Re: crash in tmpfs_itimes since vmlocking2 merge

[Antti Kantee <pooka%cs.hut.fi@localhost>]

On Mon Jan 21 2008 at 15:33:41 -0600, David Young wrote:
> The following crash during shutdown is fairly repeatable.  It began
> to happen after I updated to -current from pre-vmlocking2 sources.
> It may be necessary to reproduce my thicket of null mounts in order to
> reproduce the crash,
> 
> /dev/wd0a on / type ffs (read-only, local)
> tmpfs on /dev type tmpfs (union, local)
>
> [snip]
> 
> unmounting /dev (tmpfs)...
> 
> unmounting / (/dev/wd0a)...uvm_fault(0xc0398760, 0xc6984000, 1) -> 0xe
> 
> kernel: supervisor trap page fault, code=0

You are trying to modify the vnode for /dev/wd0a to update the access time
info, but tmpfs has been garbage collected already when unmounting /dev.

This is the problem of forcibly unmounting a file system with device
vnodes on it.  There was a small discussion about splitting specfs
into two layers: one for the "host" file system (tmpfs in this case)
and one for the actual device info (specfs).  Then you could rip the
"host" part out without affecting the device part before the device goes
inactive and can be safely put to rest.

-- 
Antti Kantee <pooka%iki.fi@localhost>                     Of course he runs 
NetBSD
http://www.iki.fi/pooka/                          http://www.NetBSD.org/
    "la qualité la plus indispensable du cuisinier est l'exactitude"