Random "Unexpected IOM status" messages in ci-kit "psl -syserr"

[canthony]

03:09:28 1000135  5 disk_control: Unexpected IOM status 400000000000000000000000 for dska (channel A11).

The number and timing of the messages vary from run to run, suggesting a race condition.

Running ci-kit in a single CPU configuration results in no messages, suggesting that the race condition is in Multics and not the simulator.

The message is generated by procedure check_stat in disk_control.pl1. check_stat is called by two procedures: "run" and "disk_inter".

The "run" procedure contains the comment:

/* Poll for disk completion.  This is required for allocation lock checks, and
   during run_locks from page control, since both are run masked, and this
   polling is the only way we would see disk completion.  This race hazard
   on normal 15-seconds run_locks will produce some interrupts without
   terminate status, but you can't win them all.  It may also produce some
   situations of interrupt wile not active. */

It is not known that this is the source of the message.

[Eric Swenson]

​https://s3.amazonaws.com/eswenson-multics/public/mcrs/MCR10186.pdf