Subject: printk-kill.patch
From: Ingo Molnar <mingo@elte.hu>
Date: Fri, 22 Jul 2011 17:58:40 +0200

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 include/linux/printk.h |    3 ++-
 kernel/printk.c        |   33 +++++++++++++++++++++++++++++++++
 kernel/watchdog.c      |   15 +++++++++++++--
 3 files changed, 48 insertions(+), 3 deletions(-)

Index: linux-stable/include/linux/printk.h
===================================================================
--- linux-stable.orig/include/linux/printk.h
+++ linux-stable/include/linux/printk.h
@@ -99,9 +99,11 @@ int no_printk(const char *fmt, ...)
 extern asmlinkage __printf(1, 2)
 void early_printk(const char *fmt, ...);
 void early_vprintk(const char *fmt, va_list ap);
+extern void printk_kill(void);
 #else
 static inline __printf(1, 2) __cold
 void early_printk(const char *s, ...) { }
+static inline void printk_kill(void) { }
 #endif
 
 extern int printk_needs_cpu(int cpu);
@@ -138,7 +140,6 @@ extern int __printk_ratelimit(const char
 #define printk_ratelimit() __printk_ratelimit(__func__)
 extern bool printk_timed_ratelimit(unsigned long *caller_jiffies,
 				   unsigned int interval_msec);
-
 extern int printk_delay_msec;
 extern int dmesg_restrict;
 extern int kptr_restrict;
Index: linux-stable/kernel/printk.c
===================================================================
--- linux-stable.orig/kernel/printk.c
+++ linux-stable/kernel/printk.c
@@ -1246,6 +1246,32 @@ asmlinkage void early_printk(const char 
 	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
 
 static bool __read_mostly ignore_loglevel;
@@ -1508,6 +1534,13 @@ asmlinkage int vprintk_emit(int facility
 	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();
 	printk_delay();
 
Index: linux-stable/kernel/watchdog.c
===================================================================
--- linux-stable.orig/kernel/watchdog.c
+++ linux-stable/kernel/watchdog.c
@@ -202,6 +202,8 @@ static int is_softlockup(unsigned long t
 
 #ifdef CONFIG_HARDLOCKUP_DETECTOR
 
+static DEFINE_RAW_SPINLOCK(watchdog_output_lock);
+
 static struct perf_event_attr wd_hw_attr = {
 	.type		= PERF_TYPE_HARDWARE,
 	.config		= PERF_COUNT_HW_CPU_CYCLES,
@@ -236,10 +238,19 @@ static void watchdog_overflow_callback(s
 		if (__this_cpu_read(hard_watchdog_warn) == true)
 			return;
 
-		if (hardlockup_panic)
+		/*
+		 * If early-printk is enabled then make sure we do not
+		 * lock up in printk() and kill console logging:
+		 */
+		printk_kill();
+
+		if (hardlockup_panic) {
 			panic("Watchdog detected hard LOCKUP on cpu %d", this_cpu);
-		else
+		} else {
+			raw_spin_lock(&watchdog_output_lock);
 			WARN(1, "Watchdog detected hard LOCKUP on cpu %d", this_cpu);
+			raw_spin_unlock(&watchdog_output_lock);
+		}
 
 		__this_cpu_write(hard_watchdog_warn, true);
 		return;