Hi Mathieu,

On Tue, 2017-09-05 at 23:29 +0000, Mathieu Desnoyers wrote:

----- On Sep 5, 2017, at 5:57 PM, Tom Zanussi tom.zanussi@linux.intel.com wrote:

quoted

The tracepoint infrastructure assumes statically-defined tracepoints
and uses static_keys for tracepoint enablement.  In order to define
tracepoints on the fly, we need to have a dynamic counterpart.

Add a 'dynamic' flag to struct tracepoint along with accompanying
logic for this purpose.

Signed-off-by: Tom Zanussi <redacted>
---
include/linux/tracepoint-defs.h |  1 +
kernel/tracepoint.c             | 18 +++++++++++++-----
2 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/include/linux/tracepoint-defs.h b/include/linux/tracepoint-defs.h
index a031920..bc22d54 100644
--- a/include/linux/tracepoint-defs.h
+++ b/include/linux/tracepoint-defs.h

@@ -32,6 +32,7 @@ struct tracepoint {

	int (*regfunc)(void);
	void (*unregfunc)(void);
	struct tracepoint_func __rcu *funcs;
+	bool dynamic;
};

#endif

diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index 685c50a..1c5957f 100644
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c

@@ -197,7 +197,9 @@ static int tracepoint_add_func(struct tracepoint *tp,

	struct tracepoint_func *old, *tp_funcs;
	int ret;

-	if (tp->regfunc && !static_key_enabled(&tp->key)) {
+	if (tp->regfunc &&
+	    ((tp->dynamic && !(atomic_read(&tp->key.enabled) > 0)) ||
+	     !static_key_enabled(&tp->key))) {
		ret = tp->regfunc();
		if (ret < 0)
			return ret;

@@ -219,7 +221,9 @@ static int tracepoint_add_func(struct tracepoint *tp,

	 * is used.
	 */
	rcu_assign_pointer(tp->funcs, tp_funcs);
-	if (!static_key_enabled(&tp->key))
+	if (tp->dynamic && !(atomic_read(&tp->key.enabled) > 0))
+		atomic_inc(&tp->key.enabled);
+	else if (!tp->dynamic && !static_key_enabled(&tp->key))
		static_key_slow_inc(&tp->key);
	release_probes(old);
	return 0;

@@ -246,10 +250,14 @@ static int tracepoint_remove_func(struct tracepoint *tp,

	if (!tp_funcs) {
		/* Removed last function */
-		if (tp->unregfunc && static_key_enabled(&tp->key))
+		if (tp->unregfunc &&
+		    ((tp->dynamic && (atomic_read(&tp->key.enabled) > 0)) ||
+		     static_key_enabled(&tp->key)))
			tp->unregfunc();

-		if (static_key_enabled(&tp->key))
+		if (tp->dynamic && (atomic_read(&tp->key.enabled) > 0))
+			atomic_dec(&tp->key.enabled);
+		else if (!tp->dynamic && static_key_enabled(&tp->key))
			static_key_slow_dec(&tp->key);
	}
	rcu_assign_pointer(tp->funcs, tp_funcs);

@@ -258,7 +266,7 @@ static int tracepoint_remove_func(struct tracepoint *tp,

}

/**
- * tracepoint_probe_register -  Connect a probe to a tracepoint
+ * tracepoint_probe_register_prio -  Connect a probe to a tracepoint
 * @tp: tracepoint
 * @probe: probe handler
 * @data: tracepoint data

Hi Tom,

Thanks for updating your approach to dynamic tracepoints.

Since you're fixing up this comment above tracepoint_probe_register_prio,
can you also remove the following line above tracepoint_probe_register
while you are at it ?

Sure, will do.

Thanks,

Tom