Swapping deadlock due to aic/scsi errors?

[Justin T. Gibbs]

> We have a reproducible bug characterized by the system
> becoming unresponsive (but db may be entered).
> System is based on FreeBSD 4.7 (i386)
> Using the aic79xx scsi driver.

If you are using the stock aic79xx driver found in 4.7, I would
start by pulling in the latest 4.X aic79xx driver into your system.

> I would like to add some debugging to detect the lost command 
> and possibly retry it.  Can someone suggest where the lost
> command is supposed to be detected, and where the retry is 
> supposed to occur.

The "lost command" is supposed to be detected by the timeout
handler in the ahd driver.  The timeout handler just forces
a bus reset which should cause the command to be returned to
the SCSI layer and then retried.  It's not clear to me why
this might not be happening, but the ahd driver was relatively
green in 4.7 and you may just be tripping over a known (and
later corrected) bug manifesting itself in an unusual way.

--
Justin