On Wed, 12 Nov 2003, Duncan Sands wrote:
> I'm getting various oopses in 2.6 due to actconfig being NULL
> unexpectedly in devio.c, namely in these releaseintf and findintif:
> The first oops occurs always at system shutdown. The second oops occurs
> sometimes at system startup. I can "fix" the first one by replacing
> down(&dev->serialize);
> with
> lock_kernel();
> and
> up(&dev->serialize);
> with
> unlock_kernel();
> in releasintf. The logic here is that although usbdev_release takes the BKL,
> it can lose it while sleeping in the down(&dev->serialize) in releaseintf,
> which is not what is intended I guess (and since it eliminates the first oops,
> there must be some truth to this theory). However things are more complicated
> because usb_driver_release_interface(&usbdevfs_driver, iface) can also sleep,
> which might also cause problems. I haven't analysed this yet. Maybe this
> change also fixed the second oops, but since that one only occurs about one
> time in four, it is hard to be sure.
>
> I will of course look into this further, but I thought I would mention it now in
> case anyone has any ideas.
Usbfs is full of locking errors. In particular, there's no excuse for it
holding the BKL.
In this case, the simplest solution is simply to insert a test for
actconfig != NULL before it gets dereferenced. To make certain that
actconfig won't change out from under you, be sure to hold dev->serialize
during that test.
The real problem is that usbfs is trying to unbind a driver after usbcore
has already done so on its behalf. A better fix would be to repair
driver_disconnect() and the USBDEVFS_DISCONNECT case in proc_ioctl()
to make them use the
test_and_clear_bit(intf, &ps->ifclaimed)
test as they should.
Alan Stern
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