tracing: Introduce tracepoint_is_faultable()

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().

Acked-by: Andrii Nakryiko <andrii@kernel.org>
Tested-by: Jordan Rife <jrife@google.com>
Cc: Michael Jeanson <mjeanson@efficios.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Yonghong Song <yhs@fb.com>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: bpf@vger.kernel.org
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Jordan Rife <jrife@google.com>
Cc: linux-trace-kernel@vger.kernel.org
Link: https://lore.kernel.org/20241031152056.744137-3-mathieu.desnoyers@efficios.com
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Author: compudj

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 {

include/linux/tracepoint.h

@@ -104,16 +104,30 @@ 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)
 {
 	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)
 	static 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)	\
+	static 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)

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)