Re: umount/ls panic

["Thomas E. Spanjaard" <tgen@xxxxxxxxxxxxx>]

Nicolas Thery wrote:
> 2007/10/4, Petr Janda <elekktretterr@exemail.com.au>:
>
> > Hi Matt and the rest,
> > I just discovered a new bug. What happened is this:
> >
> > ad3s2 is mount on /mnt/windows
> >
> > i mounted fat32 fs (ad3s3) over /mnt/windows
> >
> > cd /mnt/windows, then force umount of /mnt/windows. if you dont get a panic
> > yet, try ls the directory you are in (mnt windows) and get this panic:
> >
> > http://www.punchyouremployer.com/images/p1000675.jpg
>
>
> This bug is not related to fat32.  It can for example be reproduced with /proc:
>
> cd /proc
> umount -f /proc
> ls (or any external command)
>
> It can also be reproduced w/o force unmount:
>
> sleep 30 &
> cd /proc/$!
> ... wait for 30s or kill the sleep process ...
> ls (or any external command)
>
> When forking ls, fdcopy() calls vref() on fd_cdir but the latter was
> inactivated earlier during unmounting (vflush()).  This triggers the
> assertion in vref().
>
> I don't know how to fix this.  As an experiment, I tried setting
> fd_cdir to NULL if VINACTIVE is set but this triggers a crash at
> boot-time.  Maybe the assertion should be relaxed, for this case only,
> to:
>
> KKASSERT(vp->v_sysref.refcnt > 0 && (vp->v_flag & VFREE) == 0);
>
> Any advice?

Ideally, the umount shouldn't be able to succeed because it's still open 
as CWD for someone.

Cheers,
--
        Thomas E. Spanjaard
        tgen@netphreax.net

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