Exclusive net lock or mutex arp_mtx protect the llinfo_arp fields.

So kernel lock is only needed for changing the route rt_flags.  In
arpresolve() protect rt_llinfo lookup and llinfo_arp modification
with arp_mtx.  Grab kernel lock for rt_flags reject modification
only when needed.
Tested by Hrvoje Popovski; OK patrick@ kn@

diff --git a/sys/netinet/if_ether.c b/sys/netinet/if_ether.c
index 69fc0c7..4ecf82f 100644 (file)
--- a/sys/netinet/if_ether.c
+++ b/sys/netinet/if_ether.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: if_ether.c,v 1.262 2023/04/12 16:14:42 kn Exp $       */
+/*     $OpenBSD: if_ether.c,v 1.263 2023/04/25 16:24:25 bluhm Exp $    */
 /*     $NetBSD: if_ether.c,v 1.31 1996/05/11 12:59:58 mycroft Exp $    */
 
 /*
@@ -339,7 +339,7 @@ arpresolve(struct ifnet *ifp, struct rtentry *rt0, struct mbuf *m,
        struct rtentry *rt = NULL;
        char addr[INET_ADDRSTRLEN];
        time_t uptime;
-       int refresh = 0;
+       int refresh = 0, reject = 0;
 
        if (m->m_flags & M_BCAST) {     /* broadcast */
                memcpy(desten, etherbroadcastaddr, sizeof(etherbroadcastaddr));
@@ -411,16 +411,9 @@ arpresolve(struct ifnet *ifp, struct rtentry *rt0, struct mbuf *m,
        if (ifp->if_flags & (IFF_NOARP|IFF_STATICARP))
                goto bad;
 
-       KERNEL_LOCK();
-       /*
-        * Re-check since we grab the kernel lock after the first check.
-        * rtrequest_delete() can be called with shared netlock.  From
-        * there arp_rtrequest() is reached which touches RTF_LLINFO
-        * and rt_llinfo.  As this is called with kernel lock we grab the
-        * kernel lock here and are safe.  XXXSMP
-        */
+       mtx_enter(&arp_mtx);
        if (!ISSET(rt->rt_flags, RTF_LLINFO)) {
-               KERNEL_UNLOCK();
+               mtx_leave(&arp_mtx);
                goto bad;
        }
        la = (struct llinfo_arp *)rt->rt_llinfo;
@@ -451,13 +444,13 @@ arpresolve(struct ifnet *ifp, struct rtentry *rt0, struct mbuf *m,
        }
 #endif
        if (rt->rt_expire) {
-               rt->rt_flags &= ~RTF_REJECT;
+               reject = ~RTF_REJECT;
                if (la->la_asked == 0 || rt->rt_expire != uptime) {
                        rt->rt_expire = uptime;
                        if (la->la_asked++ < arp_maxtries)
                                refresh = 1;
                        else {
-                               rt->rt_flags |= RTF_REJECT;
+                               reject = RTF_REJECT;
                                rt->rt_expire += arpt_down;
                                la->la_asked = 0;
                                la->la_refreshed = 0;
@@ -466,8 +459,18 @@ arpresolve(struct ifnet *ifp, struct rtentry *rt0, struct mbuf *m,
                        }
                }
        }
+       mtx_leave(&arp_mtx);
 
-       KERNEL_UNLOCK();
+       if (reject == RTF_REJECT && !ISSET(rt->rt_flags, RTF_REJECT)) {
+               KERNEL_LOCK();
+               SET(rt->rt_flags, RTF_REJECT);
+               KERNEL_UNLOCK();
+       }
+       if (reject == ~RTF_REJECT && ISSET(rt->rt_flags, RTF_REJECT)) {
+               KERNEL_LOCK();
+               CLR(rt->rt_flags, RTF_REJECT);
+               KERNEL_UNLOCK();
+       }
        if (refresh)
                arprequest(ifp, &satosin(rt->rt_ifa->ifa_addr)->sin_addr.s_addr,
                    &satosin(dst)->sin_addr.s_addr, ac->ac_enaddr);