KDB over serial port

[Keith Owens]

On Thu, 12 Dec 2002 17:52:33 +0530, 
"Sachin P Sant" <ssant at in.ibm.com> wrote:
>I am having a problem with KDB over serial port. These are the steps i
>follow ....
>
>1] Enter KDB via serial port using Ctrl - A sequence
>2] Put breakpoint using bp command [ bp c011b950 (do_fork routine ) ]
>3] give a go command.
>4] When the breakpoint is hit , the control is passed to the serial
>console. But after this i am not able to do anything on the serial console.
>My keyboard/mouse dosen't respond. I can see the KDB prompt , but can't do
>anything with it.  Also this problem is very inconsistent .Some time the
>hang occurs at the first bp hit and sometime it occurs when the breakpoint
>hits 7th time. Can the polling routine for serial console be a culprit here

Try attaching the keyboard directly to the machine and not over a KVM.
Or try another keyboard.  Some keyboards and/or KVMs do not handle
polling mode I/O very well.

The other possibility is a known race condition in kdb when two cpus
hit the same break point at the "same" time.  Both cpus try to drive
into kdb and they deadlock.  I do not have a clean fix for this, except
to avoid breakpoints in highly used code.