In the past, I've had lots of reports about trace events not working.

Developers would say they put a trace_printk() before and after the trace
 event but when they enable it (and the trace event said it was enabled) they
 would see the trace_printks but not the trace event.
 
 I was not able to reproduce this, but that's because I wasn't looking at
 the right location. Recently, another bug came up that showed the issue.
 
 If your kernel supports signed modules but allows for non-signed modules
 to be loaded, then when one is, the kernel will silently set the
 MODULE_FORCED taint on the module. Although, this taint happens without
 the need for insmod --force or anything of the kind, it labels the
 module with that taint anyway.
 
 If this tainted module has tracepoints, the tracepoints will be ignored
 because of the MODULE_FORCED taint. But no error message will be
 displayed. Worse yet, the event infrastructure will still be created
 letting users enable the trace event represented by the tracepoint,
 although that event will never actually be enabled. This is because
 the tracepoint infrastructure allows for non-existing tracepoints to
 be enabled for new modules to arrive and have their tracepoints set.
 
 Although there are several things wrong with the above, this change
 only addresses the creation of the trace event files for tracepoints
 that are not created when a module is loaded and is tainted. This change
 will print an error message about the module being tainted and not the
 trace events will not be created, and it does not create the trace event
 infrastructure.
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Merge tag 'trace-fixes-v3.14-rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull tracing fix from Steven Rostedt:
 "In the past, I've had lots of reports about trace events not working.
  Developers would say they put a trace_printk() before and after the
  trace event but when they enable it (and the trace event said it was
  enabled) they would see the trace_printks but not the trace event.

  I was not able to reproduce this, but that's because I wasn't looking
  at the right location.  Recently, another bug came up that showed the
  issue.

  If your kernel supports signed modules but allows for non-signed
  modules to be loaded, then when one is, the kernel will silently set
  the MODULE_FORCED taint on the module.  Although, this taint happens
  without the need for insmod --force or anything of the kind, it labels
  the module with that taint anyway.

  If this tainted module has tracepoints, the tracepoints will be
  ignored because of the MODULE_FORCED taint.  But no error message will
  be displayed.  Worse yet, the event infrastructure will still be
  created letting users enable the trace event represented by the
  tracepoint, although that event will never actually be enabled.  This
  is because the tracepoint infrastructure allows for non-existing
  tracepoints to be enabled for new modules to arrive and have their
  tracepoints set.

  Although there are several things wrong with the above, this change
  only addresses the creation of the trace event files for tracepoints
  that are not created when a module is loaded and is tainted.  This
  change will print an error message about the module being tainted and
  not the trace events will not be created, and it does not create the
  trace event infrastructure"

* tag 'trace-fixes-v3.14-rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  tracing: Do not add event files for modules that fail tracepoints

include/linux/tracepoint.h

@@ -60,6 +60,12 @@ struct tp_module {
 	unsigned int num_tracepoints;
 	struct tracepoint * const *tracepoints_ptrs;
 };
+bool trace_module_has_bad_taint(struct module *mod);
+#else
+static inline bool trace_module_has_bad_taint(struct module *mod)
+{
+	return false;
+}
 #endif /* CONFIG_MODULES */
 
 struct tracepoint_iter {

kernel/trace/trace_events.c

@@ -1777,6 +1777,16 @@ static void trace_module_add_events(struct module *mod)
 {
 	struct ftrace_event_call **call, **start, **end;
 
+	if (!mod->num_trace_events)
+		return;
+
+	/* Don't add infrastructure for mods without tracepoints */
+	if (trace_module_has_bad_taint(mod)) {
+		pr_err("%s: module has bad taint, not creating trace events\n",
+		       mod->name);
+		return;
+	}
+
 	start = mod->trace_events;
 	end = mod->trace_events + mod->num_trace_events;
 

kernel/tracepoint.c

@@ -631,6 +631,11 @@ void tracepoint_iter_reset(struct tracepoint_iter *iter)
 EXPORT_SYMBOL_GPL(tracepoint_iter_reset);
 
 #ifdef CONFIG_MODULES
+bool trace_module_has_bad_taint(struct module *mod)
+{
+	return mod->taints & ~((1 << TAINT_OOT_MODULE) | (1 << TAINT_CRAP));
+}
+
 static int tracepoint_module_coming(struct module *mod)
 {
 	struct tp_module *tp_mod, *iter;
@@ -641,7 +646,7 @@ static int tracepoint_module_coming(struct module *mod)
 	 * module headers (for forced load), to make sure we don't cause a crash.
 	 * Staging and out-of-tree GPL modules are fine.
 	 */
-	if (mod->taints & ~((1 << TAINT_OOT_MODULE) | (1 << TAINT_CRAP)))
+	if (trace_module_has_bad_taint(mod))
 		return 0;
 	mutex_lock(&tracepoints_mutex);
 	tp_mod = kmalloc(sizeof(struct tp_module), GFP_KERNEL);