[PATCH] hvc_console: Don't access hvc_task if not initialised

[Amit Shah]

hvc_open() can be called without having any backing device.  This
results in a call to hvc_kick() which calls wake_up_process on a NULL
pointer.  Ensure hvc is initialised by checking for a non-NULL hvc_task
before waking up the hvc thread.

This was found by an autotest run for virtio_console without having a
console backend.

CC: stable at kernel.org
Signed-off-by: Amit Shah <amit.shah at redhat.com>
---
 drivers/tty/hvc/hvc_console.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c
index e9cba13..b2cb5cc 100644
--- a/drivers/tty/hvc/hvc_console.c
+++ b/drivers/tty/hvc/hvc_console.c
@@ -286,6 +286,9 @@ EXPORT_SYMBOL_GPL(hvc_instantiate);
 /* Wake the sleeping khvcd */
 void hvc_kick(void)
 {
+	if (!hvc_task)
+		return;
+
 	hvc_kicked = 1;
 	wake_up_process(hvc_task);
 }
-- 
1.7.4