[PATCH]smp race in ipw driver

Hi,

another one in my traversal through the serial drivers.

This here is beautiful in a haiku sort of way.
You must read the urb's status before you declare it non busy or
you may read the next urb's status, not your own, and you must guard
against write reordering.

	Regards
		Oliver
Signed-off-by: Oliver Neukum <[email protected]> 
-- 
--- a/drivers/usb/serial/ipw.c	2007-03-29 13:50:52.000000000 +0200
+++ b/drivers/usb/serial/ipw.c	2007-03-29 13:53:46.000000000 +0200
@@ -369,13 +369,16 @@
 static void ipw_write_bulk_callback(struct urb *urb)
 {
 	struct usb_serial_port *port = urb->context;
+	int status;
 
 	dbg("%s", __FUNCTION__);
 
+	status = urb->status;
+	smp_mb(); /* status must be read before urb is declared unbusy */
 	port->write_urb_busy = 0;
 
-	if (urb->status)
-		dbg("%s - nonzero write bulk status received: %d", __FUNCTION__, urb->status);
+	if (status)
+		dbg("%s - nonzero write bulk status received: %d", __FUNCTION__, status);
 
 	usb_serial_port_softint(port);
 }


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