From: "Steven Rostedt (Google)" <rostedt@goodmis.org>
There are two WARN_ON*() warnings in tracepoint.h that deal with RCU
usage. But when they trigger, especially from using a TRACE_EVENT()
macro, the information is not very helpful and is confusing:
------------[ cut here ]------------
WARNING: CPU: 0 PID: 0 at include/trace/events/lock.h:24 lock_acquire+0x2b2/0x2d0
Where the above warning takes you to:
TRACE_EVENT(lock_acquire, <<<--- line 24 in lock.h
TP_PROTO(struct lockdep_map *lock, unsigned int subclass,
int trylock, int read, int check,
struct lockdep_map *next_lock, unsigned long ip),
[..]
Change the WARN_ON_ONCE() to WARN_ONCE() and add a string that allows
someone to search for exactly where the bug happened.
Link: https://lore.kernel.org/linux-trace-kernel/20240228133112.0d64fb1b@gandalf.local.home
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Reported-by: Borislav Petkov <bp@alien8.de>
Tested-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
include/linux/tracepoint.h | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index 88c0ba623ee6..689b6d71590e 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -199,7 +199,8 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
if (!(cond)) \
return; \
\
- if (WARN_ON_ONCE(RCUIDLE_COND(rcuidle))) \
+ if (WARN_ONCE(RCUIDLE_COND(rcuidle), \
+ "Bad RCU usage for tracepoint")) \
return; \
\
/* keep srcu and sched-rcu usage consistent */ \
@@ -259,7 +260,8 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
TP_ARGS(args), \
TP_CONDITION(cond), 0); \
if (IS_ENABLED(CONFIG_LOCKDEP) && (cond)) { \
- WARN_ON_ONCE(!rcu_is_watching()); \
+ WARN_ONCE(!rcu_is_watching(), \
+ "RCU not watching for tracepoint"); \
} \
} \
__DECLARE_TRACE_RCU(name, PARAMS(proto), PARAMS(args), \
--
2.43.0