From cb950e4e5bfe1b0c18c46371b9ad9765b1270b97 Mon Sep 17 00:00:00 2001
From: Ingo Molnar <mingo@elte.hu>
Date: Fri, 22 Jul 2011 17:58:40 +0200
Subject: printk-kill.patch

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

diff --git a/include/linux/printk.h b/include/linux/printk.h
index 8111ffa..812d102 100644
--- a/include/linux/printk.h
+++ b/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 *func);
 #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;
diff --git a/kernel/printk.c b/kernel/printk.c
index 69270a6..d429e73 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -770,6 +770,32 @@ asmlinkage void early_printk(const char *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
 
 #ifdef CONFIG_BOOT_PRINTK_DELAY
@@ -1511,6 +1537,13 @@ 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();
 
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 75a2ab3..608d2fe 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -206,6 +206,8 @@ static int is_softlockup(unsigned long touch_ts)
 
 #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,
@@ -240,10 +242,19 @@ static void watchdog_overflow_callback(struct perf_event *event,
 		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;
-- 
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