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

[Steven Rostedt <rostedt@goodmis.org>]

From: Steven Rostedt <rostedt@goodmis.org>

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@linux-m68k.org>
Closes: https://lore.kernel.org/all/CAMuHMdXud_RpWag_hFqa2ByBGRxg6KnxGL1ObCWZrpTsk3TfAw@mail.gmail.com/
Fixes: 9764e731ef6ab ("tracepoint: Add lockdep rcu_is_watching() check to trace_##name##_enabled()")
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 include/linux/tracepoint.h      | 12 +++++++++++-
 kernel/trace/trace_preemptirq.c |  2 +-
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index 4a0c36f40fe2..e0d838c9ce93 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -292,13 +292,18 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
 	{								\
 	}								\
 	static inline bool						\
+	__trace_##name##_enabled(void)					\
+	{								\
+		return static_branch_unlikely(&__tracepoint_##name.key);\
+	}								\
+	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);\
+		return __trace_##name##_enabled();			\
 	}
 
 #define __DECLARE_TRACE(name, proto, args, cond, data_proto)			\
@@ -457,6 +462,11 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
 	{								\
 	}								\
 	static inline bool						\
+	__trace_##name##_enabled(void)					\
+	{								\
+		return false;						\
+	}								\
+	static inline bool						\
 	trace_##name##_enabled(void)					\
 	{								\
 		return false;						\
diff --git a/kernel/trace/trace_preemptirq.c b/kernel/trace/trace_preemptirq.c
index 0c42b15c3800..b63e3558948f 100644
--- a/kernel/trace/trace_preemptirq.c
+++ b/kernel/trace/trace_preemptirq.c
@@ -30,7 +30,7 @@
 #else
 #define trace(point, args)					\
 	do {							\
-		if (trace_##point##_enabled()) {		\
+		if (__trace_##point##_enabled()) {		\
 			bool exit_rcu = false;			\
 			if (in_nmi())				\
 				break;				\
-- 
2.53.0