xenfb: connect to backend before registering fb

As soon as the framebuffer is registered, our methods may be called by the
kernel. This leads to a crash as xenfb_refresh() gets called before we have
the irq.

Connect to the backend before registering our framebuffer with the kernel.

[ Fixes bug http://bugzilla.kernel.org/show_bug.cgi?id=14059 ]
Signed-off-by: Michal Schmidt <mschmidt@redhat.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/video/xen-fbfront.c

@@ -454,6 +454,10 @@ static int __devinit xenfb_probe(struct xenbus_device *dev,
 
 	xenfb_init_shared_page(info, fb_info);
 
+	ret = xenfb_connect_backend(dev, info);
+	if (ret < 0)
+		goto error;
+
 	ret = register_framebuffer(fb_info);
 	if (ret) {
 		fb_deferred_io_cleanup(fb_info);
@@ -464,10 +468,6 @@ static int __devinit xenfb_probe(struct xenbus_device *dev,
 	}
 	info->fb_info = fb_info;
 
-	ret = xenfb_connect_backend(dev, info);
-	if (ret < 0)
-		goto error;
-
 	xenfb_make_preferred_console();
 	return 0;