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

[Steven Rostedt]

From: David Carlier <devnexen@xxxxxxxxx>

The trace_##name##_enabled() static call branch is used when work needs to
be done for a tracepoint. It allows that work to be skipped when the
tracepoint is not active and still uses the static_branch() of the
tracepoint to keep performance.

Tracepoints themselves require being called in "RCU watching" locations
otherwise races can occur that corrupts things. In order to make sure
lockdep triggers at tracepoint locations, the lockdep checks are added to
the tracepoint calling location and trigger even if the tracepoint is not
enabled. This is done because a poorly placed tracepoint may never be
detected if it is never enabled when lockdep is enabled.

As trace_##name##_enabled() also prevents the lockdep checks when the
tracepoint is disabled add lockdep checks to that as well so that if one
is placed in a location that RCU is not watching, it will trigger a
lockdep splat even when the tracepoint is not enabled.

Cc: Vineeth Pillai (Google) <vineeth@xxxxxxxxxxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: https://patch.msgid.link/20260430144159.10985-1-devnexen@xxxxxxxxx
Signed-off-by: David Carlier <devnexen@xxxxxxxxx>
[ Updated the change log ]
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
 include/linux/tracepoint.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index 763eea4d80d8..c29fc57392bb 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);\
 	}
 
-- 
2.53.0