[RFA][PATCH 4/4] tracing: Do not add event files for modules that fail tracepoints

[Steven Rostedt <rostedt@goodmis.org>]

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From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>

If a module fails to add its tracepoints due to module tainting, do not
create the module event infrastructure in the debugfs directory. As the events
will not work and worse yet, they will silently fail, making the user wonder
why the events they enable do not display anything.

Having a warning on module load and the events not visible to the users
will make the cause of the problem much clearer.

Fixes: 6d723736e472 "tracing/events: add support for modules to TRACE_EVENT"
Cc: stable@vger.kernel.org # 2.6.31+
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 include/linux/tracepoint.h  | 7 +++++++
 kernel/trace/trace_events.c | 4 ++++
 kernel/tracepoint.c         | 2 +-
 3 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index accc497..3cb2842 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -16,6 +16,7 @@
 
 #include <linux/errno.h>
 #include <linux/types.h>
+#include <linux/module.h>
 #include <linux/rcupdate.h>
 #include <linux/static_key.h>
 
@@ -60,6 +61,12 @@ struct tp_module {
 	unsigned int num_tracepoints;
 	struct tracepoint * const *tracepoints_ptrs;
 };
+static inline bool trace_module_has_bad_taint(struct module *mod)
+{
+	return mod->taints & ~((1 << TAINT_OOT_MODULE) | (1 << TAINT_CRAP));
+}
+#else
+#define trace_module_has_bad_taint(mod) ({false;})
 #endif /* CONFIG_MODULES */
 
 struct tracepoint_iter {
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index e71ffd4..b2fee73 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -1777,6 +1777,10 @@ static void trace_module_add_events(struct module *mod)
 {
 	struct ftrace_event_call **call, **start, **end;
 
+	/* Don't add infrastructure for mods without tracepoints */
+	if (trace_module_has_bad_taint(mod))
+		return;
+
 	start = mod->trace_events;
 	end = mod->trace_events + mod->num_trace_events;
 
diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index 8a5d5e95..f74e953 100644
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -644,7 +644,7 @@ 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)) {
 		pr_err("Module '%s' is tainted, disabling tracepoints\n",
 		       mod->name);
 		return 0;
-- 
1.8.5.3