[src/trunk]: src/sys/netinet Get rid of meaningless RTF_UP check from ip_hres...

[ozaki-r <ozaki-r%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/5ddb37149675
branches:  trunk
changeset: 344764:5ddb37149675
user:      ozaki-r <ozaki-r%NetBSD.org@localhost>
date:      Mon Apr 18 01:28:06 2016 +0000

description:
Get rid of meaningless RTF_UP check from ip_hresolv_output

The check is meaningless because
- An obtained rtentry is ensured that it's always RTF_UP by rtcache,
  rtalloc1 and rtlookup. If the rtentry isn't changed (i.e., RTF_UP gets
  dropped) during processing, the check should be unnecessary
- Even if not, i.e., an obtained rtentry can be changed during processing,
  checking only at the point doesn't help; the rtentry can be changed after
  the check

Instead we have to ensure that RTF_UP isn't dropped if someone is using it
somehow. Note that we already ensure that a rtentry being used isn't freed
by rt_refcnt.

Proposed on tech-kern and tech-net.

diffstat:

 sys/netinet/ip_output.c |  46 ++++++++--------------------------------------
 1 files changed, 8 insertions(+), 38 deletions(-)

diffs (75 lines):

diff -r a8ee94a4aaf6 -r 5ddb37149675 sys/netinet/ip_output.c
--- a/sys/netinet/ip_output.c   Sun Apr 17 19:54:32 2016 +0000
+++ b/sys/netinet/ip_output.c   Mon Apr 18 01:28:06 2016 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: ip_output.c,v 1.248 2016/01/20 22:12:22 riastradh Exp $        */
+/*     $NetBSD: ip_output.c,v 1.249 2016/04/18 01:28:06 ozaki-r Exp $  */
 
 /*
  * Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
@@ -91,7 +91,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: ip_output.c,v 1.248 2016/01/20 22:12:22 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: ip_output.c,v 1.249 2016/04/18 01:28:06 ozaki-r Exp $");
 
 #ifdef _KERNEL_OPT
 #include "opt_inet.h"
@@ -202,50 +202,20 @@
  * calling ifp's output routine.
  */
 int
-ip_hresolv_output(struct ifnet * const ifp0, struct mbuf * const m,
-    const struct sockaddr * const dst, struct rtentry *rt00)
+ip_hresolv_output(struct ifnet * const ifp, struct mbuf * const m,
+    const struct sockaddr * const dst, struct rtentry *rt0)
 {
        int error = 0;
-       struct ifnet *ifp = ifp0;
-       struct rtentry *rt, *rt0, *gwrt;
+       struct rtentry *rt = rt0, *gwrt;
 
 #define RTFREE_IF_NEEDED(_rt) \
-       if ((_rt) != NULL && (_rt) != rt00) \
+       if ((_rt) != NULL && (_rt) != rt0) \
                rtfree((_rt));
 
-       rt0 = rt00;
-retry:
-       if (!ip_hresolv_needed(ifp)) {
-               rt = rt0;
+       if (!ip_hresolv_needed(ifp))
                goto out;
-       }
-
-       if (rt0 == NULL) {
-               rt = NULL;
-               goto out;
-       }
-
-       rt = rt0;
 
-       /*
-        * The following block is highly questionable.  How did we get here
-        * with a !RTF_UP route?  Does rtalloc1() always return an RTF_UP
-        * route?
-        */
-       if ((rt->rt_flags & RTF_UP) == 0) {
-               rt = rtalloc1(dst, 1);
-               if (rt == NULL) {
-                       error = EHOSTUNREACH;
-                       goto bad;
-               }
-               rt0 = rt;
-               if (rt->rt_ifp != ifp) {
-                       ifp = rt->rt_ifp;
-                       goto retry;
-               }
-       }
-
-       if ((rt->rt_flags & RTF_GATEWAY) == 0)
+       if (rt == NULL || (rt->rt_flags & RTF_GATEWAY) == 0)
                goto out;
 
        gwrt = rt_get_gwroute(rt);