netns: use a spin_lock to protect nsid management

Before this patch, nsid were protected by the rtnl lock. The goal of this
patch is to be able to find a nsid without needing to hold the rtnl lock.

The next patch will introduce a netlink socket option to listen to all
netns that have a nsid assigned into the netns where the socket is opened.
Thus, it's important to call rtnl_net_notifyid() outside the spinlock, to
avoid a recursive lock (nsid are notified via rtnl). This was the main
reason of the previous patch.

Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index ee86424..ae5008b 100644 (file)
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -28,6 +28,7 @@
 static LIST_HEAD(pernet_list);
 static struct list_head *first_device = &pernet_list;
 DEFINE_MUTEX(net_mutex);
+static DEFINE_SPINLOCK(nsid_lock);
 
 LIST_HEAD(net_namespace_list);
 EXPORT_SYMBOL_GPL(net_namespace_list);
@@ -147,18 +148,17 @@ static void ops_free_list(const struct pernet_operations *ops,
        }
 }
 
+/* should be called with nsid_lock held */
 static int alloc_netid(struct net *net, struct net *peer, int reqid)
 {
        int min = 0, max = 0;
 
-       ASSERT_RTNL();
-
        if (reqid >= 0) {
                min = reqid;
                max = reqid + 1;
        }
 
-       return idr_alloc(&net->netns_ids, peer, min, max, GFP_KERNEL);
+       return idr_alloc(&net->netns_ids, peer, min, max, GFP_ATOMIC);
 }
 
 /* This function is used by idr_for_each(). If net is equal to peer, the
@@ -174,13 +174,15 @@ static int net_eq_idr(int id, void *net, void *peer)
        return 0;
 }
 
+/* Should be called with nsid_lock held. If a new id is assigned, the bool alloc
+ * is set to true, thus the caller knows that the new id must be notified via
+ * rtnl.
+ */
 static int __peernet2id_alloc(struct net *net, struct net *peer, bool *alloc)
 {
        int id = idr_for_each(&net->netns_ids, net_eq_idr, peer);
        bool alloc_it = *alloc;
 
-       ASSERT_RTNL();
-
        *alloc = false;
 
        /* Magic value for id 0. */
@@ -198,6 +200,7 @@ static int __peernet2id_alloc(struct net *net, struct net *peer, bool *alloc)
        return NETNSA_NSID_NOT_ASSIGNED;
 }
 
+/* should be called with nsid_lock held */
 static int __peernet2id(struct net *net, struct net *peer)
 {
        bool no = false;
@@ -211,27 +214,46 @@ static void rtnl_net_notifyid(struct net *net, int cmd, int id);
  */
 int peernet2id_alloc(struct net *net, struct net *peer)
 {
-       bool alloc = atomic_read(&peer->count) == 0 ? false : true;
+       unsigned long flags;
+       bool alloc;
        int id;
 
+       spin_lock_irqsave(&nsid_lock, flags);
+       alloc = atomic_read(&peer->count) == 0 ? false : true;
        id = __peernet2id_alloc(net, peer, &alloc);
+       spin_unlock_irqrestore(&nsid_lock, flags);
        if (alloc && id >= 0)
                rtnl_net_notifyid(net, RTM_NEWNSID, id);
        return id;
 }
 EXPORT_SYMBOL(peernet2id_alloc);
 
+/* This function returns, if assigned, the id of a peer netns. */
+static int peernet2id(struct net *net, struct net *peer)
+{
+       unsigned long flags;
+       int id;
+
+       spin_lock_irqsave(&nsid_lock, flags);
+       id = __peernet2id(net, peer);
+       spin_unlock_irqrestore(&nsid_lock, flags);
+       return id;
+}
+
 struct net *get_net_ns_by_id(struct net *net, int id)
 {
+       unsigned long flags;
        struct net *peer;
 
        if (id < 0)
                return NULL;
 
        rcu_read_lock();
+       spin_lock_irqsave(&nsid_lock, flags);
        peer = idr_find(&net->netns_ids, id);
        if (peer)
                get_net(peer);
+       spin_unlock_irqrestore(&nsid_lock, flags);
        rcu_read_unlock();
 
        return peer;
@@ -372,14 +394,19 @@ static void cleanup_net(struct work_struct *work)
                list_del_rcu(&net->list);
                list_add_tail(&net->exit_list, &net_exit_list);
                for_each_net(tmp) {
-                       int id = __peernet2id(tmp, net);
+                       int id;
 
-                       if (id >= 0) {
-                               rtnl_net_notifyid(tmp, RTM_DELNSID, id);
+                       spin_lock_irq(&nsid_lock);
+                       id = __peernet2id(tmp, net);
+                       if (id >= 0)
                                idr_remove(&tmp->netns_ids, id);
-                       }
+                       spin_unlock_irq(&nsid_lock);
+                       if (id >= 0)
+                               rtnl_net_notifyid(tmp, RTM_DELNSID, id);
                }
+               spin_lock_irq(&nsid_lock);
                idr_destroy(&net->netns_ids);
+               spin_unlock_irq(&nsid_lock);
 
        }
        rtnl_unlock();
@@ -507,6 +534,7 @@ static int rtnl_net_newid(struct sk_buff *skb, struct nlmsghdr *nlh)
 {
        struct net *net = sock_net(skb->sk);
        struct nlattr *tb[NETNSA_MAX + 1];
+       unsigned long flags;
        struct net *peer;
        int nsid, err;
 
@@ -527,12 +555,14 @@ static int rtnl_net_newid(struct sk_buff *skb, struct nlmsghdr *nlh)
        if (IS_ERR(peer))
                return PTR_ERR(peer);
 
+       spin_lock_irqsave(&nsid_lock, flags);
        if (__peernet2id(net, peer) >= 0) {
                err = -EEXIST;
                goto out;
        }
 
        err = alloc_netid(net, peer, nsid);
+       spin_unlock_irqrestore(&nsid_lock, flags);
        if (err >= 0) {
                rtnl_net_notifyid(net, RTM_NEWNSID, err);
                err = 0;
@@ -601,7 +631,7 @@ static int rtnl_net_getid(struct sk_buff *skb, struct nlmsghdr *nlh)
                goto out;
        }
 
-       id = __peernet2id(net, peer);
+       id = peernet2id(net, peer);
        err = rtnl_net_fill(msg, NETLINK_CB(skb).portid, nlh->nlmsg_seq, 0,
                            RTM_GETNSID, net, id);
        if (err < 0)
@@ -654,10 +684,11 @@ static int rtnl_net_dumpid(struct sk_buff *skb, struct netlink_callback *cb)
                .idx = 0,
                .s_idx = cb->args[0],
        };
+       unsigned long flags;
 
-       ASSERT_RTNL();
-
+       spin_lock_irqsave(&nsid_lock, flags);
        idr_for_each(&net->netns_ids, rtnl_net_dumpid_one, &net_cb);
+       spin_unlock_irqrestore(&nsid_lock, flags);
 
        cb->args[0] = net_cb.idx;
        return skb->len;