Re: kernel deadlock on fstchg with vnd

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Sun, May 29, 2022 at 01:18:16PM +0200, J. Hannken-Illjes wrote:
> > On 29. May 2022, at 08:30, Michael van Elst <mlelstv%serpens.de@localhost> wrote:
> > 
> > bouyer%antioche.eu.org@localhost (Manuel Bouyer) writes:
> > 
> >> Hello,
> >> do you have an idea on the problem in this thread:
> >> http://mail-index.netbsd.org/port-xen/2022/05/27/msg010213.html
> > [...]
> >> I can't reproduce this when using vnd from userland.
> > 
> > You can replicate it by addressing the block device with vnconfig.
> > 
> > A workaround would be to modify the Xen block script to select the
> > raw device:
> > 
> > vnconfig /dev/r${disk}d $xparams >/dev/null; then
> > 
> > or just the disk name:
> > 
> > vnconfig ${disk} $xparams >/dev/null; then
> 
> Good catch, sys/dev/vnd.c has this:
> 
>   1751  static void
>   1752  vndclear(struct vnd_softc *vnd, int myminor)
>   1753  {
>   1754          struct vnode *vp = vnd->sc_vp;
>   1755          int fflags = FREAD;
>   1756          int bmaj, cmaj, i, mn;
>   1757          int s;
>   1758
>   1759  #ifdef DEBUG
>   1760          if (vnddebug & VDB_FOLLOW)
>   1761                  printf("vndclear(%p): vp %p\n", vnd, vp);
>   1762  #endif
>   1763          /* locate the major number */
>   1764          bmaj = bdevsw_lookup_major(&vnd_bdevsw);
>   1765          cmaj = cdevsw_lookup_major(&vnd_cdevsw);
>   1766
>   1767          /* Nuke the vnodes for any open instances */
>   1768          for (i = 0; i < MAXPARTITIONS; i++) {
>   1769                  mn = DISKMINOR(device_unit(vnd->sc_dev), i);
>   1770                  vdevgone(bmaj, mn, mn, VBLK);
>   1771                  if (mn != myminor) /* XXX avoid to kill own vnode */
>   1772                          vdevgone(cmaj, mn, mn, VCHR);
>   1773          }
> 
> The "skip myself" on lines 1771/1772 is responsible for this behaviour.

Yes and doing the same for block devices avoids the issue.
But Taylor is reluctant to commit this hack.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--