diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index db7a02e05241a1c89a066922cb06b0b2a4bef457..012f3e40671dcb83865ed08d78146902cc8f9fd8 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1561,6 +1561,11 @@ asmlinkage int vprintk_emit(int facility, int level,
 			case 'd':	/* KERN_DEFAULT */
 				lflags |= LOG_PREFIX;
 			}
+			/*
+			 * No need to check length here because vscnprintf
+			 * put '\0' at the end of the string. Only valid and
+			 * newly printed level is detected.
+			 */
 			text_len -= end_of_header - text;
 			text = (char *)end_of_header;
 		}