In some email I received from Matthew Jacob, sie wrote:
[...]
> The normal path was (roughly) expected to be:
> 
> isp_pci_intr
>   isp->isp_onintstack = 1;
>     isp_intr
>     ...
>     (SCSI midlayer)
>       ...
>       isprequest
> 	isp_start
> 	(exception condition causes)
> 	  isp_mboxcmd
> 	    if (isp->isp_onintstack)
> 	      POLL
> 	    else
> 	      tsleep
> 	  ...
> 
> 
> The problem that broke me was:
> 
> isp_pci_intr
>   isp->isp_onintstack = 1;
>     isp_intr
>     ...
>     (SCSI midlayer- called with BUSY status on SCSI command)
>       (kthread schedule of scsi_completion, which then does
>       callout_reset so that in 1 second, essentially)
>       ...
>       isprequest
> 	isp_start
> 	(exception condition causes)
> 	  isp_mboxcmd
> 	    if (isp->isp_onintstack)
> 	      POLL
> 	    else
> 	      tsleep
> 	  ...
> 
> But because isp->isp_onintstack isn't set, I called tsleep. Boom.

Oh, that's just plain _yuck_.

NetBSD needs, at the very least, an interrupt kthread for kernel callouts.
Preferably one for each callout which gets activated.

Meanwhile, you can't push whatever it is you're doing back and force a new
interrupt for the ISP controller, can you?  Or even fake one happening...

Darren