From: Steven Rostedt <[email protected]>
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 <[email protected]>
Closes:
https://lore.kernel.org/all/camuhmdxud_rpwag_hfqa2bybgrxg6knxgl1obcwzrptsk3t...@mail.gmail.com/
Fixes: 9764e731ef6ab ("tracepoint: Add lockdep rcu_is_watching() check to
trace_##name##_enabled()")
Signed-off-by: Steven Rostedt <[email protected]>
---
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
