diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index eac2824..18b86c3 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4408,13 +4408,15 @@ static int trace_set_options(struct trace_array *tr, char *option)
 	int neg = 0;
 	int ret;
 	size_t orig_len = strlen(option);
+	int len;
 
 	cmp = strstrip(option);
 
-	if (str_has_prefix(cmp, "no")) {
+	len = str_has_prefix(cmp, "no");
+	if (len)
 		neg = 1;
-		cmp += 2;
-	}
+
+	cmp += len;
 
 	mutex_lock(&trace_types_lock);
 
diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index 5413757..9962cb5 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -186,19 +186,20 @@ int traceprobe_parse_event_name(const char **pevent, const char **pgroup,
 static int parse_probe_vars(char *arg, const struct fetch_type *t,
 			    struct fetch_insn *code, unsigned int flags)
 {
-	int ret = 0;
 	unsigned long param;
+	int ret = 0;
+	int len;
 
 	if (strcmp(arg, "retval") == 0) {
 		if (flags & TPARG_FL_RETURN)
 			code->op = FETCH_OP_RETVAL;
 		else
 			ret = -EINVAL;
-	} else if (str_has_prefix(arg, "stack")) {
-		if (arg[5] == '\0') {
+	} else if ((len = str_has_prefix(arg, "stack"))) {
+		if (arg[len] == '\0') {
 			code->op = FETCH_OP_STACKP;
-		} else if (isdigit(arg[5])) {
-			ret = kstrtoul(arg + 5, 10, &param);
+		} else if (isdigit(arg[len])) {
+			ret = kstrtoul(arg + len, 10, &param);
 			if (ret || ((flags & TPARG_FL_KERNEL) &&
 				    param > PARAM_MAX_STACK))
 				ret = -EINVAL;
@@ -213,10 +214,10 @@ static int parse_probe_vars(char *arg, const struct fetch_type *t,
 #ifdef CONFIG_HAVE_FUNCTION_ARG_ACCESS_API
 	} else if (((flags & TPARG_FL_MASK) ==
 		    (TPARG_FL_KERNEL | TPARG_FL_FENTRY)) &&
-		   str_has_prefix(arg, "arg")) {
-		if (!isdigit(arg[3]))
+		   (len = str_has_prefix(arg, "arg"))) {
+		if (!isdigit(arg[len]))
 			return -EINVAL;
-		ret = kstrtoul(arg + 3, 10, &param);
+		ret = kstrtoul(arg + len, 10, &param);
 		if (ret || !param || param > PARAM_MAX_STACK)
 			return -EINVAL;
 		code->op = FETCH_OP_ARG;
diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
index 3641f28..eec648a 100644
--- a/kernel/trace/trace_stack.c
+++ b/kernel/trace/trace_stack.c
@@ -448,8 +448,10 @@ static char stack_trace_filter_buf[COMMAND_LINE_SIZE+1] __initdata;
 
 static __init int enable_stacktrace(char *str)
 {
-	if (str_has_prefix(str, "_filter="))
-		strncpy(stack_trace_filter_buf, str+8, COMMAND_LINE_SIZE);
+	int len;
+
+	if ((len = str_has_prefix(str, "_filter=")))
+		strncpy(stack_trace_filter_buf, str + len, COMMAND_LINE_SIZE);
 
 	stack_tracer_enabled = 1;
 	last_stack_tracer_enabled = 1;