[PATCH] tracepoint: add lockdep rcu_is_watching() check to trace_call__##name()

[David Carlier <devnexen@gmail.com>]

trace_call__##name() was added by commit 677a3d82b640 ("tracepoint: Add
trace_call__##name() API") to let callers that already gate on
trace_##name##_enabled() skip the redundant static_branch_unlikely()
re-evaluation. The changelog states that the new helper retains the
LOCKDEP RCU-watching assertion carried by trace_##name(), but the
WARN_ONCE() was omitted from both definitions.

Without it, sites converted from trace_foo(args) to trace_call__foo(args)
lose the WARN_ONCE(!rcu_is_watching()) coverage under CONFIG_LOCKDEP when
the tracepoint is enabled - the case that commit c2679254b9c9 ("tracing:
Make tracepoint lockdep check actually test something") added the warning
for.

Mirror the same block in both trace_call__##name() bodies, gated by
(cond) in __DECLARE_TRACE to match its trace_##name() and ungated in
__DECLARE_TRACE_SYSCALL.

Fixes: 677a3d82b640 ("tracepoint: Add trace_call__##name() API")
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 | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index 578e520b6ee6..048e0035d4fa 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -318,6 +318,10 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
 	static inline void trace_call__##name(proto)			\
 	{								\
 		__do_trace_##name(args);				\
+		if (IS_ENABLED(CONFIG_LOCKDEP) && (cond)) {		\
+			WARN_ONCE(!rcu_is_watching(),			\
+				  "RCU not watching for tracepoint");	\
+		}							\
 	}
 
 #define __DECLARE_TRACE_SYSCALL(name, proto, args, data_proto)		\
@@ -342,6 +346,10 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
 	{								\
 		might_fault();						\
 		__do_trace_##name(args);				\
+		if (IS_ENABLED(CONFIG_LOCKDEP)) {			\
+			WARN_ONCE(!rcu_is_watching(),			\
+				  "RCU not watching for tracepoint");	\
+		}							\
 	}
 
 /*
-- 
2.53.0