setrq panic

[vax]

I am running 4.2 BSD on a VAX 750.  About once a day, our
system will crash with a setrq panic.  Sometimes the update()
from panic succeeds; sometimes it fails with a panic from
sleep.  The dump always indicates that the kernel has called
setrq from syscall after finding runrun set.  The panic is
supposed to indicate that p_rlink is nonzero for the proc structure
passed to setrq.  In fact, the proc referenced by u.u_procp
does have p_rlink set, and this is proc passed by syscall to setrq.
Since the parameter to setrq is not placed on the stack, I have
not been able to find it in the dump (yet).  One bizzare aspect
to the whole thing is that syscall is always just finishing up
with a getpagesize() SVC!

Other miscellaneous data:  The system has 2 Ampex Capricorn Disk Drives,
an SI disk controller, an Ampex tape drive, a line printer, and 4
DZ's.  The disk controller is attached to the MASBUS and the rest
of the peripherals are attached to the UNIBUS.  We have an out of
rev back plane, but no evidence implicating it directly, but of
course, until the problem is solved we can't be sure.

I would greatly appreciate any advice as to what the problem
might be or what to look at or what to look for.

If there is interest, I will post results to the net.

			Thanks in advance,
			Pat Keziah

			hao!ascvax!pjk

			Ampex Switcher Company
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