[PATCH] tty: fix bug - kernel can't be pinged through when bootargs console=null

[Bryan Wu <cooloney@kernel.org>]

From: Sonic Zhang <sonic.zhang@analog.com>

when pass bootargs console=null into kernel from u-boot, the booted up
kernel can't be pinged through. This happens after the kernel is upgraded
to 2.6.28.

Should check if tty_driver is NULL before call kref_get() in tty_driver_kref_get().

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>
---
 include/linux/tty_driver.h |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/include/linux/tty_driver.h b/include/linux/tty_driver.h
index 08e0883..2a602a8 100644
--- a/include/linux/tty_driver.h
+++ b/include/linux/tty_driver.h
@@ -312,7 +312,8 @@ extern struct tty_driver *tty_find_polling_driver(char *name, int *line);
 extern void tty_driver_kref_put(struct tty_driver *driver);
 extern inline struct tty_driver *tty_driver_kref_get(struct tty_driver *d)
 {
-	kref_get(&d->kref);
+	if (d)
+		kref_get(&d->kref);
 	return d;
 }
 
-- 
1.5.6.3