[PATCH 2/3] tracing/profile: add ref count for registering profile events

[Steven Rostedt <rostedt@goodmis.org>]

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From: Steven Rostedt <srostedt@redhat.com>

Li Zefan discovered that doing the following:

 # insmod trace-events-sample.ko
 # perf record -f -a -e sample:foo_bar sleep 3 &
 # sleep 1
 # rmmod trace_events_sample
 # insmod trace-events-sample.ko

Would cause an OOPS. This was because the registering of the profiler
registers inside the module and does not unregister when unloaded.

This patch adds an increment of the module refcount when a profile
registers a tracepoint, to prevent a module from being unloaded
while being profiled.

Reported-by: Li Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <4A9214E3.2070807@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 include/trace/ftrace.h |   22 ++++++++++++++++++++--
 1 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index 308bafd..59e09f9 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -400,6 +400,20 @@ static inline int ftrace_get_offsets_##call(				\
  *
  */
 
+#ifdef MODULE
+# define event_trace_up_ref()					\
+	do {							\
+		if (!try_module_get(THIS_MODULE)) {		\
+			atomic_dec(&event_call->profile_count);	\
+			return -ENOENT;				\
+		}						\
+	} while (0)
+# define event_trace_down_ref() module_put(THIS_MODULE)
+#else
+# define event_trace_up_ref() do { } while (0)
+# define event_trace_down_ref() do { } while (0)
+#endif
+
 #undef TRACE_EVENT
 #define TRACE_EVENT(call, proto, args, tstruct, assign, print)		\
 									\
@@ -409,16 +423,20 @@ static int ftrace_profile_enable_##call(struct ftrace_event_call *event_call) \
 {									\
 	int ret = 0;							\
 									\
-	if (!atomic_inc_return(&event_call->profile_count))		\
+	if (!atomic_inc_return(&event_call->profile_count)) {		\
+		event_trace_up_ref();					\
 		ret = register_trace_##call(ftrace_profile_##call);	\
+	}								\
 									\
 	return ret;							\
 }									\
 									\
 static void ftrace_profile_disable_##call(struct ftrace_event_call *event_call)\
 {									\
-	if (atomic_add_negative(-1, &event_call->profile_count))	\
+	if (atomic_add_negative(-1, &event_call->profile_count)) {	\
 		unregister_trace_##call(ftrace_profile_##call);		\
+		event_trace_down_ref();					\
+	}								\
 }
 
 #include TRACE_INCLUDE(TRACE_INCLUDE_FILE)
-- 
1.6.3.3

--