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SubjectRe: deadlock in "modprobe -r ohci1394" shortly after "modprobe ohci1394"
Alan Stern wrote:
> Wait a minute. Above you agreed that the problem was caused by knodemgrd
> attempting to rescan the host's _parent_. So which is the focus of the
> deadlock: the host or its parent?

The parent of the hpsb_host.

ohci1394 works on a pci_dev which contains a dev, let's call it A.

ieee1394 has a hpsb_host which contains a dev, let's call it B. B's
parent is A. Then there is one or more node_entry with dev C whose
parent is B, end unit_directory with dev D whose parent is C.

The bus of devices B, C, D is set to be ieee1394_bus_type, and that's
what knodemgrd is scanning.

knodemgrd blocks on the semaphore of the parent of B because
driver_detach took the semaphore of A (and of the parent of A if there
is one).

> If I understand all this, you've got an hpsb_host, directly below which
> are one or more node_entry's, below each of which may be some
> unit_directory's. Right?


> But how is this relevant if the problem is caused by knodemgrd trying to
> rescan the hpsb_host's parent?

It's rescanning just the hpsb_host, but you surely got the picture now.

> Is the problem caused by the fact that some of these struct device's
> aren't bound to a driver? Remember, bus_rescan_devices() will skip over
> anything that already has a driver. Could you solve your problem by
> adding a do_nothing driver that would bind to these otherwise unused
> devices?

Excellently, that's what I will try in a minute. It is surely intended
that the hpsb_host can get a driver bound too, but as I mentioned, we
don't have a driver which needs this capability and I don't foresee any
such driver.

Thanks for the directions.
Stefan Richter
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