Patch "tracing/samples: Fix creation and deletion of simple_thread_fn creation" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

tracing/samples: Fix creation and deletion of simple_thread_fn creation

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
tracing-samples-fix-creation-and-deletion-of-simple_thread_fn-creation.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: "Steven Rostedt (VMware)" <[email protected]>
Date: Tue, 17 Oct 2017 14:55:24 -0400
Subject: tracing/samples: Fix creation and deletion of simple_thread_fn creation

From: Steven Rostedt (VMware) <[email protected]>

commit 6575257c60e1a26a5319ccf2b5ce5b6449001017 upstream.

Commit 7496946a8 ("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.

---
 samples/trace_events/trace-events-sample.c |   14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

@@ -78,28 +78,36 @@ static int simple_thread_fn(void *arg)
 }
 
 static DEFINE_MUTEX(thread_mutex);
+static bool simple_thread_cnt;
 
 void 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);
 }
 
 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);
 }
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/tracing-samples-fix-creation-and-deletion-of-simple_thread_fn-creation.patch queue-4.4/fix-tracing-sample-code-warning.patch