Machine freezes on modem ring

[Nate Eldredge]

Hi all,

I have an odd problem with my FreeBSD box.  I have an external serial 
modem connected, and whenever the phone rings, the system freezes 
momentarily.  No mouse movement, etc.  To diagnose it, I wrote a program 
that calls gettimeofday continuously, and when the phone rings there is 
about a 2 second interval between loops.  This corresponds roughly to the 
time of each ring.

It is certainly related to the serial modem because disconnecting the 
modem from the phone line fixes it.  The modem works fine otherwise.

There is no process listening on that port when I do this.  (faxgetty from 
hylafax was there, but I took it out of /etc/ttys, init q, and the 
behavior persists.)  Therefore it is either a kernel or a hardware 
problem.  I could try booting another OS to see if that's affected as 
well, but I'd rather not take this box down.

The machine is a single-cpu Opteron running 6.2-RELEASE/amd64.  The modem 
is a generic external serial type and is connected to a serial port on the 
motherboard.  There are two ports and the problem appears with the modem 
connected to either one.

Jan  5 14:55:49 vulcan kernel: sio0: <16550A-compatible COM port> port 
0x3f8-0x3ff irq 4 flags 0x10 on acpi0
Jan  5 14:55:49 vulcan kernel: sio0: type 16550A
Jan  5 14:55:49 vulcan kernel: sio1: <16550A-compatible COM port> port 
0x2f8-0x2ff irq 3 on acpi0
Jan  5 14:55:49 vulcan kernel: sio1: type 16550A

The "flags 0x10" for sio0 which was for a serial console setup appears 
irrelevant, since the problem arises on sio1 as well.

Just curious if anyone knows what this could be.  If not, I'll investigate 
further.  Thanks in advance for any ideas.

A personal CC is appreciated on replies, though I read the list as well.

-- 

Nate Eldredge
neldredge at math.ucsd.edu