Swapping deadlock due to aic/scsi errors?

[Don Bowman]

> From: Dave Dolson [mailto:ddolson at sandvine.com]
 ...
> > 
> > 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.
> 
> Are you referring to the timeout handler ahd_timeout() ?
> Are the commmands retried from ahd_reset_channel() ?
> (It looks more like they're simply aborted.)
> 
> Aside: Am I correct in believing that ahd_execute_scb() is called 
> for every command to the drive?

It appears that if we set vm.swap_async_max=64 with sysctl, that 
the problem may no longer be reproducible. The default value seems
to be 4. The system is deadlocking looking for these async buffers.

Does this make sense?