Finally remove the kernel lock from IPv6 neighbor discovery. ND6

entries in rt_llinfo are protected either by exclusive netlock or
the ND6 mutex.  The performance critical lookup path in nd6_resolve()
uses shared netlock, but is not lockless.  In contrast to ARP it
grabs the mutex also in the common case.
tested by Hrvoje Popovski; with and OK kn@

diff --git a/sys/netinet6/nd6.c b/sys/netinet6/nd6.c
index fd3836a..8ddde15 100644 (file)
--- a/sys/netinet6/nd6.c
+++ b/sys/netinet6/nd6.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: nd6.c,v 1.279 2023/05/12 12:42:16 bluhm Exp $ */
+/*     $OpenBSD: nd6.c,v 1.280 2023/05/13 16:27:59 bluhm Exp $ */
 /*     $KAME: nd6.c,v 1.280 2002/06/08 19:52:07 itojun Exp $   */
 
 /*
@@ -306,7 +306,7 @@ nd6_llinfo_timer(struct rtentry *rt)
        struct sockaddr_in6 *dst = satosin6(rt_key(rt));
        struct ifnet *ifp;
 
-       NET_ASSERT_LOCKED();
+       NET_ASSERT_LOCKED_EXCLUSIVE();
 
        if ((ifp = if_get(rt->rt_ifidx)) == NULL)
                return 1;
@@ -557,9 +557,11 @@ nd6_lookup(const struct in6_addr *addr6, int create, struct ifnet *ifp,
                            rtableid);
                        if (error)
                                return (NULL);
+                       mtx_enter(&nd6_mtx);
                        ln = (struct llinfo_nd6 *)rt->rt_llinfo;
                        if (ln != NULL)
                                ln->ln_state = ND6_LLINFO_NOSTATE;
+                       mtx_leave(&nd6_mtx);
                } else
                        return (NULL);
        }
@@ -665,7 +667,7 @@ nd6_free(struct rtentry *rt)
        struct in6_addr in6 = satosin6(rt_key(rt))->sin6_addr;
        struct ifnet *ifp;
 
-       NET_ASSERT_LOCKED();
+       NET_ASSERT_LOCKED_EXCLUSIVE();
 
        ifp = if_get(rt->rt_ifidx);
 
@@ -705,6 +707,8 @@ nd6_nud_hint(struct rtentry *rt)
        struct llinfo_nd6 *ln;
        struct ifnet *ifp;
 
+       NET_ASSERT_LOCKED_EXCLUSIVE();
+
        ifp = if_get(rt->rt_ifidx);
        if (ifp == NULL)
                return;
@@ -990,8 +994,10 @@ nd6_ioctl(u_long cmd, caddr_t data, struct ifnet *ifp)
                }
 
                rt = nd6_lookup(&nb_addr, 0, ifp, ifp->if_rdomain);
+               mtx_enter(&nd6_mtx);
                if (rt == NULL ||
                    (ln = (struct llinfo_nd6 *)rt->rt_llinfo) == NULL) {
+                       mtx_leave(&nd6_mtx);
                        rtfree(rt);
                        NET_UNLOCK_SHARED();
                        return (EINVAL);
@@ -1006,6 +1012,7 @@ nd6_ioctl(u_long cmd, caddr_t data, struct ifnet *ifp)
                nbi->asked = ln->ln_asked;
                nbi->isrouter = ln->ln_router;
                nbi->expire = expire;
+               mtx_leave(&nd6_mtx);
 
                rtfree(rt);
                NET_UNLOCK_SHARED();
@@ -1035,6 +1042,8 @@ nd6_cache_lladdr(struct ifnet *ifp, const struct in6_addr *from, char *lladdr,
        int llchange;
        int newstate = 0;
 
+       NET_ASSERT_LOCKED_EXCLUSIVE();
+
        if (!ifp)
                panic("%s: ifp == NULL", __func__);
        if (!from)
@@ -1294,23 +1303,20 @@ nd6_resolve(struct ifnet *ifp, struct rtentry *rt0, struct mbuf *m,
                goto bad;
        }
 
-       KERNEL_LOCK();
-       if (!ISSET(rt->rt_flags, RTF_LLINFO)) {
-               KERNEL_UNLOCK();
+       mtx_enter(&nd6_mtx);
+       ln = (struct llinfo_nd6 *)rt->rt_llinfo;
+       if (ln == NULL) {
+               mtx_leave(&nd6_mtx);
                goto bad;
        }
-       ln = (struct llinfo_nd6 *)rt->rt_llinfo;
-       KASSERT(ln != NULL);
 
        /*
         * Move this entry to the head of the queue so that it is less likely
         * for this entry to be a target of forced garbage collection (see
         * nd6_rtrequest()).
         */
-       mtx_enter(&nd6_mtx);
        TAILQ_REMOVE(&nd6_list, ln, ln_list);
        TAILQ_INSERT_HEAD(&nd6_list, ln, ln_list);
-       mtx_leave(&nd6_mtx);
 
        /*
         * The first time we send a packet to a neighbor whose entry is
@@ -1331,7 +1337,7 @@ nd6_resolve(struct ifnet *ifp, struct rtentry *rt0, struct mbuf *m,
         * send the packet.
         */
        if (ln->ln_state > ND6_LLINFO_INCOMPLETE) {
-               KERNEL_UNLOCK();
+               mtx_leave(&nd6_mtx);
 
                sdl = satosdl(rt->rt_gateway);
                if (sdl->sdl_alen != ETHER_ADDR_LEN) {
@@ -1377,7 +1383,7 @@ nd6_resolve(struct ifnet *ifp, struct rtentry *rt0, struct mbuf *m,
                saddr6 = ln->ln_saddr6;
                solicit = 1;
        }
-       KERNEL_UNLOCK();
+       mtx_leave(&nd6_mtx);
 
        if (solicit)
                nd6_ns_output(ifp, NULL, &satosin6(dst)->sin6_addr, &saddr6, 0);