Re: [PATCH v2] rcu: fix a race in hlist_nulls_for_each_entry_rcu macro
From: Eric Dumazet <hidden>
Date: 2013-05-22 05:49:29
Also in:
lkml
Subsystem:
networking [general], the rest, user datagram protocol (udp) · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds, Willem de Bruijn
On Tue, 2013-05-21 at 19:01 -0700, Eric Dumazet wrote:
Please use ACCESS_ONCE(), which is the standard way to deal with this, and remove the rcu_dereference_raw() in hlist_nulls_for_each_entry_rcu() something like : (for the nulls part only)
Thinking a bit more about this, I am a bit worried by other uses of ACCESS_ONCE(ptr->field) rcu_dereference(ptr->field) intent is to reload ptr->field every time from memory. Do we really need a #define ACCESS_FIELD_ONCE(PTR, FIELD) (((volatile typeof(*PTR) *)PTR)->FIELD) #define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x)) and change all rcu_dererence(ptr->field) occurrences ? I probably miss something obvious. Anyway, following patch seems to also solve the problem, I need a sleep to understand why.
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 0bf5d39..10b5c54 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c@@ -410,7 +410,7 @@ static inline int compute_score2(struct sock *sk, struct net *net, static struct sock *udp4_lib_lookup2(struct net *net, __be32 saddr, __be16 sport, __be32 daddr, unsigned int hnum, int dif, - struct udp_hslot *hslot2, unsigned int slot2) + struct hlist_nulls_head *head, unsigned int slot2) { struct sock *sk, *result; struct hlist_nulls_node *node;
@@ -420,7 +420,7 @@ static struct sock *udp4_lib_lookup2(struct net *net, begin: result = NULL; badness = 0; - udp_portaddr_for_each_entry_rcu(sk, node, &hslot2->head) { + udp_portaddr_for_each_entry_rcu(sk, node, head) { score = compute_score2(sk, net, saddr, sport, daddr, hnum, dif); if (score > badness) {
@@ -483,7 +483,7 @@ struct sock *__udp4_lib_lookup(struct net *net, __be32 saddr, result = udp4_lib_lookup2(net, saddr, sport, daddr, hnum, dif, - hslot2, slot2); + &hslot2->head, slot2); if (!result) { hash2 = udp4_portaddr_hash(net, htonl(INADDR_ANY), hnum); slot2 = hash2 & udptable->mask;
@@ -493,7 +493,7 @@ struct sock *__udp4_lib_lookup(struct net *net, __be32 saddr, result = udp4_lib_lookup2(net, saddr, sport, htonl(INADDR_ANY), hnum, dif, - hslot2, slot2); + &hslot2->head, slot2); } rcu_read_unlock(); return result;
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 42923b1..b5bc667 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c@@ -200,7 +200,7 @@ static inline int compute_score2(struct sock *sk, struct net *net, static struct sock *udp6_lib_lookup2(struct net *net, const struct in6_addr *saddr, __be16 sport, const struct in6_addr *daddr, unsigned int hnum, int dif, - struct udp_hslot *hslot2, unsigned int slot2) + struct hlist_nulls_head *head, unsigned int slot2) { struct sock *sk, *result; struct hlist_nulls_node *node;
@@ -210,7 +210,7 @@ static struct sock *udp6_lib_lookup2(struct net *net, begin: result = NULL; badness = -1; - udp_portaddr_for_each_entry_rcu(sk, node, &hslot2->head) { + udp_portaddr_for_each_entry_rcu(sk, node, head) { score = compute_score2(sk, net, saddr, sport, daddr, hnum, dif); if (score > badness) {
@@ -274,7 +274,7 @@ struct sock *__udp6_lib_lookup(struct net *net, result = udp6_lib_lookup2(net, saddr, sport, daddr, hnum, dif, - hslot2, slot2); + &hslot2->head, slot2); if (!result) { hash2 = udp6_portaddr_hash(net, &in6addr_any, hnum); slot2 = hash2 & udptable->mask;
@@ -284,7 +284,7 @@ struct sock *__udp6_lib_lookup(struct net *net, result = udp6_lib_lookup2(net, saddr, sport, &in6addr_any, hnum, dif, - hslot2, slot2); + &hslot2->head, slot2); } rcu_read_unlock(); return result;