mptcp: refactor token container

Replace the radix tree with a hash table allocated
at boot time. The radix tree has some shortcoming:
a single lock is contented by all the mptcp operation,
the lookup currently use such lock, and traversing
all the items would require a lock, too.

With hash table instead we trade a little memory to
address all the above - a per bucket lock is used.

To hash the MPTCP sockets, we re-use the msk' sk_node
entry: the MPTCP sockets are never hashed by the stack.
Replace the existing hash proto callbacks with a dummy
implementation, annotating the above constraint.

Additionally refactor the token creation to code to:

- limit the number of consecutive attempts to a fixed
maximum. Hitting a hash bucket with a long chain is
considered a failed attempt

- accept() no longer can fail to token management.

- if token creation fails at connect() time, we do
fallback to TCP (before the connection was closed)

v1 -> v2:
 - fix "no newline at end of file" - Jakub

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 192 insertions, 79 deletions

diff --git a/net/mptcp/token.c b/net/mptcp/token.c
index 33352dd99d4d..9c0771774815 100644
--- a/net/mptcp/token.c
+++ b/net/mptcp/token.c
@@ -24,7 +24,7 @@
 
 #include <linux/kernel.h>
 #include <linux/module.h>
-#include <linux/radix-tree.h>
+#include <linux/memblock.h>
 #include <linux/ip.h>
 #include <linux/tcp.h>
 #include <net/sock.h>
@@ -33,10 +33,55 @@
 #include <net/mptcp.h>
 #include "protocol.h"
 
-static RADIX_TREE(token_tree, GFP_ATOMIC);
-static RADIX_TREE(token_req_tree, GFP_ATOMIC);
-static DEFINE_SPINLOCK(token_tree_lock);
-static int token_used __read_mostly;
+#define TOKEN_MAX_RETRIES	4
+#define TOKEN_MAX_CHAIN_LEN	4
+
+struct token_bucket {
+	spinlock_t		lock;
+	int			chain_len;
+	struct hlist_nulls_head	req_chain;
+	struct hlist_nulls_head	msk_chain;
+};
+
+static struct token_bucket *token_hash __read_mostly;
+static unsigned int token_mask __read_mostly;
+
+static struct token_bucket *token_bucket(u32 token)
+{
+	return &token_hash[token & token_mask];
+}
+
+/* called with bucket lock held */
+static struct mptcp_subflow_request_sock *
+__token_lookup_req(struct token_bucket *t, u32 token)
+{
+	struct mptcp_subflow_request_sock *req;
+	struct hlist_nulls_node *pos;
+
+	hlist_nulls_for_each_entry_rcu(req, pos, &t->req_chain, token_node)
+		if (req->token == token)
+			return req;
+	return NULL;
+}
+
+/* called with bucket lock held */
+static struct mptcp_sock *
+__token_lookup_msk(struct token_bucket *t, u32 token)
+{
+	struct hlist_nulls_node *pos;
+	struct sock *sk;
+
+	sk_nulls_for_each_rcu(sk, pos, &t->msk_chain)
+		if (mptcp_sk(sk)->token == token)
+			return mptcp_sk(sk);
+	return NULL;
+}
+
+static bool __token_bucket_busy(struct token_bucket *t, u32 token)
+{
+	return !token || t->chain_len >= TOKEN_MAX_CHAIN_LEN ||
+	       __token_lookup_req(t, token) || __token_lookup_msk(t, token);
+}
 
 /**
  * mptcp_token_new_request - create new key/idsn/token for subflow_request
@@ -52,30 +97,32 @@ static int token_used __read_mostly;
 int mptcp_token_new_request(struct request_sock *req)
 {
 	struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);
-	int err;
-
-	while (1) {
-		u32 token;
-
-		mptcp_crypto_key_gen_sha(&subflow_req->local_key,
-					 &subflow_req->token,
-					 &subflow_req->idsn);
-		pr_debug("req=%p local_key=%llu, token=%u, idsn=%llu\n",
-			 req, subflow_req->local_key, subflow_req->token,
-			 subflow_req->idsn);
-
-		token = subflow_req->token;
-		spin_lock_bh(&token_tree_lock);
-		if (!radix_tree_lookup(&token_req_tree, token) &&
-		    !radix_tree_lookup(&token_tree, token))
-			break;
-		spin_unlock_bh(&token_tree_lock);
+	int retries = TOKEN_MAX_RETRIES;
+	struct token_bucket *bucket;
+	u32 token;
+
+again:
+	mptcp_crypto_key_gen_sha(&subflow_req->local_key,
+				 &subflow_req->token,
+				 &subflow_req->idsn);
+	pr_debug("req=%p local_key=%llu, token=%u, idsn=%llu\n",
+		 req, subflow_req->local_key, subflow_req->token,
+		 subflow_req->idsn);
+
+	token = subflow_req->token;
+	bucket = token_bucket(token);
+	spin_lock_bh(&bucket->lock);
+	if (__token_bucket_busy(bucket, token)) {
+		spin_unlock_bh(&bucket->lock);
+		if (!--retries)
+			return -EBUSY;
+		goto again;
 	}
 
-	err = radix_tree_insert(&token_req_tree,
-				subflow_req->token, &token_used);
-	spin_unlock_bh(&token_tree_lock);
-	return err;
+	hlist_nulls_add_head_rcu(&subflow_req->token_node, &bucket->req_chain);
+	bucket->chain_len++;
+	spin_unlock_bh(&bucket->lock);
+	return 0;
 }
 
 /**
@@ -97,48 +144,56 @@ int mptcp_token_new_request(struct request_sock *req)
 int mptcp_token_new_connect(struct sock *sk)
 {
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
-	struct sock *mptcp_sock = subflow->conn;
-	int err;
-
-	while (1) {
-		u32 token;
+	struct mptcp_sock *msk = mptcp_sk(subflow->conn);
+	int retries = TOKEN_MAX_RETRIES;
+	struct token_bucket *bucket;
 
-		mptcp_crypto_key_gen_sha(&subflow->local_key, &subflow->token,
-					 &subflow->idsn);
+	pr_debug("ssk=%p, local_key=%llu, token=%u, idsn=%llu\n",
+		 sk, subflow->local_key, subflow->token, subflow->idsn);
 
-		pr_debug("ssk=%p, local_key=%llu, token=%u, idsn=%llu\n",
-			 sk, subflow->local_key, subflow->token, subflow->idsn);
+again:
+	mptcp_crypto_key_gen_sha(&subflow->local_key, &subflow->token,
+				 &subflow->idsn);
 
-		token = subflow->token;
-		spin_lock_bh(&token_tree_lock);
-		if (!radix_tree_lookup(&token_req_tree, token) &&
-		    !radix_tree_lookup(&token_tree, token))
-			break;
-		spin_unlock_bh(&token_tree_lock);
+	bucket = token_bucket(subflow->token);
+	spin_lock_bh(&bucket->lock);
+	if (__token_bucket_busy(bucket, subflow->token)) {
+		spin_unlock_bh(&bucket->lock);
+		if (!--retries)
+			return -EBUSY;
+		goto again;
 	}
-	err = radix_tree_insert(&token_tree, subflow->token, mptcp_sock);
-	spin_unlock_bh(&token_tree_lock);
 
-	return err;
+	WRITE_ONCE(msk->token, subflow->token);
+	__sk_nulls_add_node_rcu((struct sock *)msk, &bucket->msk_chain);
+	bucket->chain_len++;
+	spin_unlock_bh(&bucket->lock);
+	return 0;
 }
 
 /**
- * mptcp_token_new_accept - insert token for later processing
- * @token: the token to insert to the tree
- * @conn: the just cloned socket linked to the new connection
+ * mptcp_token_accept - replace a req sk with full sock in token hash
+ * @req: the request socket to be removed
+ * @msk: the just cloned socket linked to the new connection
  *
  * Called when a SYN packet creates a new logical connection, i.e.
  * is not a join request.
  */
-int mptcp_token_new_accept(u32 token, struct sock *conn)
+void mptcp_token_accept(struct mptcp_subflow_request_sock *req,
+			struct mptcp_sock *msk)
 {
-	int err;
+	struct mptcp_subflow_request_sock *pos;
+	struct token_bucket *bucket;
 
-	spin_lock_bh(&token_tree_lock);
-	err = radix_tree_insert(&token_tree, token, conn);
-	spin_unlock_bh(&token_tree_lock);
+	bucket = token_bucket(req->token);
+	spin_lock_bh(&bucket->lock);
 
-	return err;
+	/* pedantic lookup check for the moved token */
+	pos = __token_lookup_req(bucket, req->token);
+	if (!WARN_ON_ONCE(pos != req))
+		hlist_nulls_del_init_rcu(&req->token_node);
+	__sk_nulls_add_node_rcu((struct sock *)msk, &bucket->msk_chain);
+	spin_unlock_bh(&bucket->lock);
 }
 
 /**
@@ -152,45 +207,103 @@ int mptcp_token_new_accept(u32 token, struct sock *conn)
  */
 struct mptcp_sock *mptcp_token_get_sock(u32 token)
 {
-	struct sock *conn;
-
-	spin_lock_bh(&token_tree_lock);
-	conn = radix_tree_lookup(&token_tree, token);
-	if (conn) {
-		/* token still reserved? */
-		if (conn == (struct sock *)&token_used)
-			conn = NULL;
-		else
-			sock_hold(conn);
+	struct hlist_nulls_node *pos;
+	struct token_bucket *bucket;
+	struct mptcp_sock *msk;
+	struct sock *sk;
+
+	rcu_read_lock();
+	bucket = token_bucket(token);
+
+again:
+	sk_nulls_for_each_rcu(sk, pos, &bucket->msk_chain) {
+		msk = mptcp_sk(sk);
+		if (READ_ONCE(msk->token) != token)
+			continue;
+		if (!refcount_inc_not_zero(&sk->sk_refcnt))
+			goto not_found;
+		if (READ_ONCE(msk->token) != token) {
+			sock_put(sk);
+			goto again;
+		}
+		goto found;
 	}
-	spin_unlock_bh(&token_tree_lock);
+	if (get_nulls_value(pos) != (token & token_mask))
+		goto again;
+
+not_found:
+	msk = NULL;
 
-	return mptcp_sk(conn);
+found:
+	rcu_read_unlock();
+	return msk;
 }
 
 /**
  * mptcp_token_destroy_request - remove mptcp connection/token
- * @token: token of mptcp connection to remove
+ * @req: mptcp request socket dropping the token
  *
- * Remove not-yet-fully-established incoming connection identified
- * by @token.
+ * Remove the token associated to @req.
  */
-void mptcp_token_destroy_request(u32 token)
+void mptcp_token_destroy_request(struct request_sock *req)
 {
-	spin_lock_bh(&token_tree_lock);
-	radix_tree_delete(&token_req_tree, token);
-	spin_unlock_bh(&token_tree_lock);
+	struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);
+	struct mptcp_subflow_request_sock *pos;
+	struct token_bucket *bucket;
+
+	if (hlist_nulls_unhashed(&subflow_req->token_node))
+		return;
+
+	bucket = token_bucket(subflow_req->token);
+	spin_lock_bh(&bucket->lock);
+	pos = __token_lookup_req(bucket, subflow_req->token);
+	if (!WARN_ON_ONCE(pos != subflow_req)) {
+		hlist_nulls_del_init_rcu(&pos->token_node);
+		bucket->chain_len--;
+	}
+	spin_unlock_bh(&bucket->lock);
 }
 
 /**
  * mptcp_token_destroy - remove mptcp connection/token
- * @token: token of mptcp connection to remove
+ * @msk: mptcp connection dropping the token
  *
- * Remove the connection identified by @token.
+ * Remove the token associated to @msk
  */
-void mptcp_token_destroy(u32 token)
+void mptcp_token_destroy(struct mptcp_sock *msk)
 {
-	spin_lock_bh(&token_tree_lock);
-	radix_tree_delete(&token_tree, token);
-	spin_unlock_bh(&token_tree_lock);
+	struct token_bucket *bucket;
+	struct mptcp_sock *pos;
+
+	if (sk_unhashed((struct sock *)msk))
+		return;
+
+	bucket = token_bucket(msk->token);
+	spin_lock_bh(&bucket->lock);
+	pos = __token_lookup_msk(bucket, msk->token);
+	if (!WARN_ON_ONCE(pos != msk)) {
+		__sk_nulls_del_node_init_rcu((struct sock *)pos);
+		bucket->chain_len--;
+	}
+	spin_unlock_bh(&bucket->lock);
+}
+
+void __init mptcp_token_init(void)
+{
+	int i;
+
+	token_hash = alloc_large_system_hash("MPTCP token",
+					     sizeof(struct token_bucket),
+					     0,
+					     20,/* one slot per 1MB of memory */
+					     0,
+					     NULL,
+					     &token_mask,
+					     0,
+					     64 * 1024);
+	for (i = 0; i < token_mask + 1; ++i) {
+		INIT_HLIST_NULLS_HEAD(&token_hash[i].req_chain, i);
+		INIT_HLIST_NULLS_HEAD(&token_hash[i].msk_chain, i);
+		spin_lock_init(&token_hash[i].lock);
+	}
 }