tracing/samples: Fix creation and deletion of simple_thread_fn creation

Commit 7496946a ("tracing: Add samples of DECLARE_EVENT_CLASS() and
DEFINE_EVENT()") added template examples for all the events. It created a
DEFINE_EVENT_FN() example which reused the foo_bar_reg and foo_bar_unreg

Enabling both the TRACE_EVENT_FN() and DEFINE_EVENT_FN() example trace
events caused the foo_bar_reg to be called twice, creating the test thread
twice. The foo_bar_unreg would remove it only once, even if it was called
multiple times, leaving a thread existing when the module is unloaded,
causing an oops.

Add a ref count and allow foo_bar_reg() and foo_bar_unreg() be called by
multiple trace events.

Fixes: 7496946a ("tracing: Add samples of DECLARE_EVENT_CLASS() and DEFINE_EVENT()")
Signed-off-by: default avatarSteven Rostedt (VMware) <>
parent f39b536c
......@@ -78,29 +78,37 @@ static int simple_thread_fn(void *arg)
static DEFINE_MUTEX(thread_mutex);
static bool simple_thread_cnt;
int foo_bar_reg(void)
if (simple_thread_cnt++)
goto out;
pr_info("Starting thread for foo_bar_fn\n");
* We shouldn't be able to start a trace when the module is
* unloading (there's other locks to prevent that). But
* for consistency sake, we still take the thread_mutex.
simple_tsk_fn = kthread_run(simple_thread_fn, NULL, "event-sample-fn");
return 0;
void foo_bar_unreg(void)
pr_info("Killing thread for foo_bar_fn\n");
/* protect against module unloading */
if (--simple_thread_cnt)
goto out;
pr_info("Killing thread for foo_bar_fn\n");
if (simple_tsk_fn)
simple_tsk_fn = NULL;
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