--- linux-2.6.19.vanilla/drivers/pci/search.c	2006-11-29 21:57:37.000000000 +0000
+++ linux-2.6.19/drivers/pci/search.c	2006-12-29 13:58:51.000000000 +0000
@@ -193,6 +193,17 @@
 	struct pci_dev *dev;
 
 	WARN_ON(in_interrupt());
+
+	/*
+	 * pci_find_subsys() can be called on the ide_setup() path, super-early
+	 * in boot.  But the down_read() will enable local interrupts, which
+	 * can cause some machines to crash.  So here we detect and flag that
+	 * situation and bail out early.
+	 */
+	if(unlikely(list_empty(&pci_devices))) {
+		printk(KERN_INFO "pci_find_subsys() called while pci_devices is still empty\n");
+		return NULL;
+	}
 	down_read(&pci_bus_sem);
 	n = from ? from->global_list.next : pci_devices.next;
 
@@ -259,6 +270,16 @@
 	struct pci_dev *dev;
 
 	WARN_ON(in_interrupt());
+	/*
+	 * pci_get_subsys() can potentially be called by drivers super-early
+	 * in boot.  But the down_read() will enable local interrupts, which
+	 * can cause some machines to crash.  So here we detect and flag that
+	 * situation and bail out early.
+	 */
+	if(unlikely(list_empty(&pci_devices))) {
+		printk(KERN_NOTICE "pci_get_subsys() called while pci_devices is still empty\n");
+		return NULL;
+	}
 	down_read(&pci_bus_sem);
 	n = from ? from->global_list.next : pci_devices.next;