On Wed, Apr 13, 2005 at 09:40:17PM +0400, Roman Kagan wrote:
> With 2.6.11 and 2.6.12-rc2 (and perhaps a few versions before) usb
> drivers for multi-interface devices, which do
> usb_driver_release_interface() in their disconnect(), make rmmod hang.
>
> It turns out to be due to a bug in drivers/base/bus.c:driver_detach(),
> that iterates over the list of attached devices with
> list_for_each_safe() under an assumption that device_release_driver()
> only releases the current device, while it may also call
> device_release_driver() for other devices on the same list.
A similar problem exists in -mm branch with klists. However, here it
falls into several separate bugs:
1) an obvious typo:
--- linux-2.6.12-rc2-mm3/drivers/usb/core/usb.c~ 2005-04-13
15:13:44.000000000 +0400
+++ linux-2.6.12-rc2-mm3/drivers/usb/core/usb.c 2005-04-13 19:33:54.000000000
+0400
@@ -323,7 +323,7 @@ void usb_driver_release_interface(struct
return;
/* don't disconnect from disconnect(), or before dev_add() */
- if (!klist_node_attached(&dev->knode_driver) &&
!klist_node_attached(&dev->knode_bus))
+ if (klist_node_attached(&dev->knode_driver) &&
klist_node_attached(&dev->knode_bus))
device_release_driver(dev);
dev->driver = NULL;
2) with klists, klist_del() in
drivers/base/dd.c:device_release_driver(), when the latter is called
from drivers/base/dd.c:driver_detach(), doesn't immediately delete
the device from the list, because the node is referenced from the
iteration. Therefore klist_node_attached(&dev->knode_driver) may be
true in disconnect(), and thus can't protect from recursion into
device_release_driver()
3) I'm yet unable to tell if the original problem of multiple list
entries disappearing from under the list iteration also applies to
klists - they seem to be too complex to me...
Roman.
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