tracing/kprobe: Wait for disabling all running kprobe handlers

commit a232e270 upstream.

Wait for disabling all running kprobe handlers when a kprobe
event is disabled, since the caller, trace_remove_event_call()
supposes that a removing event is disabled completely by
disabling the event.
With this change, ftrace can ensure that there is no running
event handlers after disabling it.

Link: http://lkml.kernel.org/r/20130709093526.20138.93100.stgit@mhiramat-M0-7522Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

kernel/trace/trace_kprobe.c

@@ -281,6 +281,8 @@ trace_probe_file_index(struct trace_probe *tp, struct ftrace_event_file *file)
 static int
 disable_trace_probe(struct trace_probe *tp, struct ftrace_event_file *file)
 {
+	struct ftrace_event_file **old = NULL;
+	int wait = 0;
 	int ret = 0;
 
 	mutex_lock(&probe_enable_lock);
@@ -314,10 +316,7 @@ disable_trace_probe(struct trace_probe *tp, struct ftrace_event_file *file)
 		}
 
 		rcu_assign_pointer(tp->files, new);
-
-		/* Make sure the probe is done with old files */
-		synchronize_sched();
-		kfree(old);
+		wait = 1;
 	} else
 		tp->flags &= ~TP_FLAG_PROFILE;
 
@@ -326,11 +325,25 @@ disable_trace_probe(struct trace_probe *tp, struct ftrace_event_file *file)
 			disable_kretprobe(&tp->rp);
 		else
 			disable_kprobe(&tp->rp.kp);
+		wait = 1;
 	}
 
  out_unlock:
 	mutex_unlock(&probe_enable_lock);
 
+	if (wait) {
+		/*
+		 * Synchronize with kprobe_trace_func/kretprobe_trace_func
+		 * to ensure disabled (all running handlers are finished).
+		 * This is not only for kfree(), but also the caller,
+		 * trace_remove_event_call() supposes it for releasing
+		 * event_call related objects, which will be accessed in
+		 * the kprobe_trace_func/kretprobe_trace_func.
+		 */
+		synchronize_sched();
+		kfree(old);	/* Ignored if link == NULL */
+	}
+
 	return ret;
 }