Serious issue with serial console in 5.4

[Marc Olzheim]

On Thu, Jul 21, 2005 at 10:56:54AM +0200, Eirik verby wrote:
> >>>Fatal trap 12: page fault while in kernel mode
> >>>cpuid = 1; apic id = 00
> >>>fault virtual address   = 0x1c
> >>>fault code              = supervisor write, page not present
> >>>instruction pointer     = 0x8:0xc0620b5f
> >>>stack pointer           = 0x10:0xdadbd988
> >>>frame pointer           = 0x10:0xdadbd994
> >>>code segment            = base 0x0, limit 0xfffff, type 0x1b
> >>>                      = DPL 0, pres 1, def32 1, gran 1
> >>>processor eflags        = interrupt enabled, resume, IOPL = 0
> >>>current process         = 51999 (getty)
> >>>trap number             = 12
> >>>panic: page fault
> >>>cpuid = 1
> >>>boot() called on cpu#0
> >>>Uptime: 66d11h24m50s
> >>>
> >>
> >>The above panic will show up occasionally when logging out from a
> >>serial console (i.e. ctrl-D, logout, exit, whatever). This is
> >>EXTREMELY BAD, as it will crash an otherwise perfectly healthy box at
> >>random - and renders the serial console useless.
> >>
> >>Robert Watson confirmed this to be an issue on the 10th of April.
> >>
> >>Anyone??
> >>
> >
> >You might have to wait until 6.0-R since fixing it seems to require
> >infrastructure changes that cannot easily be backported to 5.x.
> 
> With all due respect - if this is (and I'm assuming it is, because it  
> happens on all the servers I'm serial-controlling) an omnipresent  
> problem on 5.x, I daresay it should warrant some more attention.  
> Having unsafe serial terminal support that can bring down your system  
> like that defies much of the point of having serial terminal support  
> in the first place.
> 
> However, since I seem to be the only one who has noticed this,  
> perhaps I'm the last person on earth to routinely use serial terminal  
> switches instead of KVM switches to do my admin work?

Nope, I use them a lot as well, but only if there are problems. Why
would you login on a serial console if there's ssh ;-)

So that would explain why I haven't seen the issue yet.
Do you have a debugger trace ? It seems very similar to my last
remaining issue
(http://www.stack.nl/~marcolz/FreeBSD/showstoppers.html), namely

http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/83375

i.e. someting going wrong in pty cloning and cleanup...

Marc
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