Subject: printk-rt-aware.patch
From: Thomas Gleixner <tglx@linutronix.de>
Date: Wed, 19 Sep 2012 14:50:37 +0200

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 kernel/printk.c |   33 +++++++++++++++++++++++++++++----
 1 file changed, 29 insertions(+), 4 deletions(-)

Index: linux-stable/kernel/printk.c
===================================================================
--- linux-stable.orig/kernel/printk.c
+++ linux-stable/kernel/printk.c
@@ -1312,6 +1312,7 @@ static void call_console_drivers(int lev
 	if (!console_drivers)
 		return;
 
+	migrate_disable();
 	for_each_console(con) {
 		if (exclusive_console && con != exclusive_console)
 			continue;
@@ -1324,6 +1325,7 @@ static void call_console_drivers(int lev
 			continue;
 		con->write(con, text, len);
 	}
+	migrate_enable();
 }
 
 /*
@@ -1383,12 +1385,18 @@ static inline int can_use_console(unsign
  * interrupts disabled. It should return with 'lockbuf_lock'
  * released but interrupts still disabled.
  */
-static int console_trylock_for_printk(unsigned int cpu)
+static int console_trylock_for_printk(unsigned int cpu, unsigned long flags)
 	__releases(&logbuf_lock)
 {
 	int retval = 0, wake = 0;
+#ifdef CONFIG_PREEMPT_RT_FULL
+	int lock = !early_boot_irqs_disabled && !irqs_disabled_flags(flags) &&
+		(preempt_count() <= 1);
+#else
+	int lock = 1;
+#endif
 
-	if (console_trylock()) {
+	if (lock && console_trylock()) {
 		retval = 1;
 
 		/*
@@ -1667,8 +1675,15 @@ asmlinkage int vprintk_emit(int facility
 	 * The console_trylock_for_printk() function will release 'logbuf_lock'
 	 * regardless of whether it actually gets the console semaphore or not.
 	 */
-	if (console_trylock_for_printk(this_cpu))
+	if (console_trylock_for_printk(this_cpu, flags)) {
+#ifndef CONFIG_PREEMPT_RT_FULL
+		console_unlock();
+#else
+		raw_local_irq_restore(flags);
 		console_unlock();
+		raw_local_irq_save(flags);
+#endif
+	}
 
 	lockdep_on();
 out_restore_irqs:
@@ -2057,11 +2072,16 @@ static void console_cont_flush(char *tex
 		goto out;
 
 	len = cont_print_text(text, size);
+#ifndef CONFIG_PREEMPT_RT_FULL
 	raw_spin_unlock(&logbuf_lock);
 	stop_critical_timings();
 	call_console_drivers(cont.level, text, len);
 	start_critical_timings();
 	local_irq_restore(flags);
+#else
+	raw_spin_unlock_irqrestore(&logbuf_lock, flags);
+	call_console_drivers(cont.level, text, len);
+#endif
 	return;
 out:
 	raw_spin_unlock_irqrestore(&logbuf_lock, flags);
@@ -2144,12 +2164,17 @@ skip:
 		console_idx = log_next(console_idx);
 		console_seq++;
 		console_prev = msg->flags;
-		raw_spin_unlock(&logbuf_lock);
 
+#ifndef CONFIG_PREEMPT_RT_FULL
+		raw_spin_unlock(&logbuf_lock);
 		stop_critical_timings();	/* don't trace print latency */
 		call_console_drivers(level, text, len);
 		start_critical_timings();
 		local_irq_restore(flags);
+#else
+		raw_spin_unlock_irqrestore(&logbuf_lock, flags);
+		call_console_drivers(level, text, len);
+#endif
 	}
 	console_locked = 0;