neigh: support smaller retrans_time settting

Currently, we limited the retrans_time to be greater than HZ/2. i.e.
setting retrans_time less than 500ms will not work. This makes the user
unable to achieve a more accurate control for bonding arp fast failover.

Update the sanity check to HZ/100, which is 10ms, to let users have more
ability on the retrans_time control.

v3: sync the behavior with IPv6 and update all the timer handler
v2: use HZ instead of hard code number
Signed-off-by: NHangbin Liu <liuhangbin@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/neighbour.c

@@ -1065,11 +1065,12 @@ static void neigh_timer_handler(struct timer_list *t)
 			neigh->updated = jiffies;
 			atomic_set(&neigh->probes, 0);
 			notify = 1;
-			next = now + NEIGH_VAR(neigh->parms, RETRANS_TIME);
+			next = now + max(NEIGH_VAR(neigh->parms, RETRANS_TIME),
+					 HZ/100);
 		}
 	} else {
 		/* NUD_PROBE|NUD_INCOMPLETE */
-		next = now + NEIGH_VAR(neigh->parms, RETRANS_TIME);
+		next = now + max(NEIGH_VAR(neigh->parms, RETRANS_TIME), HZ/100);
 	}
 
 	if ((neigh->nud_state & (NUD_INCOMPLETE | NUD_PROBE)) &&
@@ -1125,7 +1126,7 @@ int __neigh_event_send(struct neighbour *neigh, struct sk_buff *skb)
 			neigh->nud_state     = NUD_INCOMPLETE;
 			neigh->updated = now;
 			next = now + max(NEIGH_VAR(neigh->parms, RETRANS_TIME),
-					 HZ/2);
+					 HZ/100);
 			neigh_add_timer(neigh, next);
 			immediate_probe = true;
 		} else {
@@ -1427,7 +1428,8 @@ void __neigh_set_probe_once(struct neighbour *neigh)
 	neigh->nud_state = NUD_INCOMPLETE;
 	atomic_set(&neigh->probes, neigh_max_probes(neigh));
 	neigh_add_timer(neigh,
-			jiffies + NEIGH_VAR(neigh->parms, RETRANS_TIME));
+			jiffies + max(NEIGH_VAR(neigh->parms, RETRANS_TIME),
+				      HZ/100));
 }
 EXPORT_SYMBOL(__neigh_set_probe_once);
 

net/ipv6/addrconf.c

@@ -1357,7 +1357,7 @@ static int ipv6_create_tempaddr(struct inet6_ifaddr *ifp,
 
 	regen_advance = idev->cnf.regen_max_retry *
 			idev->cnf.dad_transmits *
-			NEIGH_VAR(idev->nd_parms, RETRANS_TIME) / HZ;
+			max(NEIGH_VAR(idev->nd_parms, RETRANS_TIME), HZ/100) / HZ;
 
 	/* recalculate max_desync_factor each time and update
 	 * idev->desync_factor if it's larger
@@ -4121,7 +4121,8 @@ static void addrconf_dad_work(struct work_struct *w)
 
 	ifp->dad_probes--;
 	addrconf_mod_dad_work(ifp,
-			      NEIGH_VAR(ifp->idev->nd_parms, RETRANS_TIME));
+			      max(NEIGH_VAR(ifp->idev->nd_parms, RETRANS_TIME),
+				  HZ/100));
 	spin_unlock(&ifp->lock);
 	write_unlock_bh(&idev->lock);
 
@@ -4527,7 +4528,7 @@ static void addrconf_verify_rtnl(void)
 				   !(ifp->flags&IFA_F_TENTATIVE)) {
 				unsigned long regen_advance = ifp->idev->cnf.regen_max_retry *
 					ifp->idev->cnf.dad_transmits *
-					NEIGH_VAR(ifp->idev->nd_parms, RETRANS_TIME) / HZ;
+					max(NEIGH_VAR(ifp->idev->nd_parms, RETRANS_TIME), HZ/100) / HZ;
 
 				if (age >= ifp->prefered_lft - regen_advance) {
 					struct inet6_ifaddr *ifpub = ifp->ifpub;

net/ipv6/ndisc.c

@@ -1359,8 +1359,8 @@ static void ndisc_router_discovery(struct sk_buff *skb)
 
 		if (rtime && rtime/1000 < MAX_SCHEDULE_TIMEOUT/HZ) {
 			rtime = (rtime*HZ)/1000;
-			if (rtime < HZ/10)
-				rtime = HZ/10;
+			if (rtime < HZ/100)
+				rtime = HZ/100;
 			NEIGH_VAR_SET(in6_dev->nd_parms, RETRANS_TIME, rtime);
 			in6_dev->tstamp = jiffies;
 			send_ifinfo_notify = true;