--- linux-2.6.16.13-xen/drivers/xen/netback/netback.c	2006-06-04 01:03:54.000000000 -0400
+++ new/drivers/xen/netback/netback.c	2006-06-04 23:05:21.000000000 -0400
@@ -100,6 +100,7 @@
 static unsigned long mfn_list[MAX_MFN_ALLOC];
 static unsigned int alloc_index = 0;
 static DEFINE_SPINLOCK(mfn_lock);
+static DEFINE_SPINLOCK(_lock);
 
 static unsigned long alloc_mfn(void)
 {
@@ -454,9 +455,19 @@
 	PEND_RING_IDX dc, dp;
 	netif_t *netif;
 	int ret;
+	unsigned long flags;
 
 	dc = dealloc_cons;
+
+	/*
+	 * dealloc_prod is updated under the protection of the spin lock
+	 * in the function netif_idx_release(). We need to see the updates to
+	 * dealloc_prod in the order it is updated in netif_idx_release. To 
+	 * force this, snapshot dealloc_prod under the protection of the lock.
+	 */
+	spin_lock_irqsave(&_lock, flags);
 	dp = dealloc_prod;
+	spin_unlock_irqrestore(&_lock, flags);
 
 	/*
 	 * Free up any grants we have finished using
@@ -691,7 +702,6 @@
 
 static void netif_idx_release(u16 pending_idx)
 {
-	static DEFINE_SPINLOCK(_lock);
 	unsigned long flags;
 
 	spin_lock_irqsave(&_lock, flags);