diff -r 1020c52c58c1 -r 1c4d731a68ef linux-2.6-xen-sparse/drivers/xen/pciback/pciback.h
--- a/linux-2.6-xen-sparse/drivers/xen/pciback/pciback.h	Sat Apr 22 09:41:53 2006
+++ b/linux-2.6-xen-sparse/drivers/xen/pciback/pciback.h	Tue Apr 25 16:58:33 2006
@@ -11,12 +11,17 @@
 #include <xen/xenbus.h>
 #include <linux/list.h>
 #include <linux/spinlock.h>
+#include <linux/workqueue.h>
+#include <asm/atomic.h>
 #include <xen/interface/io/pciif.h>
 
 struct pci_dev_entry {
 	struct list_head list;
 	struct pci_dev *dev;
 };
+
+#define _PDEVF_op_active 	(0)
+#define PDEVF_op_active 	(1<<(_PDEVF_op_active))
 
 struct pciback_device {
 	void *pci_dev_data;
@@ -30,6 +35,10 @@
 	int evtchn_irq;
 
 	struct xen_pci_sharedinfo *sh_info;
+
+	unsigned long flags;
+
+	struct work_struct op_work;
 };
 
 struct pciback_dev_data {
@@ -70,6 +79,7 @@
 
 /* Handles events from front-end */
 irqreturn_t pciback_handle_event(int irq, void *dev_id, struct pt_regs *regs);
+void pciback_do_op(void *data);
 
 int pciback_xenbus_register(void);
 void pciback_xenbus_unregister(void);
diff -r 1020c52c58c1 -r 1c4d731a68ef linux-2.6-xen-sparse/drivers/xen/pciback/pciback_ops.c
--- a/linux-2.6-xen-sparse/drivers/xen/pciback/pciback_ops.c	Sat Apr 22 09:41:53 2006
+++ b/linux-2.6-xen-sparse/drivers/xen/pciback/pciback_ops.c	Tue Apr 25 16:58:33 2006
@@ -40,17 +40,24 @@
 	pciback_config_reset(dev);
 }
 
-irqreturn_t pciback_handle_event(int irq, void *dev_id, struct pt_regs *regs)
+static inline void test_and_schedule_op(struct pciback_device *pdev)
 {
-	struct pciback_device *pdev = dev_id;
+	/* Check that frontend is requesting an operation and that we are not
+	 * already processing a request */
+	if (test_bit(_XEN_PCIF_active, (unsigned long *)&pdev->sh_info->flags)
+	    && !test_and_set_bit(_PDEVF_op_active, &pdev->flags))
+		schedule_work(&pdev->op_work);
+}
+
+/* Performing the configuration space reads/writes must not be done in atomic
+ * context because some of the pci_* functions can sleep (mostly due to ACPI
+ * use of semaphores). This function is intended to be called from a work
+ * queue in process context taking a struct pciback_device as a parameter */
+void pciback_do_op(void *data)
+{
+	struct pciback_device *pdev = data;
 	struct pci_dev *dev;
 	struct xen_pci_op *op = &pdev->sh_info->op;
-
-	if (unlikely(!test_bit(_XEN_PCIF_active,
-			       (unsigned long *)&pdev->sh_info->flags))) {
-		pr_debug("pciback: interrupt, but no active operation\n");
-		goto out;
-	}
 
 	dev = pciback_get_pci_dev(pdev, op->domain, op->bus, op->devfn);
 
@@ -65,10 +72,25 @@
 	else
 		op->err = XEN_PCI_ERR_not_implemented;
 
+	/* Tell the driver domain that we're done. */ 
 	wmb();
 	clear_bit(_XEN_PCIF_active, (unsigned long *)&pdev->sh_info->flags);
 	notify_remote_via_irq(pdev->evtchn_irq);
 
-      out:
+	/* Mark that we're done */
+	wmb();
+	clear_bit(_PDEVF_op_active, &pdev->flags);
+
+	/* Check to see if the driver domain tried to start another request
+	 * in between clearing _XEN_PCIF_active and clearing _PDEVF_op_active */
+	test_and_schedule_op(pdev);
+}
+
+irqreturn_t pciback_handle_event(int irq, void *dev_id, struct pt_regs *regs)
+{
+	struct pciback_device *pdev = dev_id;
+
+	test_and_schedule_op(pdev);
+
 	return IRQ_HANDLED;
 }
diff -r 1020c52c58c1 -r 1c4d731a68ef linux-2.6-xen-sparse/drivers/xen/pciback/xenbus.c
--- a/linux-2.6-xen-sparse/drivers/xen/pciback/xenbus.c	Sat Apr 22 09:41:53 2006
+++ b/linux-2.6-xen-sparse/drivers/xen/pciback/xenbus.c	Tue Apr 25 16:58:33 2006
@@ -30,6 +30,8 @@
 	pdev->evtchn_irq = INVALID_EVTCHN_IRQ;
 	pdev->be_watching = 0;
 
+	INIT_WORK(&pdev->op_work, pciback_do_op, pdev);
+
 	if (pciback_init_devices(pdev)) {
 		kfree(pdev);
 		pdev = NULL;
@@ -46,6 +48,11 @@
 	/* Ensure the guest can't trigger our handler before removing devices */
 	if (pdev->evtchn_irq != INVALID_EVTCHN_IRQ)
 		unbind_from_irqhandler(pdev->evtchn_irq, pdev);
+
+	/* If the driver domain started an op, make sure we complete it or
+	 * delete it before releasing the shared memory */
+	cancel_delayed_work(&pdev->op_work);
+	flush_scheduled_work();
 
 	if (pdev->sh_info)
 		xenbus_unmap_ring_vfree(pdev->xdev, pdev->sh_info);