printk-kill.patch

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 56 insertions, 23 deletions

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 0f91490..a93a03b 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1487,6 +1487,55 @@ static size_t cont_print_text(char *text, size_t size)
 	return textlen;
 }
 
+#ifdef CONFIG_EARLY_PRINTK
+struct console *early_console;
+
+void early_vprintk(const char *fmt, va_list ap)
+{
+	if (early_console) {
+		char buf[512];
+		int n = vscnprintf(buf, sizeof(buf), fmt, ap);
+
+		early_console->write(early_console, buf, n);
+	}
+}
+
+asmlinkage void early_printk(const char *fmt, ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	early_vprintk(fmt, ap);
+	va_end(ap);
+}
+
+/*
+ * This is independent of any log levels - a global
+ * kill switch that turns off all of printk.
+ *
+ * Used by the NMI watchdog if early-printk is enabled.
+ */
+static bool __read_mostly printk_killswitch;
+
+void printk_kill(void)
+{
+	printk_killswitch = true;
+}
+
+static int forced_early_printk(const char *fmt, va_list ap)
+{
+	if (!printk_killswitch)
+		return 0;
+	early_vprintk(fmt, ap);
+	return 1;
+}
+#else
+static inline int forced_early_printk(const char *fmt, va_list ap)
+{
+	return 0;
+}
+#endif
+
 asmlinkage int vprintk_emit(int facility, int level,
 			    const char *dict, size_t dictlen,
 			    const char *fmt, va_list args)
@@ -1500,6 +1549,13 @@ asmlinkage int vprintk_emit(int facility, int level,
 	int this_cpu;
 	int printed_len = 0;
 
+	/*
+	 * Fall back to early_printk if a debugging subsystem has
+	 * killed printk output
+	 */
+	if (unlikely(forced_early_printk(fmt, args)))
+		return 1;
+
 	boot_delay_msec(level);
 	printk_delay();
 
@@ -1722,29 +1778,6 @@ static size_t cont_print_text(char *text, size_t size) { return 0; }
 
 #endif /* CONFIG_PRINTK */
 
-#ifdef CONFIG_EARLY_PRINTK
-struct console *early_console;
-
-void early_vprintk(const char *fmt, va_list ap)
-{
-	if (early_console) {
-		char buf[512];
-		int n = vscnprintf(buf, sizeof(buf), fmt, ap);
-
-		early_console->write(early_console, buf, n);
-	}
-}
-
-asmlinkage void early_printk(const char *fmt, ...)
-{
-	va_list ap;
-
-	va_start(ap, fmt);
-	early_vprintk(fmt, ap);
-	va_end(ap);
-}
-#endif
-
 static int __add_preferred_console(char *name, int idx, char *options,
 				   char *brl_options)
 {