USB: cdc-wdm: cannot use dev_printk when device is gone

commit 6b0b79d3 upstream.

We cannot dereference a removed USB interface for
dev_printk. Use pr_debug instead where necessary.

Flush errors are expected if device is unplugged and are
therefore best ingored at this point.

Move the kill_urbs() call in wdm_release with dev_dbg()
for the non disconnect, as we know it has already been
called if WDM_DISCONNECTING is set.  This does not
actually fix anything, but keeps the code more consistent.

Cc: Oliver Neukum <oliver@neukum.org>
Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/usb/class/cdc-wdm.c

@@ -496,7 +496,9 @@ static int wdm_flush(struct file *file, fl_owner_t id)
 	struct wdm_device *desc = file->private_data;
 
 	wait_event(desc->wait, !test_bit(WDM_IN_USE, &desc->flags));
-	if (desc->werr < 0)
+
+	/* cannot dereference desc->intf if WDM_DISCONNECTING */
+	if (desc->werr < 0 && !test_bit(WDM_DISCONNECTING, &desc->flags))
 		dev_err(&desc->intf->dev, "Error in flush path: %d\n",
 			desc->werr);
 
@@ -586,12 +588,13 @@ static int wdm_release(struct inode *inode, struct file *file)
 	mutex_unlock(&desc->wlock);
 
 	if (!desc->count) {
-		dev_dbg(&desc->intf->dev, "wdm_release: cleanup");
-		kill_urbs(desc);
 		if (!test_bit(WDM_DISCONNECTING, &desc->flags)) {
+			dev_dbg(&desc->intf->dev, "wdm_release: cleanup");
+			kill_urbs(desc);
 			desc->intf->needs_remote_wakeup = 0;
 		} else {
-			dev_dbg(&desc->intf->dev, "%s: device gone - cleaning up\n", __func__);
+			/* must avoid dev_printk here as desc->intf is invalid */
+			pr_debug(KBUILD_MODNAME " %s: device gone - cleaning up\n", __func__);
 			cleanup(desc);
 		}
 	}