rt-serial-warn-fix.patch

Subject: rt: Improve the serial console PASS_LIMIT
From: Ingo Molnar <mingo@elte.hu>
Date: Wed Dec 14 13:05:54 CET 2011

Beyond the warning:

 drivers/tty/serial/8250/8250.c:1613:6: warning: unused variable ‘pass_counter’ [-Wunused-variable]

the solution of just looping infinitely was ugly - up it to 1 million to
give it a chance to continue in some really ugly situation.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 drivers/tty/serial/8250/8250.c |   13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

Index: linux-stable/drivers/tty/serial/8250/8250.c
===================================================================
--- linux-stable.orig/drivers/tty/serial/8250/8250.c
+++ linux-stable/drivers/tty/serial/8250/8250.c
@@ -80,7 +80,16 @@ static unsigned int skip_txen_test; /* f
 #define DEBUG_INTR(fmt...)	do { } while (0)
 #endif
 
-#define PASS_LIMIT	512
+/*
+ * On -rt we can have a more delays, and legitimately
+ * so - so don't drop work spuriously and spam the
+ * syslog:
+ */
+#ifdef CONFIG_PREEMPT_RT_FULL
+# define PASS_LIMIT	1000000
+#else
+# define PASS_LIMIT	512
+#endif
 
 #define BOTH_EMPTY 	(UART_LSR_TEMT | UART_LSR_THRE)
 
@@ -1549,14 +1558,12 @@ static irqreturn_t serial8250_interrupt(
 
 		l = l->next;
 
-#ifndef CONFIG_PREEMPT_RT_FULL
 		if (l == i->head && pass_counter++ > PASS_LIMIT) {
 			/* If we hit this, we're dead. */
 			printk_ratelimited(KERN_ERR
 				"serial8250: too much work for irq%d\n", irq);
 			break;
 		}
-#endif
 	} while (l != end);
 
 	spin_unlock(&i->lock);