[PATCH v2 1/3] virtio_console: Fix locking of vtermno.

[Miche Baker-Harvey]

Some modifications of vtermno were not done under the spinlock.

Moved assignment from vtermno and increment of vtermno together,
putting both under the spinlock.  Revert vtermno on failure.

Signed-off-by: Miche Baker-Harvey <miche at google.com>
---
 drivers/char/virtio_console.c |    9 ++++++---
 1 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 8e3c46d..9722e76 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -987,18 +987,21 @@ int init_port_console(struct port *port)
 	 * pointers.  The final argument is the output buffer size: we
 	 * can do any size, so we put PAGE_SIZE here.
 	 */
-	port->cons.vtermno = pdrvdata.next_vtermno;
+	spin_lock_irq(&pdrvdata_lock);
+	port->cons.vtermno = pdrvdata.next_vtermno++;
+	spin_unlock_irq(&pdrvdata_lock);
 
 	port->cons.hvc = hvc_alloc(port->cons.vtermno, 0, &hv_ops, PAGE_SIZE);
+	spin_lock_irq(&pdrvdata_lock);
 	if (IS_ERR(port->cons.hvc)) {
 		ret = PTR_ERR(port->cons.hvc);
 		dev_err(port->dev,
 			"error %d allocating hvc for port\n", ret);
 		port->cons.hvc = NULL;
+		port->cons.vtermno = pdrvdata.next_vtermno--;
+		spin_unlock_irq(&pdrvdata_lock);
 		return ret;
 	}
-	spin_lock_irq(&pdrvdata_lock);
-	pdrvdata.next_vtermno++;
 	list_add_tail(&port->cons.list, &pdrvdata.consoles);
 	spin_unlock_irq(&pdrvdata_lock);
 	port->guest_connected = true;