double fault

[Stone, Joshua I]

>From: Roland McGrath [mailto:roland@redhat.com] 
>
>The stack overflow notion sounds plausible.  To investigate 
>that angle, one
>thing to try comes to mind off hand.  In each probe that might 
>be hitting,
>stick some %{ ... %} code to do a "stack getting small" check. 
> It can do
>something like:
>
>	unsigned left = (unsigned)regs & 0xfff;
>	if (left < 256) panic("stack getting close");
>
>That might manage to print out a full oops with backtrace 
>details that show
>the cascade of page fault frames or whatever the situation actually is.
>
>
>Thanks,
>Roland
>

I tried the code you gave (using CONTEXT->regs), but I don't understand
how that computes how much stack space is left.  Shouldn't it be
CONTEXT->regs->esp?  And even then, you can see the two esp's from the
register dumps I gave - the first would have triggered your panic, and
the second wouldn't.  Am I missing something?

Anyway, I tried it both ways.  It immediately panics, but there's no
oops info.  It just says "Kernel panic - not syncing".  I added a
dump_stack call, but that all looks innocent.

Is there a way I can get the double-fault to print a full oops, with a
stack trace?

I'm pretty new to kernel-debugging, so sorry if I'm asking simple
questions...

Thanks,

Josh