[Info-vax] Nonexisting "Owner process" of a device.

[Michael Moroney]

mcleanjoh at gmail.com writes:

>I can see one way that this might happen ...

>Process A requests that some other process (let's call it B) provide an I/O
>device or channel and then process A terminates without telling process B 
>to deassign the device or channel.

Pretty much.
If I recall correctly, the original problem went somewhat like this:

Process A assigns a channel/allocates some device that is not normally
shareable (such as a terminal, whether virtual or real). Since the
device isn't shareable (such as a disk), the owner PID field gets set
to this process' PID.

Process B, using the SHARE privilege, assigns a channel to the same device
and does some IO. A remains the owner.

Process A deassigns the channel/logs out/similar, but since the device
reference count doesn't go to 0 (because of B), certain cleanup
activities (including zeroing of the owner PID) doesn't happen.

Once A logs out, the owner PID references a nonexistent process.

When B deassigns its channel, for some reason the PID field does
not get set to 0 because it's not B's PID.  In the original problem,
the reference count to the device does not go to 0 for some reason, so
now the device is "owned" by a nonexistent process with a phantom
reference to it.