llc: convert the socket list to RCU locking

For the reclamation phase we use the SLAB_DESTROY_BY_RCU mechanism,
which require some extra checks in the lookup code:

a) If the current socket was released, reallocated & inserted in
another list it will short circuit the iteration for the current list,
thus we need to restart the lookup.

b) If the current socket was released, reallocated & inserted in the
same list we just need to recheck it matches the look-up criteria and
if not we can skip to the next element.

In this case there is no need to restart the lookup, since sockets are
inserted at the start of the list and the worst that will happen is
that we will iterate throught some of the list elements more then
once.

Note that the /proc and multicast delivery was not yet converted to
RCU, it still uses spinlocks for protection.

Signed-off-by: Octavian Purdila <opurdila@ixiacom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 43 insertions, 23 deletions

diff --git a/net/llc/llc_sap.c b/net/llc/llc_sap.c
index 008de1fc42ca..39760d013ce2 100644
--- a/net/llc/llc_sap.c
+++ b/net/llc/llc_sap.c
@@ -297,6 +297,17 @@ static void llc_sap_rcv(struct llc_sap *sap, struct sk_buff *skb,
         llc_sap_state_process(sap, skb);
 }
 
+static inline bool llc_dgram_match(const struct llc_sap *sap,
+                                   const struct llc_addr *laddr,
+                                   const struct sock *sk)
+{
+     struct llc_sock *llc = llc_sk(sk);
+
+     return sk->sk_type == SOCK_DGRAM &&
+          llc->laddr.lsap == laddr->lsap &&
+          llc_mac_match(llc->laddr.mac, laddr->mac);
+}
+
 /**
  *      llc_lookup_dgram - Finds dgram socket for the local sap/mac
  *      @sap: SAP
@@ -309,25 +320,41 @@ static struct sock *llc_lookup_dgram(struct llc_sap *sap,
                                      const struct llc_addr *laddr)
 {
         struct sock *rc;
-        struct hlist_node *node;
-
-        read_lock_bh(&sap->sk_list.lock);
-        sk_for_each(rc, node, &sap->sk_list.list) {
-                struct llc_sock *llc = llc_sk(rc);
-
-                if (rc->sk_type == SOCK_DGRAM &&
-                    llc->laddr.lsap == laddr->lsap &&
-                    llc_mac_match(llc->laddr.mac, laddr->mac)) {
-                        sock_hold(rc);
+        struct hlist_nulls_node *node;
+
+        rcu_read_lock_bh();
+again:
+        sk_nulls_for_each_rcu(rc, node, &sap->sk_list) {
+                if (llc_dgram_match(sap, laddr, rc)) {
+                        /* Extra checks required by SLAB_DESTROY_BY_RCU */
+                        if (unlikely(!atomic_inc_not_zero(&rc->sk_refcnt)))
+                                goto again;
+                        if (unlikely(llc_sk(rc)->sap != sap ||
+                                     !llc_dgram_match(sap, laddr, rc))) {
+                                sock_put(rc);
+                                continue;
+                        }
                         goto found;
                 }
         }
         rc = NULL;
 found:
-        read_unlock_bh(&sap->sk_list.lock);
+        rcu_read_unlock_bh();
         return rc;
 }
 
+static inline bool llc_mcast_match(const struct llc_sap *sap,
+                                   const struct llc_addr *laddr,
+                                   const struct sk_buff *skb,
+                                   const struct sock *sk)
+{
+     struct llc_sock *llc = llc_sk(sk);
+
+     return sk->sk_type == SOCK_DGRAM &&
+          llc->laddr.lsap == laddr->lsap &&
+          llc->dev == skb->dev;
+}
+
 /**
  *      llc_sap_mcast - Deliver multicast PDU's to all matching datagram sockets.
  *      @sap: SAP
@@ -341,20 +368,13 @@ static void llc_sap_mcast(struct llc_sap *sap,
                           struct sk_buff *skb)
 {
         struct sock *sk;
-        struct hlist_node *node;
+        struct hlist_nulls_node *node;
 
-        read_lock_bh(&sap->sk_list.lock);
-        sk_for_each(sk, node, &sap->sk_list.list) {
-                struct llc_sock *llc = llc_sk(sk);
+        spin_lock_bh(&sap->sk_lock);
+        sk_nulls_for_each_rcu(sk, node, &sap->sk_list) {
                 struct sk_buff *skb1;
 
-                if (sk->sk_type != SOCK_DGRAM)
-                        continue;
-
-                if (llc->laddr.lsap != laddr->lsap)
-                        continue;
-
-                if (llc->dev != skb->dev)
+                if (!llc_mcast_match(sap, laddr, skb, sk))
                         continue;
 
                 skb1 = skb_clone(skb, GFP_ATOMIC);
@@ -365,7 +385,7 @@ static void llc_sap_mcast(struct llc_sap *sap,
                 llc_sap_rcv(sap, skb1, sk);
                 sock_put(sk);
         }
-        read_unlock_bh(&sap->sk_list.lock);
+        spin_unlock_bh(&sap->sk_lock);
 }