[RFC] packet: change call of synchronize_net to call_rcu

Signed-off-by: Sorin Dumitru <redacted>
Signed-off-by: Iulius Curt <redacted>
---
Statistics using test program [1]

Sockets count  |  Not patched  |  Patched
_________________________________________
    1 000 000  |       1.28 s  |   1.22 s
    5 000 000  |        7.3 s  |   6.25 s
   50 000 000  |      72.89 s  |  64.41 s

[1] http://pastebin.com/xQ9BziaP
---
 net/packet/af_packet.c |   46 ++++++++++++++++++++++++++++++++++++----------
 net/packet/internal.h  |    1 +
 2 files changed, 37 insertions(+), 10 deletions(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 5dafe84..7b60135 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c

@@ -2299,6 +2299,32 @@ static int packet_sendmsg(struct kiocb *iocb, struct socket *sock,
                return packet_snd(sock, msg, len);
 }

+void packet_release_finish(struct sock *sk, int null)
+{
+       struct socket *sock = sk->sk_socket;
+
+       sock_orphan(sk);
+       /* Modifing this after the socket has been released
+        * might lead to memory corruption so we don't do it */
+       if (null)
+               sock->sk = NULL;

+       /* Purge queues */
+
+       skb_queue_purge(&sk->sk_receive_queue);
+       sk_refcnt_debug_release(sk);
+
+       sock_put(sk);
+}
+
+void packet_release_rcu(struct rcu_head *rcu)
+{
+       struct packet_sock *po = container_of(rcu, struct packet_sock, rcu_head);
+       struct sock *sk = &po->sk;
+
+       packet_release_finish(sk, 0);
+}
+
 /*
  *     Close a PACKET socket. This is fairly simple. We immediately go
  *     to 'closed' state and remove our protocol entry in the device list.

@@ -2310,6 +2336,7 @@ static int packet_release(struct socket *sock)
        struct packet_sock *po;
        struct net *net;
        union tpacket_req_u req_u;
+       int postpone = 0;

        if (!sk)
                return 0;

@@ -2326,7 +2353,10 @@ static int packet_release(struct socket *sock)
        preempt_enable();

        spin_lock(&po->bind_lock);
-       unregister_prot_hook(sk, false);
+       if (po->running) {
+               postpone = 1;
+               __unregister_prot_hook(sk, false);
+       }
        if (po->prot_hook.dev) {
                dev_put(po->prot_hook.dev);
                po->prot_hook.dev = NULL;

@@ -2345,19 +2375,15 @@ static int packet_release(struct socket *sock)

        fanout_release(sk);

-       synchronize_net();
        /*
         *      Now the socket is dead. No more input will appear.
         */
-       sock_orphan(sk);
-       sock->sk = NULL;
-
-       /* Purge queues */
-
-       skb_queue_purge(&sk->sk_receive_queue);
-       sk_refcnt_debug_release(sk);
+       if (postpone) {
+               call_rcu(&po->rcu_head, packet_release_rcu);
+               return 0;
+       }

-       sock_put(sk);
+       packet_release_finish(sk, 1);
        return 0;
 }

diff --git a/net/packet/internal.h b/net/packet/internal.h
index 44945f6..5778c12 100644
--- a/net/packet/internal.h
+++ b/net/packet/internal.h

@@ -104,6 +104,7 @@ struct packet_sock {
        int                     ifindex;        /* bound device         */
        __be16                  num;
        struct packet_mclist    *mclist;
+       struct rcu_head         rcu_head;
        atomic_t                mapped;
        enum tpacket_versions   tp_version;
        unsigned int            tp_hdrlen;
--

1.7.9.5