Re: HEADSUP: New pts code triggers panics on amd64 systems.

On 2006-02-07 13:26, Robert Watson <rwatson@xxxxxxxxxxx> wrote:
On Tue, 7 Feb 2006, Giorgos Keramidas wrote:
On 2006-02-01 15:55, Steve Kargl <sgk@xxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
After a binary search, I have determined that the new pts code is
triggering kernel panics on an AMD64 system.

It also makes syscons unusable here.

I just rebuilt a HEAD snapshot from today's latest CVSup, installed it
in /dev/ad0s1a (my test partition), and the behavior is still the same
as a few days ago:

- single user mode shell works fine

- in multiuser mode, when syscons reaches a login prompt
i have to press RET twice to see the last line

It seems that something is broken in the way syscons detects whether an
output line should be flushed out, but I'm not sure.

A snapshot from -D '2006/01/26 01:30:00 UTC' works fine (just before the
first pts change).

I don't know how to debug this or provide more useful feedback, but I'll
look at the diffs later today, when I'm done with $REALJOB stuff.

Does the instability occur if kern.pts.enable=0, or only when
kern.pts.enable=1? If 0, if you back out the user space changes but leave
tty_pts.c compiled into the kernel, do the instability issues persist? How
about with the kernel code compiled out, but the user space code in place?

Basically, it would be good to know if what you're seeing is a property of
the pts code being in the kernel at all, or a property of it actually in
use.

I'm not sure if what I see is a pts side-effect. I rebuilt a snapshot
of HEAD again today, and discovered something else that may help us
track this down.

A few more observations, in case they prove helpful to someone more
acquainted with the way syscons output is supposed to work:

- If I keep hitting Scroll-Lock again and again, then syscons output
*does* eventually appear.

- If I type stuff without seeing it and then press RETURN twice, the
previous from last line *does* appear in my terminal.

- When pressing CTRL-ALT-ESC, the debugger starts normally, but after
typing many times commands that have large output, i.e.:

show witness

the console locks up entirely.

This looks like a locking problem, instead of a pts/syscons one :-/

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