From 8d627274e496041f381a09ef1c0fa166ae3693d9 Mon Sep 17 00:00:00 2001
From: Jason Wessel <jason.wessel@windriver.com>
Date: Thu, 28 Jul 2011 12:42:23 -0500
Subject: kgdb/serial: Short term workaround

On 07/27/2011 04:37 PM, Thomas Gleixner wrote:
>  - KGDB (not yet disabled) is reportedly unusable on -rt right now due
>    to missing hacks in the console locking which I dropped on purpose.
>

To work around this in the short term you can use this patch, in
addition to the clocksource watchdog patch that Thomas brewed up.

Comments are welcome of course.  Ultimately the right solution is to
change separation between the console and the HW to have a polled mode
+ work queue so as not to introduce any kind of latency.

Thanks,
Jason.

diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
index 0ed004d..969e264 100644
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -38,6 +38,7 @@
 #include <linux/nmi.h>
 #include <linux/mutex.h>
 #include <linux/slab.h>
+#include <linux/kdb.h>
 #ifdef CONFIG_SPARC
 #include <linux/sunserialcore.h>
 #endif
@@ -2873,7 +2874,7 @@ serial8250_console_write(struct console *co, const char *s, unsigned int count)
 
 	touch_nmi_watchdog();
 
-	if (port->sysrq || oops_in_progress)
+	if (port->sysrq || oops_in_progress || in_kdb_printk())
 		locked = spin_trylock_irqsave(&port->lock, flags);
 	else
 		spin_lock_irqsave(&port->lock, flags);
diff --git a/include/linux/kdb.h b/include/linux/kdb.h
index 7f6fe6e..680ad23 100644
--- a/include/linux/kdb.h
+++ b/include/linux/kdb.h
@@ -115,7 +115,7 @@ extern int kdb_trap_printk;
 extern __printf(1, 0) int vkdb_printf(const char *fmt, va_list args);
 extern __printf(1, 2) int kdb_printf(const char *, ...);
 typedef __printf(1, 2) int (*kdb_printf_t)(const char *, ...);
-
+#define in_kdb_printk() (kdb_trap_printk)
 extern void kdb_init(int level);
 
 /* Access to kdb specific polling devices */
@@ -150,6 +150,7 @@ extern int kdb_register_repeat(char *, kdb_func_t, char *, char *,
 extern int kdb_unregister(char *);
 #else /* ! CONFIG_KGDB_KDB */
 static inline __printf(1, 2) int kdb_printf(const char *fmt, ...) { return 0; }
+#define in_kdb_printk() (0)
 static inline void kdb_init(int level) {}
 static inline int kdb_register(char *cmd, kdb_func_t func, char *usage,
 			       char *help, short minlen) { return 0; }
diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
index 14ff484..399dba6 100644
--- a/kernel/debug/kdb/kdb_io.c
+++ b/kernel/debug/kdb/kdb_io.c
@@ -554,7 +554,6 @@ int vkdb_printf(const char *fmt, va_list ap)
 	int linecount;
 	int colcount;
 	int logging, saved_loglevel = 0;
-	int saved_trap_printk;
 	int got_printf_lock = 0;
 	int retlen = 0;
 	int fnd, len;
@@ -565,8 +564,6 @@ int vkdb_printf(const char *fmt, va_list ap)
 	unsigned long uninitialized_var(flags);
 
 	preempt_disable();
-	saved_trap_printk = kdb_trap_printk;
-	kdb_trap_printk = 0;
 
 	/* Serialize kdb_printf if multiple cpus try to write at once.
 	 * But if any cpu goes recursive in kdb, just print the output,
@@ -833,7 +830,6 @@ kdb_print_out:
 	} else {
 		__release(kdb_printf_lock);
 	}
-	kdb_trap_printk = saved_trap_printk;
 	preempt_enable();
 	return retlen;
 }
@@ -843,9 +839,11 @@ int kdb_printf(const char *fmt, ...)
 	va_list ap;
 	int r;
 
+	kdb_trap_printk++;
 	va_start(ap, fmt);
 	r = vkdb_printf(fmt, ap);
 	va_end(ap);
+	kdb_trap_printk--;
 
 	return r;
 }
-- 
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