Re: [PATCH v2] tracepoint: add lockdep rcu_is_watching() check to trace_##name##_enabled()

[Steven Rostedt <rostedt@goodmis.org>]

On Thu, 30 Apr 2026 15:41:59 +0100
David Carlier <devnexen@gmail.com> wrote:

> trace_call__##name() was added by commit 677a3d82b640 ("tracepoint: Add
> trace_call__##name() API") for callers that already gate on
> trace_##name##_enabled(), letting them skip the redundant
> static_branch_unlikely() re-evaluation. The LOCKDEP rcu_is_watching()
> WARN_ONCE() that trace_##name() carries on the disabled path was not
> mirrored, so the cold-path coverage added by commit c2679254b9c9
> ("tracing: Make tracepoint lockdep check actually test something") is
> lost for trace_call__##name() callers when the tracepoint is disabled.
> 
> When the tracepoint is enabled, the rcu_dereference inside
> __DO_TRACE_CALL() already trips under PROVE_RCU, so the warning is
> only needed on the !enabled path. The natural place is the gate that
> trace_call__##name() callers consult: trace_##name##_enabled().
> 
> Fixes: 677a3d82b640 ("tracepoint: Add trace_call__##name() API")

Thanks, but I'm 86'ing the Fixes tag. The above commit has absolutely
nothing to do with this patch. This issue was there from the beginning of
having the trace_*_enabled() macro. This isn't a fix.

I'll modify the change log to be more accurate as well.

-- Steve


> Cc: Vineeth Pillai (Google) <vineeth@bitbyteword.org>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> Cc: Masami Hiramatsu <mhiramat@kernel.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: David Carlier <devnexen@gmail.com>
> ---
>  include/linux/tracepoint.h | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> index 578e520b6ee6..3b3ab19c2627 100644
> --- a/include/linux/tracepoint.h
> +++ b/include/linux/tracepoint.h
> @@ -293,6 +293,10 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
>  	static inline bool						\
>  	trace_##name##_enabled(void)					\
>  	{								\
> +		if (IS_ENABLED(CONFIG_LOCKDEP)) {			\
> +			WARN_ONCE(!rcu_is_watching(),			\
> +				  "RCU not watching for tracepoint");	\
> +		}							\
>  		return static_branch_unlikely(&__tracepoint_##name.key);\
>  	}
>