When loading a driver that is a subclass of another driver don't set the

devclass's parent pointer if the two drivers share the same devclass.  This
can happen if the drivers use the same new-bus name.  For example, we
currently have 3 drivers that use the name "pci": the generic PCI bus
driver, the ACPI PCI bus driver, and the OpenFirmware PCI bus driver.  If
the ACPI PCI bus driver was defined as a subclass of the generic PCI bus
driver, then without this check the "pci" devclass would point to itself
as its parent and device_probe_child() would spin forever when it
encountered the first PCI device that did have a matching driver.

Reviewed by:	dfr, imp, new-bus@

1 files changed, 11 insertions, 1 deletions

diff --git a/sys/kern/subr_bus.c b/sys/kern/subr_bus.c
index 7f7bb93..b19be54 100644
--- a/sys/kern/subr_bus.c
+++ b/sys/kern/subr_bus.c
@@ -781,7 +781,17 @@ devclass_find_internal(const char *classname, const char *parentname,
 
 		bus_data_generation_update();
 	}
-	if (parentname && dc && !dc->parent) {
+
+	/*
+	 * If a parent class is specified, then set that as our parent so
+	 * that this devclass will support drivers for the parent class as
+	 * well.  If the parent class has the same name don't do this though
+	 * as it creates a cycle that can trigger an infinite loop in
+	 * device_probe_child() if a device exists for which there is no
+	 * suitable driver.
+	 */
+	if (parentname && dc && !dc->parent &&
+	    strcmp(classname, parentname) != 0) {
 		dc->parent = devclass_find_internal(parentname, 0, FALSE);
 	}