tracing: Add 'stacktrace' event trigger command

Add 'stacktrace' event_command.  stacktrace event triggers are added
by the user via this command in a similar way and using practically
the same syntax as the analogous 'stacktrace' ftrace function command,
but instead of writing to the set_ftrace_filter file, the stacktrace
event trigger is written to the per-event 'trigger' files:

    echo 'stacktrace' > .../tracing/events/somesys/someevent/trigger

The above command will turn on stacktraces for someevent i.e. whenever
someevent is hit, a stacktrace will be logged.

This also adds a 'count' version that limits the number of times the
command will be invoked:

    echo 'stacktrace:N' > .../tracing/events/somesys/someevent/trigger

Where N is the number of times the command will be invoked.

The above command will log N stacktraces for someevent i.e. whenever
someevent is hit N times, a stacktrace will be logged.

Link: http://lkml.kernel.org/r/0c30c008a0828c660aa0e1bbd3255cf179ed5c30.1382622043.git.tom.zanussi@linux.intel.com

Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 79 insertions, 0 deletions

diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c
index d775c3da180f..a3bd1da90c56 100644
--- a/kernel/trace/trace_events_trigger.c
+++ b/kernel/trace/trace_events_trigger.c
@@ -780,6 +780,84 @@ static __init int register_trigger_snapshot_cmd(void)
 static __init int register_trigger_snapshot_cmd(void) { return 0; }
 #endif /* CONFIG_TRACER_SNAPSHOT */
 
+#ifdef CONFIG_STACKTRACE
+/*
+ * Skip 3:
+ *   stacktrace_trigger()
+ *   event_triggers_post_call()
+ *   ftrace_raw_event_xxx()
+ */
+#define STACK_SKIP 3
+
+static void
+stacktrace_trigger(struct event_trigger_data *data)
+{
+        trace_dump_stack(STACK_SKIP);
+}
+
+static void
+stacktrace_count_trigger(struct event_trigger_data *data)
+{
+        if (!data->count)
+                return;
+
+        if (data->count != -1)
+                (data->count)--;
+
+        stacktrace_trigger(data);
+}
+
+static int
+stacktrace_trigger_print(struct seq_file *m, struct event_trigger_ops *ops,
+                         struct event_trigger_data *data)
+{
+        return event_trigger_print("stacktrace", m, (void *)data->count,
+                                   data->filter_str);
+}
+
+static struct event_trigger_ops stacktrace_trigger_ops = {
+        .func                   = stacktrace_trigger,
+        .print                  = stacktrace_trigger_print,
+        .init                   = event_trigger_init,
+        .free                   = event_trigger_free,
+};
+
+static struct event_trigger_ops stacktrace_count_trigger_ops = {
+        .func                   = stacktrace_count_trigger,
+        .print                  = stacktrace_trigger_print,
+        .init                   = event_trigger_init,
+        .free                   = event_trigger_free,
+};
+
+static struct event_trigger_ops *
+stacktrace_get_trigger_ops(char *cmd, char *param)
+{
+        return param ? &stacktrace_count_trigger_ops : &stacktrace_trigger_ops;
+}
+
+static struct event_command trigger_stacktrace_cmd = {
+        .name                   = "stacktrace",
+        .trigger_type           = ETT_STACKTRACE,
+        .post_trigger           = true,
+        .func                   = event_trigger_callback,
+        .reg                    = register_trigger,
+        .unreg                  = unregister_trigger,
+        .get_trigger_ops        = stacktrace_get_trigger_ops,
+};
+
+static __init int register_trigger_stacktrace_cmd(void)
+{
+        int ret;
+
+        ret = register_event_command(&trigger_stacktrace_cmd);
+        WARN_ON(ret < 0);
+
+        return ret;
+}
+#else
+static __init int register_trigger_stacktrace_cmd(void) { return 0; }
+#endif /* CONFIG_STACKTRACE */
+
 static __init void unregister_trigger_traceon_traceoff_cmds(void)
 {
         unregister_event_command(&trigger_traceon_cmd);
@@ -804,6 +882,7 @@ __init int register_trigger_cmds(void)
 {
         register_trigger_traceon_traceoff_cmds();
         register_trigger_snapshot_cmd();
+        register_trigger_stacktrace_cmd();
 
         return 0;
 }