- Only return 1 from sync_vnode() in cases where the vnode is still

at the head of the sync list.  This prevents sched_sync() from
   re-queueing a vnode which may have been freed already.

Discussed with:	kib

sys/kern/vfs_subr.c

@@ -1664,7 +1664,7 @@ restart:
 		vdrop(vp);
 		VFS_UNLOCK_GIANT(vfslocked);
 		mtx_lock(&sync_mtx);
-		return (1);
+		return (*bo == LIST_FIRST(slp));
 	}
 	vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
 	(void) VOP_FSYNC(vp, MNT_LAZY, td);