Re: (driver model) bus kset list manipulation bug
From: Hollis Blanchard
Date: Tue Jan 27 2004 - 18:36:42 EST
On Jan 22, 2004, at 1:38 PM, Hollis Blanchard wrote:
I've found a bug in drivers/base/bus.c, where the
bus_type.devices.list is treated as a list of device structs.
bus_type.devices is a kset though, so devices.list should contain
kobjects rather than devices. Here is the diff I've come up with:
[big snip]
@@ -405,7 +405,7 @@
if (bus) {
down_write(&dev->bus->subsys.rwsem);
pr_debug("bus %s: add device
%s\n",bus->name,dev->bus_id);
- list_add_tail(&dev->bus_list,&dev->bus->devices.list);
+
list_add_tail(&dev->kobj.entry,&dev->bus->devices.list);
device_attach(dev);
up_write(&dev->bus->subsys.rwsem);
Here's the problem: dev->kobj is already in use; it's part of the
global devices_subsys kset.
devices_subsys looks like it's only used for two things: global hotplug
policy and suspend. Of the 3 hotplug functions it provides
(dev_hotplug_filter, dev_hotplug_name, and dev_hotplug), 2 of them
refer to bus data or code anyways.
I'm very surprised to see it's used by device_shutdown(). I thought one
of the points of the device tree was to do depth-first-suspend, so e.g
we don't try to suspend a PCI bridge and *then* try to suspend children
of that bridge. Instead we're walking a global list in the reverse
order they were registered. I guess this works because busses are
discovered from the root down, so going backwards will give you the
deepest first.
I see three options, and I like the last best:
- add another kobject to struct device. This will allow a device to be
registered with the global devices_subsys as well as a bus.devices kset
simultaneously.
- change the kset "bus_type.devices" to a normal "list_head*" (which is
how it's being used today, incorrectly). This will preclude some of the
nice kobject/kset functionality however (e.g. see last paragraph
below).
- remove devices_subsys. The hotplug policy is already entirely
bus-specific anyways. The suspend code can be made to use bus
structures as well instead of a global device list (can it?).
The point of all of this is I want to be able to call
device_find("mydevice", &my_bus_type)
device_find() uses kset_find_obj() on the bus_type.devices kset, and
that doesn't work because bus_type.devices isn't a real kset, and it's
not a real kset because you can't register device kobjects in it, and
you can't because those kobjects have already been registered with
devices_subsys. I could call
device_find("mydevice", &devices_subsys.kset)
instead, but I already know what bus my device is on; no need to search
them all...
--
Hollis Blanchard
IBM Linux Technology Center
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