[RFC PATCH v4 2/4] tracing: Introduce tracepoint_is_faultable()

[Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>]

Introduce a "faultable" flag within the extended structure to know
whether a tracepoint needs rcu tasks trace grace period before reclaim.
This can be queried using tracepoint_is_faultable().

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: Michael Jeanson <mjeanson@xxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
Cc: Yonghong Song <yhs@xxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx>
Cc: bpf@xxxxxxxxxxxxxxx
Cc: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>
Cc: Jordan Rife <jrife@xxxxxxxxxx>
---
 include/linux/tracepoint-defs.h |  2 ++
 include/linux/tracepoint.h      | 24 ++++++++++++++++++++++++
 include/trace/define_trace.h    |  2 +-
 3 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/include/linux/tracepoint-defs.h b/include/linux/tracepoint-defs.h
index 967c08d9da84..aebf0571c736 100644
--- a/include/linux/tracepoint-defs.h
+++ b/include/linux/tracepoint-defs.h
@@ -32,6 +32,8 @@ struct tracepoint_func {
 struct tracepoint_ext {
 	int (*regfunc)(void);
 	void (*unregfunc)(void);
+	/* Flags. */
+	unsigned int faultable:1;
 };
 
 struct tracepoint {
diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index 83dc24ee8b13..259f0ab4ece6 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -104,6 +104,12 @@ void for_each_tracepoint_in_module(struct module *mod,
  * tracepoint_synchronize_unregister must be called between the last tracepoint
  * probe unregistration and the end of module exit to make sure there is no
  * caller executing a probe when it is freed.
+ *
+ * An alternative is to use the following for batch reclaim associated
+ * with a given tracepoint:
+ *
+ * - tracepoint_is_faultable() == false: call_rcu()
+ * - tracepoint_is_faultable() == true:  call_rcu_tasks_trace()
  */
 #ifdef CONFIG_TRACEPOINTS
 static inline void tracepoint_synchronize_unregister(void)
@@ -111,9 +117,17 @@ static inline void tracepoint_synchronize_unregister(void)
 	synchronize_rcu_tasks_trace();
 	synchronize_rcu();
 }
+static inline bool tracepoint_is_faultable(struct tracepoint *tp)
+{
+	return tp->ext && tp->ext->faultable;
+}
 #else
 static inline void tracepoint_synchronize_unregister(void)
 { }
+static inline bool tracepoint_is_faultable(struct tracepoint *tp)
+{
+	return false;
+}
 #endif
 
 #ifdef CONFIG_HAVE_SYSCALL_TRACEPOINTS
@@ -345,6 +359,15 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
 	struct tracepoint_ext __tracepoint_ext_##_name = {		\
 		.regfunc = _reg,					\
 		.unregfunc = _unreg,					\
+		.faultable = false,					\
+	};								\
+	__DEFINE_TRACE_EXT(_name, &__tracepoint_ext_##_name, PARAMS(_proto), PARAMS(_args));
+
+#define DEFINE_TRACE_SYSCALL(_name, _reg, _unreg, _proto, _args)	\
+	struct tracepoint_ext __tracepoint_ext_##_name = {		\
+		.regfunc = _reg,					\
+		.unregfunc = _unreg,					\
+		.faultable = true,					\
 	};								\
 	__DEFINE_TRACE_EXT(_name, &__tracepoint_ext_##_name, PARAMS(_proto), PARAMS(_args));
 
@@ -389,6 +412,7 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
 #define __DECLARE_TRACE_SYSCALL	__DECLARE_TRACE
 
 #define DEFINE_TRACE_FN(name, reg, unreg, proto, args)
+#define DEFINE_TRACE_SYSCALL(name, reg, unreg, proto, args)
 #define DEFINE_TRACE(name, proto, args)
 #define EXPORT_TRACEPOINT_SYMBOL_GPL(name)
 #define EXPORT_TRACEPOINT_SYMBOL(name)
diff --git a/include/trace/define_trace.h b/include/trace/define_trace.h
index ff5fa17a6259..63fea2218afa 100644
--- a/include/trace/define_trace.h
+++ b/include/trace/define_trace.h
@@ -48,7 +48,7 @@
 
 #undef TRACE_EVENT_SYSCALL
 #define TRACE_EVENT_SYSCALL(name, proto, args, struct, assign, print, reg, unreg) \
-	DEFINE_TRACE_FN(name, reg, unreg, PARAMS(proto), PARAMS(args))
+	DEFINE_TRACE_SYSCALL(name, reg, unreg, PARAMS(proto), PARAMS(args))
 
 #undef TRACE_EVENT_NOP
 #define TRACE_EVENT_NOP(name, proto, args, struct, assign, print)
-- 
2.39.5