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    SubjectRe: [PATCH v2] rcu: fix a race in hlist_nulls_for_each_entry_rcu macro
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    Date
    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;





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