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Commit 6575257c authored by Steven Rostedt (VMware)'s avatar Steven Rostedt (VMware)
Browse files

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
functions.

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.

Cc: stable@vger.kernel.org
Fixes: 7496946a ("tracing: Add samples of DECLARE_EVENT_CLASS() and DEFINE_EVENT()")
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent f39b536c

samples/trace_events/trace-events-sample.c

+11 −3
Original line number Diff line number Diff line
@@ -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)

{

	mutex_lock(&thread_mutex);

	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.

	 */

	mutex_lock(&thread_mutex);

	simple_tsk_fn = kthread_run(simple_thread_fn, NULL, "event-sample-fn");

 out:

	mutex_unlock(&thread_mutex);

	return 0;

}



void foo_bar_unreg(void)

{

	pr_info("Killing thread for foo_bar_fn\n");

	/* protect against module unloading */

	mutex_lock(&thread_mutex);

	if (--simple_thread_cnt)

		goto out;



	pr_info("Killing thread for foo_bar_fn\n");

	if (simple_tsk_fn)

		kthread_stop(simple_tsk_fn);

	simple_tsk_fn = NULL;

 out:

	mutex_unlock(&thread_mutex);

}