCU is watching, and
> if it isn't, it makes a call to ct_irq_enter() that makes RCU watch again.
> But because trace_irq_disable_enabled() now checks if RCU is watching and
> will trigger if it isn't. This is a false warning as the code within
> the block handles this case.
>
> Add a new internal macro __trace_##event##_enabled() that doesn't check if
> RCU is watching, and convert the irq_enable/disable tracepoints over to
> it.
>
> Reported-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> Closes: https://lore.kernel.org/all/CAMuHMdXud_RpWag_hFqa2ByBGRxg6KnxGL1ObCWZrpTsk3TfAw@xxxxxxxxxxxxxx/
> Fixes: 9764e731ef6ab ("tracepoint: Add lockdep rcu_is_watching() check to trace_##name##_enabled()")
> Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>

Thanks, warning gone on all affected platforms.
Tested-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds