[PATCH v2 25/40] tracing: Add support for dynamic tracepoints

[Tom Zanussi]

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 <tom.zanu...@linux.intel.com>
---
 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
-- 
1.9.3