ipvs: add READ_ONCE barrier for ipvs->sysctl_amemthresh

Cc: Julian Anastasov <[email protected]>
Cc: Simon Horman <[email protected]>
Cc: Pablo Neira Ayuso <[email protected]>
Cc: Jozsef Kadlecsik <[email protected]>
Cc: Florian Westphal <[email protected]>
Suggested-by: Julian Anastasov <[email protected]>
Signed-off-by: Alexander Mikhalitsyn <[email protected]>
Acked-by: Julian Anastasov <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: mihalicyn

net/netfilter/ipvs/ip_vs_ctl.c

@@ -94,6 +94,7 @@ static void update_defense_level(struct netns_ipvs *ipvs)
 {
 	struct sysinfo i;
 	int availmem;
+	int amemthresh;
 	int nomem;
 	int to_change = -1;
 
@@ -105,7 +106,8 @@ static void update_defense_level(struct netns_ipvs *ipvs)
 	/* si_swapinfo(&i); */
 	/* availmem = availmem - (i.totalswap - i.freeswap); */
 
-	nomem = (availmem < ipvs->sysctl_amemthresh);
+	amemthresh = max(READ_ONCE(ipvs->sysctl_amemthresh), 0);
+	nomem = (availmem < amemthresh);
 
 	local_bh_disable();
 
@@ -145,19 +147,17 @@ static void update_defense_level(struct netns_ipvs *ipvs)
 		break;
 	case 1:
 		if (nomem) {
-			ipvs->drop_rate = ipvs->drop_counter
-				= ipvs->sysctl_amemthresh /
-				(ipvs->sysctl_amemthresh-availmem);
+			ipvs->drop_counter = amemthresh / (amemthresh - availmem);
+			ipvs->drop_rate = ipvs->drop_counter;
 			ipvs->sysctl_drop_packet = 2;
 		} else {
 			ipvs->drop_rate = 0;
 		}
 		break;
 	case 2:
 		if (nomem) {
-			ipvs->drop_rate = ipvs->drop_counter
-				= ipvs->sysctl_amemthresh /
-				(ipvs->sysctl_amemthresh-availmem);
+			ipvs->drop_counter = amemthresh / (amemthresh - availmem);
+			ipvs->drop_rate = ipvs->drop_counter;
 		} else {
 			ipvs->drop_rate = 0;
 			ipvs->sysctl_drop_packet = 1;