> Some time ago I know there was a problem with several ports with processes
> occassionally hanging in a disk-wait (in vflushbuf). Does anyone know whether
> this problem was ever resolved?

It wasn't, though I've found one possible cause of this last time it happened
on my sparc (yesterday :-)

Can you please try this patch (which isn't on the release tree yet) and
see what it does for you:


----snip----
Index: vfs_bio.c
===================================================================
RCS file: /a/cvsroot/src/sys/kern/vfs_bio.c,v
retrieving revision 1.43
retrieving revision 1.44
diff -c -r1.43 -r1.44
*** vfs_bio.c	1996/04/22 01:38:59	1.43
--- vfs_bio.c	1996/06/11 11:15:36	1.44
***************
*** 1,4 ****
! /*	$NetBSD: vfs_bio.c,v 1.43 1996/04/22 01:38:59 christos Exp $	*/
  
  /*-
   * Copyright (c) 1994 Christopher G. Demetriou
--- 1,4 ----
! /*	$NetBSD: vfs_bio.c,v 1.44 1996/06/11 11:15:36 pk Exp $	*/
  
  /*-
   * Copyright (c) 1994 Christopher G. Demetriou
***************
*** 275,281 ****
  bwrite(bp)
  	struct buf *bp;
  {
! 	int rv, sync, wasdelayed;
  
  	/*
  	 * Remember buffer type, to switch on it later.  If the write was
--- 275,281 ----
  bwrite(bp)
  	struct buf *bp;
  {
! 	int rv, sync, wasdelayed, s;
  
  	/*
  	 * Remember buffer type, to switch on it later.  If the write was
***************
*** 293,298 ****
--- 293,299 ----
  	wasdelayed = ISSET(bp->b_flags, B_DELWRI);
  	CLR(bp->b_flags, (B_READ | B_DONE | B_ERROR | B_DELWRI));
  
+ 	s = splbio();
  	if (!sync) {
  		/*
  		 * If not synchronous, pay for the I/O operation and make
***************
*** 307,314 ****
  	}
  
  	/* Initiate disk write.  Make sure the appropriate party is charged. */
- 	SET(bp->b_flags, B_WRITEINPROG);
  	bp->b_vp->v_numoutput++;
  	VOP_STRATEGY(bp);
  
  	if (sync) {
--- 308,316 ----
  	}
  
  	/* Initiate disk write.  Make sure the appropriate party is charged. */
  	bp->b_vp->v_numoutput++;
+ 	splx(s);
+ 	SET(bp->b_flags, B_WRITEINPROG);
  	VOP_STRATEGY(bp);
  
  	if (sync) {
***************
*** 322,331 ****
--- 324,335 ----
  		 * make sure it's on the correct vnode queue. (async operatings
  		 * were payed for above.)
  		 */
+ 		s = splbio();
  		if (wasdelayed)
  			reassignbuf(bp, bp->b_vp);
  		else
  			curproc->p_stats->p_ru.ru_oublock++;
+ 		splx(s);
  
  		/* Release the buffer. */
  		brelse(bp);