tracing: Protect tracer flags with trace_types_lock

commit 69d34da2 upstream.

Seems that the tracer flags have never been protected from
synchronous writes. Luckily, admins don't usually modify the
tracing flags via two different tasks. But if scripts were to
be used to modify them, then they could get corrupted.

Move the trace_types_lock that protects against tracers changing
to also protect the flags being set.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
[bwh: Backported to 3.2: also move failure return in
 tracing_trace_options_write() after unlocking]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

kernel/trace/trace.c

@@ -2661,7 +2661,7 @@ tracing_trace_options_write(struct file *filp, const char __user *ubuf,
 	char buf[64];
 	char *cmp;
 	int neg = 0;
-	int ret;
+	int ret = 0;
 	int i;
 
 	if (cnt >= sizeof(buf))
@@ -2678,6 +2678,8 @@ tracing_trace_options_write(struct file *filp, const char __user *ubuf,
 		cmp += 2;
 	}
 
+	mutex_lock(&trace_types_lock);
+
 	for (i = 0; trace_options[i]; i++) {
 		if (strcmp(cmp, trace_options[i]) == 0) {
 			set_tracer_flags(1 << i, !neg);
@@ -2686,13 +2688,13 @@ tracing_trace_options_write(struct file *filp, const char __user *ubuf,
 	}
 
 	/* If no option could be set, test the specific tracer options */
-	if (!trace_options[i]) {
-		mutex_lock(&trace_types_lock);
+	if (!trace_options[i])
 		ret = set_tracer_option(current_trace, cmp, neg);
-		mutex_unlock(&trace_types_lock);
-		if (ret)
-			return ret;
-	}
+
+	mutex_unlock(&trace_types_lock);
+
+	if (ret)
+		return ret;
 
 	*ppos += cnt;
 
@@ -4379,7 +4381,10 @@ trace_options_core_write(struct file *filp, const char __user *ubuf, size_t cnt,
 
 	if (val != 0 && val != 1)
 		return -EINVAL;
+
+	mutex_lock(&trace_types_lock);
 	set_tracer_flags(1 << index, val);
+	mutex_unlock(&trace_types_lock);
 
 	*ppos += cnt;