[PATCH] 2.5.68 - RCU for SNAP

[Stephen Hemminger <shemminger@xxxxxxxx>]

Replace br_lock() in snap with Read Copy Update.

Straightforward since SNAP uses list macros already.

Tested by bringing up/down Appletalk on SMP system and making sure packets
get through.

This is the last subsystem that depends on br_lock before IPV4,IPV6
can be converted.

--- linux-2.5/net/802/psnap.c   2003-04-14 13:32:25.000000000 -0700
+++ linux-2.5-bridge/net/802/psnap.c    2003-04-29 15:42:04.000000000 -0700
@@ -21,9 +21,9 @@
 #include <linux/mm.h>
 #include <linux/in.h>
 #include <linux/init.h>
-#include <linux/brlock.h>
 
-LIST_HEAD(snap_list);
+static LIST_HEAD(snap_list);
+static spinlock_t snap_lock = SPIN_LOCK_UNLOCKED;
 static struct llc_sap *snap_sap;
 
 /*
@@ -34,17 +34,13 @@
        struct list_head *entry;
        struct datalink_proto *proto = NULL, *p;
 
-       if (list_empty(&snap_list))
-               goto out;
-
-       list_for_each(entry, &snap_list) {
+       list_for_each_rcu(entry, &snap_list) {
                p = list_entry(entry, struct datalink_proto, node);
                if (!memcmp(p->type, desc, 5)) {
                        proto = p;
                        break;
                }
        }
-out:
        return proto;
 }
 
@@ -55,11 +51,13 @@
                    struct packet_type *pt)
 {
        int rc = 1;
-       struct datalink_proto *proto = find_snap_client(skb->h.raw);
+       struct datalink_proto *proto;
        static struct packet_type snap_packet_type = {
                .type = __constant_htons(ETH_P_SNAP),
        };
 
+       rcu_read_lock();
+       proto = find_snap_client(skb->h.raw);
        if (proto) {
                /* Pass the frame on. */
                skb->h.raw  += 5;
@@ -71,6 +69,7 @@
                rc = 1;
        }
 
+       rcu_read_unlock();
        return rc;
 }
 
@@ -124,7 +123,7 @@
 {
        struct datalink_proto *proto = NULL;
 
-       br_write_lock_bh(BR_NETPROTO_LOCK);
+       spin_lock_bh(&snap_lock);
 
        if (find_snap_client(desc))
                goto out;
@@ -135,10 +134,12 @@
                proto->rcvfunc          = rcvfunc;
                proto->header_length    = 5 + 3; /* snap + 802.2 */
                proto->request          = snap_request;
-               list_add(&proto->node, &snap_list);
+               list_add_rcu(&proto->node, &snap_list);
        }
 out:
-       br_write_unlock_bh(BR_NETPROTO_LOCK);
+       spin_unlock_bh(&snap_lock);
+
+       synchronize_net();
        return proto;
 }
 
@@ -147,12 +148,13 @@
  */
 void unregister_snap_client(struct datalink_proto *proto)
 {
-       br_write_lock_bh(BR_NETPROTO_LOCK);
+       spin_lock_bh(&snap_lock);
+       list_del_rcu(&proto->node);
+       spin_unlock_bh(&snap_lock);
 
-       list_del(&proto->node);
-       kfree(proto);
+       synchronize_net();
 
-       br_write_unlock_bh(BR_NETPROTO_LOCK);
+       kfree(proto);
 }
 
 MODULE_LICENSE("GPL");