tty: usb-serial krefs

Use kref in the USB serial drivers so that we don't free tty structures
from under the URB receive handlers as has historically been the case if
you were unlucky. This also gives us a framework for general tty drivers to
use tty_port objects and refcount.

Contains two err->dev_err changes merged together to fix clashes in the
-next tree.

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 11 insertions, 7 deletions

diff --git a/drivers/usb/serial/visor.c b/drivers/usb/serial/visor.c
index cf8924f9a2cc..a6d1c75a1c89 100644
--- a/drivers/usb/serial/visor.c
+++ b/drivers/usb/serial/visor.c
@@ -499,7 +499,7 @@ static void visor_read_bulk_callback(struct urb *urb)
         int status = urb->status;
         struct tty_struct *tty;
         int result;
-        int available_room;
+        int available_room = 0;
 
         dbg("%s - port %d", __func__, port->number);
 
@@ -512,13 +512,17 @@ static void visor_read_bulk_callback(struct urb *urb)
         usb_serial_debug_data(debug, &port->dev, __func__,
                                                 urb->actual_length, data);
 
-        tty = port->port.tty;
-        if (tty && urb->actual_length) {
-                available_room = tty_buffer_request_room(tty,
+        if (urb->actual_length) {
+                tty = tty_port_tty_get(&port->port);
+                if (tty) {
+                        available_room = tty_buffer_request_room(tty,
                                                         urb->actual_length);
-                if (available_room) {
-                        tty_insert_flip_string(tty, data, available_room);
-                        tty_flip_buffer_push(tty);
+                        if (available_room) {
+                                tty_insert_flip_string(tty, data,
+                                                        available_room);
+                                tty_flip_buffer_push(tty);
+                        }
+                        tty_kref_put(tty);
                 }
                 spin_lock(&priv->lock);
                 priv->bytes_in += available_room;