Below is the fix. The only conflict between 4.9 and Linus's tree was
that foo_bar_reg() changed from a void to returning int.
Also, I folded in Linus's fix of having simple_thread_cnt be int and
not bool. You can remove that if you want to add Linus's commit on top.
I'm guessing this should also work for 4.4 as well?
-- Steve
------------------ original commit in Linus's tree ------------------
>From 6575257c60e1a26a5319ccf2b5ce5b6449001017 Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>
Date: Tue, 17 Oct 2017 14:55:24 -0400
Subject: [PATCH] tracing/samples: Fix creation and deletion of
simple_thread_fn creation
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.
Cc: stable@xxxxxxxxxxxxxxx
Fixes: 7496946a8 ("tracing: Add samples of DECLARE_EVENT_CLASS() and DEFINE_EVENT()")
Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Index: linux-trace.git/samples/trace_events/trace-events-sample.c
===================================================================
--- linux-trace.git.orig/samples/trace_events/trace-events-sample.c
+++ linux-trace.git/samples/trace_events/trace-events-sample.c
@@ -78,28 +78,36 @@ static int simple_thread_fn(void *arg)
}
static DEFINE_MUTEX(thread_mutex);
+static int 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);
}