patches/printk-rt-aware.patch

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

Drop the lock before calling the console driver and do not disable
interrupts while printing to a serial console.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 kernel/printk/printk.c |   27 +++++++++++++++++++++++----
 1 file changed, 23 insertions(+), 4 deletions(-)

--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1502,6 +1502,7 @@ static void call_console_drivers(int lev
 	if (!console_drivers)
 		return;
 
+	migrate_disable();
 	for_each_console(con) {
 		if (exclusive_console && con != exclusive_console)
 			continue;
@@ -1517,6 +1518,7 @@ static void call_console_drivers(int lev
 		else
 			con->write(con, text, len);
 	}
+	migrate_enable();
 }
 
 /*
@@ -1577,6 +1579,15 @@ static inline int can_use_console(unsign
 static int console_trylock_for_printk(void)
 {
 	unsigned int cpu = smp_processor_id();
+#ifdef CONFIG_PREEMPT_RT_FULL
+	int lock = !early_boot_irqs_disabled && (preempt_count() == 0) &&
+		!irqs_disabled();
+#else
+	int lock = 1;
+#endif
+
+	if (!lock)
+		return 0;
 
 	if (!console_trylock())
 		return 0;
@@ -1879,8 +1890,7 @@ asmlinkage int vprintk_emit(int facility
 		 * console_sem which would prevent anyone from printing to
 		 * console
 		 */
-		preempt_disable();
-
+		migrate_disable();
 		/*
 		 * Try to acquire and then immediately release the console
 		 * semaphore.  The release will print out buffers and wake up
@@ -1888,7 +1898,7 @@ asmlinkage int vprintk_emit(int facility
 		 */
 		if (console_trylock_for_printk())
 			console_unlock();
-		preempt_enable();
+		migrate_enable();
 		lockdep_on();
 	}
 
@@ -2248,11 +2258,16 @@ static void console_cont_flush(char *tex
 		goto out;
 
 	len = cont_print_text(text, size);
+#ifdef CONFIG_PREEMPT_RT_FULL
+	raw_spin_unlock_irqrestore(&logbuf_lock, flags);
+	call_console_drivers(cont.level, NULL, 0, text, len);
+#else
 	raw_spin_unlock(&logbuf_lock);
 	stop_critical_timings();
 	call_console_drivers(cont.level, NULL, 0, text, len);
 	start_critical_timings();
 	local_irq_restore(flags);
+#endif
 	return;
 out:
 	raw_spin_unlock_irqrestore(&logbuf_lock, flags);
@@ -2362,13 +2377,17 @@ void console_unlock(void)
 		console_idx = log_next(console_idx);
 		console_seq++;
 		console_prev = msg->flags;
+#ifdef CONFIG_PREEMPT_RT_FULL
+		raw_spin_unlock_irqrestore(&logbuf_lock, flags);
+		call_console_drivers(level, ext_text, ext_len, text, len);
+#else
 		raw_spin_unlock(&logbuf_lock);
 
 		stop_critical_timings();	/* don't trace print latency */
 		call_console_drivers(level, ext_text, ext_len, text, len);
 		start_critical_timings();
 		local_irq_restore(flags);
-
+#endif
 		if (do_cond_resched)
 			cond_resched();
 	}