[for-next][PATCH 04/15] tracepoint: Add lockdep rcu_is_watching() check to trace_##name##_enabled()

[Geert Uytterhoeven]

Hi Steven,

On Tue, 30 Jun 2026 at 21:53, Steven Rostedt <rostedt at kernel.org> wrote:
> On Tue, 30 Jun 2026 19:39:02 +0200
> Geert Uytterhoeven <geert at linux-m68k.org> wrote:
> > Other Renesas ARM32 platforms I tried (R-Mobile A1, RZ/A1H, RZ/A2M)
> > are unafffected, perhaps because they are not SMP?
> > All Renesas ARM64 platforms I tried (R-Car Gen3/4) are also unaffected.
> >
> > Reverting the commit fixes the issue.
> >
> > Do you have a clue?
>
> Yes, it means the code was buggy before the commit. The commit will trigger
> warnings in places that have issues. Before the commit, the buggy code was
> never caught.
>
> It's like enabling KASAN and finding code that has use-after-free.
> Disabling KASAN is not the fix.
>
> Tracepoints are managed by using RCU. There's places that RCU is turned
> off, meaning a tracepoint in one of those locations can be triggered when
> RCU is not active which may have a use-after-free semantic when the
> tracepoint is enabled.
>
> Tracepoints hidden by trace_#tracepoint#_enabled() are not caught when RCU
> is disabled and the tracepoint is not active. This commit makes these
> locations trigger even when the tracepoint is not active.

Sorry, my wording could indeed be better: this commit probably does not
"cause" the issue, but merely exposes it.

> One way to find out if this is an existing bug or not, could you enable the
> preemptirq tracepoints and run the tests again with the commit reverted?
>
>   echo 1 >  /sys/kernel/tracing/events/preemptirq/enable
>
> This will enable the events that are hidden without the commit. If it
> triggers when enabled, it shows the commit found a bug.
>
> If you get the same errors, the bug isn't with the commit in question, it's
> with the tracepoints being called during suspend/resume. We will need to
> fix that if that's the case.

Thanks, it does not trigger with the commit reverted and the "echo 1 > ...".

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

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