patches/0195-rt-Improve-the-serial-console-PASS_LIMIT.patch

From 1517773d329431d0e8371eccafbc6f3251045ce6 Mon Sep 17 00:00:00 2001
From: Ingo Molnar <mingo@elte.hu>
Date: Wed, 14 Dec 2011 13:05:54 +0100
Subject: [PATCH 195/268] rt: Improve the serial console PASS_LIMIT
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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(-)

diff --git a/drivers/tty/serial/8250/8250.c b/drivers/tty/serial/8250/8250.c
index ff93c70..a785ec0 100644
--- a/drivers/tty/serial/8250/8250.c
+++ b/drivers/tty/serial/8250/8250.c
@@ -80,7 +80,16 @@ static unsigned int skip_txen_test; /* force skip of txen test at init time */
 #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)
 
@@ -1584,14 +1593,12 @@ static irqreturn_t serial8250_interrupt(int irq, void *dev_id)
 
 		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);
-- 
1.7.10.4