markers: auto enable tracepoints (new API : trace_mark_tp())

Impact: new API

Add a new API trace_mark_tp(), which declares a marker within a
tracepoint probe. When the marker is activated, the tracepoint is
automatically enabled.

No branch test is used at the marker site, because it would be a
duplicate of the branch already present in the tracepoint.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 51 insertions, 2 deletions

diff --git a/kernel/marker.c b/kernel/marker.c
index 348e70cc355a..c14ec26a9b9f 100644
--- a/kernel/marker.c
+++ b/kernel/marker.c
@@ -479,7 +479,7 @@ static int marker_set_format(struct marker_entry *entry, const char *format)
 static int set_marker(struct marker_entry *entry, struct marker *elem,
                 int active)
 {
-        int ret;
+        int ret = 0;
         WARN_ON(strcmp(entry->name, elem->name) != 0);
 
         if (entry->format) {
@@ -531,9 +531,40 @@ static int set_marker(struct marker_entry *entry, struct marker *elem,
          */
         smp_wmb();
         elem->ptype = entry->ptype;
+
+        if (elem->tp_name && (active ^ elem->state)) {
+                WARN_ON(!elem->tp_cb);
+                /*
+                 * It is ok to directly call the probe registration because type
+                 * checking has been done in the __trace_mark_tp() macro.
+                 */
+
+                if (active) {
+                        /*
+                         * try_module_get should always succeed because we hold
+                         * lock_module() to get the tp_cb address.
+                         */
+                        ret = try_module_get(__module_text_address(
+                                (unsigned long)elem->tp_cb));
+                        BUG_ON(!ret);
+                        ret = tracepoint_probe_register_noupdate(
+                                elem->tp_name,
+                                elem->tp_cb);
+                } else {
+                        ret = tracepoint_probe_unregister_noupdate(
+                                elem->tp_name,
+                                elem->tp_cb);
+                        /*
+                         * tracepoint_probe_update_all() must be called
+                         * before the module containing tp_cb is unloaded.
+                         */
+                        module_put(__module_text_address(
+                                (unsigned long)elem->tp_cb));
+                }
+        }
         elem->state = active;
 
-        return 0;
+        return ret;
 }
 
 /*
@@ -544,7 +575,24 @@ static int set_marker(struct marker_entry *entry, struct marker *elem,
  */
 static void disable_marker(struct marker *elem)
 {
+        int ret;
+
         /* leave "call" as is. It is known statically. */
+        if (elem->tp_name && elem->state) {
+                WARN_ON(!elem->tp_cb);
+                /*
+                 * It is ok to directly call the probe registration because type
+                 * checking has been done in the __trace_mark_tp() macro.
+                 */
+                ret = tracepoint_probe_unregister_noupdate(elem->tp_name,
+                        elem->tp_cb);
+                WARN_ON(ret);
+                /*
+                 * tracepoint_probe_update_all() must be called
+                 * before the module containing tp_cb is unloaded.
+                 */
+                module_put(__module_text_address((unsigned long)elem->tp_cb));
+        }
         elem->state = 0;
         elem->single.func = __mark_empty_function;
         /* Update the function before setting the ptype */
@@ -608,6 +656,7 @@ static void marker_update_probes(void)
         marker_update_probe_range(__start___markers, __stop___markers);
         /* Markers in modules. */
         module_update_markers();
+        tracepoint_probe_update_all();
 }
 
 /**