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>

3 files changed, 96 insertions, 3 deletions

diff --git a/include/linux/marker.h b/include/linux/marker.h
index 05ec0df37089..57a307018ceb 100644
--- a/include/linux/marker.h
+++ b/include/linux/marker.h
@@ -49,6 +49,8 @@ struct marker {
         void (*call)(const struct marker *mdata, void *call_private, ...);
         struct marker_probe_closure single;
         struct marker_probe_closure *multi;
+        const char *tp_name;    /* Optional tracepoint name */
+        void *tp_cb;            /* Optional tracepoint callback */
 } __attribute__((aligned(8)));
 
 #ifdef CONFIG_MARKERS
@@ -73,7 +75,7 @@ struct marker {
                 __attribute__((section("__markers"), aligned(8))) =     \
                 { __mstrtab_##name, &__mstrtab_##name[sizeof(#name)],   \
                 0, 0, marker_probe_cb,                                  \
-                { __mark_empty_function, NULL}, NULL };                 \
+                { __mark_empty_function, NULL}, NULL, NULL, NULL };     \
                 __mark_check_format(format, ## args);                   \
                 if (unlikely(__mark_##name.state)) {                    \
                         (*__mark_##name.call)                           \
@@ -81,11 +83,38 @@ struct marker {
                 }                                                       \
         } while (0)
 
+#define __trace_mark_tp(name, call_private, tp_name, tp_cb, format, args...) \
+        do {                                                            \
+                void __check_tp_type(void)                              \
+                {                                                       \
+                        register_trace_##tp_name(tp_cb);                \
+                }                                                       \
+                static const char __mstrtab_##name[]                    \
+                __attribute__((section("__markers_strings")))           \
+                = #name "\0" format;                                    \
+                static struct marker __mark_##name                      \
+                __attribute__((section("__markers"), aligned(8))) =     \
+                { __mstrtab_##name, &__mstrtab_##name[sizeof(#name)],   \
+                0, 0, marker_probe_cb,                                  \
+                { __mark_empty_function, NULL}, NULL, #tp_name, tp_cb };\
+                __mark_check_format(format, ## args);                   \
+                (*__mark_##name.call)(&__mark_##name, call_private,     \
+                                        ## args);                       \
+        } while (0)
+
 extern void marker_update_probe_range(struct marker *begin,
         struct marker *end);
 #else /* !CONFIG_MARKERS */
 #define __trace_mark(generic, name, call_private, format, args...) \
                 __mark_check_format(format, ## args)
+#define __trace_mark_tp(name, call_private, tp_name, tp_cb, format, args...) \
+        do {                                                            \
+                void __check_tp_type(void)                              \
+                {                                                       \
+                        register_trace_##tp_name(tp_cb);                \
+                }                                                       \
+                __mark_check_format(format, ## args);                   \
+        } while (0)
 static inline void marker_update_probe_range(struct marker *begin,
         struct marker *end)
 { }
@@ -118,6 +147,20 @@ static inline void marker_update_probe_range(struct marker *begin,
         __trace_mark(1, name, NULL, format, ## args)
 
 /**
+ * trace_mark_tp - Marker in a tracepoint callback
+ * @name: marker name, not quoted.
+ * @tp_name: tracepoint name, not quoted.
+ * @tp_cb: tracepoint callback. Should have an associated global symbol so it
+ *         is not optimized away by the compiler (should not be static).
+ * @format: format string
+ * @args...: variable argument list
+ *
+ * Places a marker in a tracepoint callback.
+ */
+#define trace_mark_tp(name, tp_name, tp_cb, format, args...)    \
+        __trace_mark_tp(name, NULL, tp_name, tp_cb, format, ## args)
+
+/**
  * MARK_NOARGS - Format string for a marker with no argument.
  */
 #define MARK_NOARGS " "
diff --git a/init/Kconfig b/init/Kconfig
index 86b00c53fade..f5bacb438711 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -808,6 +808,7 @@ config TRACEPOINTS
 
 config MARKERS
         bool "Activate markers"
+        depends on TRACEPOINTS
         help
           Place an empty function call at each marker site. Can be
           dynamically changed for a probe function.
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();
 }
 
 /**