linux-kernel - Re: PATCH? trace_remove_event_call() should fail if call is active

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Date:	Wed, 3 Jul 2013 00:23:59 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	"zhangwei(Jovi)" <jovi.zhangwei@...wei.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: PATCH? trace_remove_event_call() should fail if call is active

On 07/02, Oleg Nesterov wrote:
>
> So please ignore modules ;)

Or lets discuss the change above.

Oleg.

--- x/kernel/trace/trace_events.c
+++ x/kernel/trace/trace_events.c
@@ -1611,14 +1611,40 @@ static void __trace_remove_event_call(st
 	destroy_preds(call);
 }
 
+static int event_can_remove(struct ftrace_event_call *call)
+{
+	struct trace_array *tr;
+	struct ftrace_event_file *file;
+
+#ifdef CONFIG_PERF_EVENTS
+	if (call->perf_refcount)
+		return -EBUSY;
+#endif
+	do_for_each_event_file(tr, file) {
+		if (file->event_call != call)
+			continue;
+		if (file->flags & FTRACE_EVENT_FL_ENABLED)
+			return -EBUSY;
+		break;
+	} while_for_each_event_file();
+
+	return 0;
+}
+
 /* Remove an event_call */
-void trace_remove_event_call(struct ftrace_event_call *call)
+int trace_remove_event_call(struct ftrace_event_call *call)
 {
+	int err;
+
 	mutex_lock(&event_mutex);
 	down_write(&trace_event_sem);
-	__trace_remove_event_call(call);
+	err = event_can_remove(call);
+	if (!err)
+		__trace_remove_event_call(call);
 	up_write(&trace_event_sem);
 	mutex_unlock(&event_mutex);
+
+	return err;
 }
 
 #define for_each_event(event, start, end)			\

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