- Instead of waiting forever to get a vnode in getnewvnode() wait for

one to become available for one second and then return ENFILE.  We
   can run out of vnodes, and there must be a hard limit because without
   one we can quickly run out of KVA on x86.  Presently the system can
   deadlock if there are maxvnodes directories in the namecache.  The
   original 4.x BSD behavior was to return ENFILE if we reached the max,
   but 4.x BSD did not have the vnlru proc so it was less profitable to
   wait.

sys/kern/vfs_subr.c

@@ -815,13 +815,15 @@ getnewvnode(tag, mp, vops, vpp)
 	/*
 	 * Wait for available vnodes.
 	 */
-	while (numvnodes > desiredvnodes) {
+	if (numvnodes > desiredvnodes) {
 		if (vnlruproc_sig == 0) {
 			vnlruproc_sig = 1;      /* avoid unnecessary wakeups */
 			wakeup(vnlruproc);
 		}
 		msleep(&vnlruproc_sig, &vnode_free_list_mtx, PVFS,
 		    "vlruwk", hz);
+		if (numvnodes > desiredvnodes)
+			return (ENFILE);
 	}
 	numvnodes++;
 	mtx_unlock(&vnode_free_list_mtx);