printk-kill.patch

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

3 files changed, 48 insertions, 3 deletions

diff --git a/include/linux/printk.h b/include/linux/printk.h
index c8d7f7be2e5b..d5e6eed93fb7 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -91,9 +91,11 @@ int no_printk(const char *fmt, ...)
 #ifdef CONFIG_EARLY_PRINTK
 extern asmlinkage __printf(1, 2)
 void early_printk(const char *fmt, ...);
+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);
@@ -119,7 +121,6 @@ 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 c4426061e228..5a172f9e5027 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -538,6 +538,32 @@ 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
 
 static bool __read_mostly ignore_loglevel;
@@ -862,6 +888,13 @@ asmlinkage int vprintk(const char *fmt, va_list args)
 	size_t plen;
 	char special;
 
+	/*
+	 * 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();
 
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index df30ee08bdd4..de08263ff8ae 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -201,6 +201,8 @@ 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,
@@ -235,10 +237,19 @@ 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;