tracepoints: Prevent null probe from being added

Somehow tracepoint_entry_add_probe() function allows a null probe function.
And, this may lead to unexpected results since the number of probe
functions in an entry can be counted by checking whether a probe is null
or not in the for-loop.
This patch prevents a null probe from being added.
In tracepoint_entry_remove_probe() function, checking probe parameter
within the for-loop is moved out for code efficiency, leaving the null probe
feature which removes all probe functions in the entry.

Link: http://lkml.kernel.org/r/1365991995-19445-1-git-send-email-kpark3469@gmail.com

Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Sahara <keun-o.park@windriver.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/tracepoint.c

@@ -112,7 +112,8 @@ tracepoint_entry_add_probe(struct tracepoint_entry *entry,
 	int nr_probes = 0;
 	struct tracepoint_func *old, *new;
 
-	WARN_ON(!probe);
+	if (WARN_ON(!probe))
+		return ERR_PTR(-EINVAL);
 
 	debug_print_probes(entry);
 	old = entry->funcs;
@@ -152,13 +153,18 @@ tracepoint_entry_remove_probe(struct tracepoint_entry *entry,
 
 	debug_print_probes(entry);
 	/* (N -> M), (N > 1, M >= 0) probes */
-	for (nr_probes = 0; old[nr_probes].func; nr_probes++) {
-		if (!probe ||
-		    (old[nr_probes].func == probe &&
-		     old[nr_probes].data == data))
-			nr_del++;
+	if (probe) {
+		for (nr_probes = 0; old[nr_probes].func; nr_probes++) {
+			if (old[nr_probes].func == probe &&
+			     old[nr_probes].data == data)
+				nr_del++;
+		}
 	}
 
+	/*
+	 * If probe is NULL, then nr_probes = nr_del = 0, and then the
+	 * entire entry will be removed.
+	 */
 	if (nr_probes - nr_del == 0) {
 		/* N -> 0, (N > 1) */
 		entry->funcs = NULL;
@@ -173,8 +179,7 @@ tracepoint_entry_remove_probe(struct tracepoint_entry *entry,
 		if (new == NULL)
 			return ERR_PTR(-ENOMEM);
 		for (i = 0; old[i].func; i++)
-			if (probe &&
-			    (old[i].func != probe || old[i].data != data))
+			if (old[i].func != probe || old[i].data != data)
 				new[j++] = old[i];
 		new[nr_probes - nr_del].func = NULL;
 		entry->refcount = nr_probes - nr_del;