SUMMARY: panic: swtch

From: Morten K. Barfoed (
Date: Fri Feb 03 1995 - 04:45:54 CST

Dear sunmanagers,

My original posting:

------ Begin Included Message -----
- Dear Sun-managers.
- Today, my SUN 470-server, running SunOS 4.1.3 went
- down with the laconic message 'panic: swtch'.
- What does it mean, and how to avoid it ??
------ End Included Message -----

Thanks to,

Mike wrote:

$We chased intermittent occurrences of this on a 490 running 4.1.2 for
$months. Eventually Sun came though with patch 101134 (it was probably
$generated for our client). The description says the cause is
$serial port activity, but it was likely that in this case the cause was
$high volumes of garbage network activity. They had terminal servers
$with very long serial lines attached, and if terminals were powered off they'd
$start generating rubbish, which would cause the servers to automatically
$call the Sun. 101134 (or its pre-release version) definitely fixed a
$a problem in the context switching code."


$Well, I can help you with the first part at any rate. swtch is the
$"routine" that is called to do a context switch. In other words, you'll
$see it at the bottom of the call graph when you do a trace back of the
$kernel stack for a process. ($<traceall in adb -k for instance)
$A panic there means that something about the context it was about to
$unload or load was bogus, so it panic'ed.
$My guess is that there is a patch lurking somewhere with your name on it.

Eric Parr sent me a description of the patch:

$Patch-ID# 101134-03
$Keywords: point patch panic serial ports swtch
$Synopsis: SunOS 4.1.2, 4.1.3: point patch for rare panic due to
$serial port load
$Date: Aug/02/94
$Solaris Release: 1.1
$SunOS release: 4.1.2, 4.1.3, 4.1.3C...


I got hold of the patch, and hopefully that's it.

Thanks again mates !

Morten Krabbe Barfoed

Danish Space Research Institute phone: +45 42 88 22 77 (switch-board)
Gl. Lundtoftevej 7 phone: +45 45 87 40 77 - 161 (direct)
DK 2800 Lyngby FAX: +45 45 93 02 83
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