ip6mr: convert mrt_lock to a spinlock

mrt_lock is only held in write mode, from process context only.

We can switch to a mere spinlock, and avoid blocking BH.

Also, vif_dev_read() is always called under standard rcu_read_lock().

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
index 7381cfdac3e376c97917465918a464bd61643f2a..ec6e1509fc7cdfaf55bc79034f43b6e3ce0434ed 100644 (file)
--- a/net/ipv6/ip6mr.c
+++ b/net/ipv6/ip6mr.c
@@ -62,12 +62,11 @@ struct ip6mr_result {
    Note that the changes are semaphored via rtnl_lock.
  */
 
-static DEFINE_RWLOCK(mrt_lock);
+static DEFINE_SPINLOCK(mrt_lock);
 
 static struct net_device *vif_dev_read(const struct vif_device *vif)
 {
-       return rcu_dereference_check(vif->dev,
-                                    lockdep_is_held(&mrt_lock));
+       return rcu_dereference(vif->dev);
 }
 
 /* Multicast router control variables */
@@ -714,7 +713,7 @@ static int mif6_delete(struct mr_table *mrt, int vifi, int notify,
        call_ip6mr_vif_entry_notifiers(read_pnet(&mrt->net),
                                       FIB_EVENT_VIF_DEL, v, dev,
                                       vifi, mrt->id);
-       write_lock_bh(&mrt_lock);
+       spin_lock(&mrt_lock);
        RCU_INIT_POINTER(v->dev, NULL);
 
 #ifdef CONFIG_IPV6_PIMSM_V2
@@ -733,7 +732,7 @@ static int mif6_delete(struct mr_table *mrt, int vifi, int notify,
                WRITE_ONCE(mrt->maxvif, tmp + 1);
        }
 
-       write_unlock_bh(&mrt_lock);
+       spin_unlock(&mrt_lock);
 
        dev_set_allmulti(dev, -1);
 
@@ -833,7 +832,7 @@ static void ipmr_expire_process(struct timer_list *t)
        spin_unlock(&mfc_unres_lock);
 }
 
-/* Fill oifs list. It is called under write locked mrt_lock. */
+/* Fill oifs list. It is called under locked mrt_lock. */
 
 static void ip6mr_update_thresholds(struct mr_table *mrt,
                                    struct mr_mfc *cache,
@@ -919,7 +918,7 @@ static int mif6_add(struct net *net, struct mr_table *mrt,
                        MIFF_REGISTER);
 
        /* And finish update writing critical data */
-       write_lock_bh(&mrt_lock);
+       spin_lock(&mrt_lock);
        rcu_assign_pointer(v->dev, dev);
        netdev_tracker_alloc(dev, &v->dev_tracker, GFP_ATOMIC);
 #ifdef CONFIG_IPV6_PIMSM_V2
@@ -928,7 +927,7 @@ static int mif6_add(struct net *net, struct mr_table *mrt,
 #endif
        if (vifi + 1 > mrt->maxvif)
                WRITE_ONCE(mrt->maxvif, vifi + 1);
-       write_unlock_bh(&mrt_lock);
+       spin_unlock(&mrt_lock);
        call_ip6mr_vif_entry_notifiers(net, FIB_EVENT_VIF_ADD,
                                       v, dev, vifi, mrt->id);
        return 0;
@@ -1442,12 +1441,12 @@ static int ip6mr_mfc_add(struct net *net, struct mr_table *mrt,
                                    &mfc->mf6cc_mcastgrp.sin6_addr, parent);
        rcu_read_unlock();
        if (c) {
-               write_lock_bh(&mrt_lock);
+               spin_lock(&mrt_lock);
                c->_c.mfc_parent = mfc->mf6cc_parent;
                ip6mr_update_thresholds(mrt, &c->_c, ttls);
                if (!mrtsock)
                        c->_c.mfc_flags |= MFC_STATIC;
-               write_unlock_bh(&mrt_lock);
+               spin_unlock(&mrt_lock);
                call_ip6mr_mfc_entry_notifiers(net, FIB_EVENT_ENTRY_REPLACE,
                                               c, mrt->id);
                mr6_netlink_event(mrt, c, RTM_NEWROUTE);
@@ -1565,7 +1564,7 @@ static int ip6mr_sk_init(struct mr_table *mrt, struct sock *sk)
        struct net *net = sock_net(sk);
 
        rtnl_lock();
-       write_lock_bh(&mrt_lock);
+       spin_lock(&mrt_lock);
        if (rtnl_dereference(mrt->mroute_sk)) {
                err = -EADDRINUSE;
        } else {
@@ -1573,7 +1572,7 @@ static int ip6mr_sk_init(struct mr_table *mrt, struct sock *sk)
                sock_set_flag(sk, SOCK_RCU_FREE);
                atomic_inc(&net->ipv6.devconf_all->mc_forwarding);
        }
-       write_unlock_bh(&mrt_lock);
+       spin_unlock(&mrt_lock);
 
        if (!err)
                inet6_netconf_notify_devconf(net, RTM_NEWNETCONF,
@@ -1603,14 +1602,14 @@ int ip6mr_sk_done(struct sock *sk)
        rtnl_lock();
        ip6mr_for_each_table(mrt, net) {
                if (sk == rtnl_dereference(mrt->mroute_sk)) {
-                       write_lock_bh(&mrt_lock);
+                       spin_lock(&mrt_lock);
                        RCU_INIT_POINTER(mrt->mroute_sk, NULL);
                        /* Note that mroute_sk had SOCK_RCU_FREE set,
                         * so the RCU grace period before sk freeing
                         * is guaranteed by sk_destruct()
                         */
                        atomic_dec(&devconf->mc_forwarding);
-                       write_unlock_bh(&mrt_lock);
+                       spin_unlock(&mrt_lock);
                        inet6_netconf_notify_devconf(net, RTM_NEWNETCONF,
                                                     NETCONFA_MC_FORWARDING,
                                                     NETCONFA_IFINDEX_ALL,
@@ -2097,7 +2096,7 @@ out_free:
        return 0;
 }
 
-/* Called with mrt_lock or rcu_read_lock() */
+/* Called with rcu_read_lock() */
 static int ip6mr_find_vif(struct mr_table *mrt, struct net_device *dev)
 {
        int ct;