udp_notify() invalidates the routing cache without a write lock

[Ryan Stone]

Recently at work I had a system crash while executing RTFREE() in
udp_notify().  In looking at the system I discovered that two threads
had called udp_notify() on the same pcb.  This was possible because
the threads only held a read lock on the socket.  The obvious solution
is to hold a write lock in this path.  I haven't even compile-tested
the patch below yet, but would anybody have any objections to this
approach?

diff --git a/sys/netinet/udp_usrreq.c b/sys/netinet/udp_usrreq.c
index cae044c066c3..429f195ee954 100644
--- a/sys/netinet/udp_usrreq.c
+++ b/sys/netinet/udp_usrreq.c
@@ -756,13 +756,7 @@ struct inpcb *
udp_notify(struct inpcb *inp, int errno)
{

-       /*
-        * While udp_ctlinput() always calls udp_notify() with a read lock
-        * when invoking it directly, in_pcbnotifyall() currently uses write
-        * locks due to sharing code with TCP.  For now, accept either a read
-        * or a write lock, but a read lock is sufficient.
-        */
-       INP_LOCK_ASSERT(inp);
+       INP_WLOCK_ASSERT(inp);
       if ((errno == EHOSTUNREACH || errno == ENETUNREACH ||
            errno == EHOSTDOWN) && inp->inp_route.ro_rt) {
               RTFREE(inp->inp_route.ro_rt);
@@ -808,13 +802,13 @@ udp_common_ctlinput(int cmd, struct sockaddr
*sa, void *vip,
       if (ip != NULL) {
               uh = (struct udphdr *)((caddr_t)ip + (ip->ip_hl << 2));
               inp = in_pcblookup(pcbinfo, faddr, uh->uh_dport,
-                   ip->ip_src, uh->uh_sport, INPLOOKUP_RLOCKPCB, NULL);
+                   ip->ip_src, uh->uh_sport, INPLOOKUP_WLOCKPCB, NULL);
               if (inp != NULL) {
-                       INP_RLOCK_ASSERT(inp);
+                       INP_WLOCK_ASSERT(inp);
                       if (inp->inp_socket != NULL) {
                               udp_notify(inp, inetctlerrmap[cmd]);
                       }
-                       INP_RUNLOCK(inp);
+                       INP_WUNLOCK(inp);
               } else {
                       inp = in_pcblookup(pcbinfo, faddr, uh->uh_dport,
                                          ip->ip_src, uh->uh_sport,