Add required BUF_KERNPROC to flushchainbuf() to disassociate the

current process from the exclusive lock prior to initiating I/O.

    This fixes a panic related to swap-backed VN disks

Reviewed by:	Alan Cox <alc@cs.rice.edu>, David Greenman <dg@root.com>

sys/vm/vm_pager.c

@@ -566,6 +566,7 @@ flushchainbuf(struct buf *nbp)
 		nbp->b_bufsize = nbp->b_bcount;
 		if ((nbp->b_flags & B_READ) == 0)
 			nbp->b_dirtyend = nbp->b_bcount;
+		BUF_KERNPROC(nbp);
 		VOP_STRATEGY(nbp->b_vp, nbp);
 	} else {
 		biodone(nbp);