[PATCH 32/36] ftrace: WARN on rcuidle

Peter Zijlstra
2022-06-08T14:52:11Z

CONFIG_GENERIC_ENTRY disallows any and all tracing when RCU isn't
enabled.

XXX if s390 (the only other GENERIC_ENTRY user as of this writing)
isn't comfortable with this, we could switch to
HAVE_NOINSTR_VALIDATION which is x86_64 only atm.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
include/linux/tracepoint.h | 13 ++++++++++++-
kernel/trace/trace.c | 3 +++
2 files changed, 15 insertions(+), 1 deletion(-)

--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -178,6 +178,16 @@ static inline struct tracepoint *tracepo
#endif /* CONFIG_HAVE_STATIC_CALL */

/*
+ * CONFIG_GENERIC_ENTRY archs are expected to have sanitized entry and idle
+ * code that disallow any/all tracing/instrumentation when RCU isn't watching.
+ */
+#ifdef CONFIG_GENERIC_ENTRY
+#define RCUIDLE_COND(rcuidle) (rcuidle)
+#else
+#define RCUIDLE_COND(rcuidle) (rcuidle && in_nmi())
+#endif
+
+/*
* it_func[0] is never NULL because there is at least one element in the array
* when the array itself is non NULL.
*/
@@ -189,7 +199,8 @@ static inline struct tracepoint *tracepo
return; \
\
/* srcu can't be used from NMI */ \
- WARN_ON_ONCE(rcuidle && in_nmi()); \
+ if (WARN_ON_ONCE(RCUIDLE_COND(rcuidle))) \
+ return; \
\
/* keep srcu and sched-rcu usage consistent */ \
preempt_disable_notrace(); \
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3104,6 +3104,9 @@ void __trace_stack(struct trace_array *t
return;
}

+ if (WARN_ON_ONCE(IS_ENABLED(CONFIG_GENERIC_ENTRY)))
+ return;
+
/*
* When an NMI triggers, RCU is enabled via rcu_nmi_enter(),
* but if the above rcu_is_watching() failed, then the NMI