1 files changed, 17 insertions, 1 deletions
diff --git a/sys/kern/printf.c b/sys/kern/printf.c
index dfd0657..89add9e 100644
--- a/sys/kern/printf.c
+++ b/sys/kern/printf.c
@@ -1,10 +1,14 @@
 #include <printf.h>
 #include <stdint.h>
+#include <spinlock.h>
 #include <sbi.h>
 #include <stdarg.h>
 
 static char digits[] = "0123456789abcdef";
 
+struct spinlock mutex;
+int locked = 0;
+
 int
 puts(const char *str)
 {
@@ -52,9 +56,13 @@ void
 printf(const char *fmt, ...) 
 {
         va_list ap;
-        int i, c;
+        int i, c, _locked;
         char *s;
 
+	_locked = locked;
+	if (_locked)
+		acquire(&mutex);
+
         va_start(ap, fmt);
 
         for (i = 0; (c = fmt[i] & 0xff) != 0; i++) {
@@ -82,4 +90,12 @@ printf(const char *fmt, ...)
                                 break;
                 }
         }
+	if (_locked)
+		release(&mutex);
+}
+
+void printf_init(void)
+{
+	initlock(&mutex);
+	locked = 1;
 }