datapath: Fix deadlock on STT device destroy.

STT unregisters nf-hook when there are no other STT devices
left in the namespace. On some kernel versions the nf-unreg API
take RTNL lock, but it is already taken in the tunnel device
destroy code path which results in deadlock. To fix the issue
I moved the unreg call into net-exit.

VMware-BZ: #1582410
Reported-by: Joe Stringer <joe@ovn.org>
Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Acked-by: Joe Stringer <joe@ovn.org>

diff --git a/datapath/linux/compat/stt.c b/datapath/linux/compat/stt.c
index 85ddbe7..98d6d5b 100644 (file)
--- a/datapath/linux/compat/stt.c
+++ b/datapath/linux/compat/stt.c
@@ -1586,12 +1586,6 @@ static void stt_cleanup(struct net *net)
        sn->n_tunnels--;
        if (sn->n_tunnels)
                goto out;
-#ifdef HAVE_NF_REGISTER_NET_HOOK
-       nf_unregister_net_hook(net, &nf_hook_ops);
-#else
-       nf_unregister_hook(&nf_hook_ops);
-#endif
-
 out:
        n_tunnels--;
        if (n_tunnels)
@@ -1668,6 +1662,7 @@ static int stt_stop(struct net_device *dev)
        struct net *net = stt_dev->net;
 
        list_del_rcu(&stt_dev->up_next);
+       synchronize_net();
        tcp_sock_release(stt_dev->sock);
        stt_dev->sock = NULL;
        stt_cleanup(net);
@@ -1869,6 +1864,14 @@ static void stt_exit_net(struct net *net)
        struct net_device *dev, *aux;
        LIST_HEAD(list);
 
+#ifdef HAVE_NF_REGISTER_NET_HOOK
+       /* Ideally this should be done from stt_stop(), But on some kernels
+        * nf-unreg operation needs RTNL-lock, which can cause deallock.
+        * So it is done from here. */
+       if (!list_empty(&nf_hook_ops.list))
+               nf_unregister_net_hook(net, &nf_hook_ops);
+#endif
+
        rtnl_lock();
 
        /* gather any stt devices that were moved into this ns */
@@ -1908,6 +1911,7 @@ int stt_init_module(void)
        if (rc)
                goto out2;
 
+       INIT_LIST_HEAD(&nf_hook_ops.list);
        pr_info("STT tunneling driver\n");
        return 0;
 out2:
@@ -1918,6 +1922,10 @@ out1:
 
 void stt_cleanup_module(void)
 {
+#ifndef HAVE_NF_REGISTER_NET_HOOK
+       if (!list_empty(&nf_hook_ops.list))
+               nf_unregister_hook(&nf_hook_ops);
+#endif
        rtnl_link_unregister(&stt_link_ops);
        unregister_pernet_subsys(&stt_net_ops);
 }