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tracing/samples: Fix creation and deletion of simple_thread_fn creation

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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@vger.kernel.org
Fixes: 7496946a8 ("tracing: Add samples of DECLARE_EVENT_CLASS() and DEFINE_EVENT()")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt (VMware) 2017-10-17 14:55:24 -04:00
parent f39b536ce9
commit 6575257c60
1 changed files with 11 additions and 3 deletions
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14
samples/trace_events/trace-events-sample.c
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@ -78,29 +78,37 @@ static int simple_thread_fn(void *arg)
} }
static DEFINE_MUTEX(thread_mutex); static DEFINE_MUTEX(thread_mutex);
static bool simple_thread_cnt;
int foo_bar_reg(void) int foo_bar_reg(void)
{ {
mutex_lock(&thread_mutex);
if (simple_thread_cnt++)
goto out;
pr_info("Starting thread for foo_bar_fn\n"); pr_info("Starting thread for foo_bar_fn\n");
/* /*
* We shouldn't be able to start a trace when the module is * We shouldn't be able to start a trace when the module is
* unloading (there's other locks to prevent that). But * unloading (there's other locks to prevent that). But
* for consistency sake, we still take the thread_mutex. * 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"); simple_tsk_fn = kthread_run(simple_thread_fn, NULL, "event-sample-fn");
out:
mutex_unlock(&thread_mutex); mutex_unlock(&thread_mutex);
return 0; return 0;
} }
void foo_bar_unreg(void) void foo_bar_unreg(void)
{ {
pr_info("Killing thread for foo_bar_fn\n");
/* protect against module unloading */
mutex_lock(&thread_mutex); mutex_lock(&thread_mutex);
if (--simple_thread_cnt)
goto out;
pr_info("Killing thread for foo_bar_fn\n");
if (simple_tsk_fn) if (simple_tsk_fn)
kthread_stop(simple_tsk_fn); kthread_stop(simple_tsk_fn);
simple_tsk_fn = NULL; simple_tsk_fn = NULL;
out:
mutex_unlock(&thread_mutex); mutex_unlock(&thread_mutex);
} }