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, 11 insertions, 3 deletions

diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index 571d39a1a17c..c05552e5fa23 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -250,6 +250,7 @@ struct mptcp_subflow_request_sock {
 	u32	local_nonce;
 	u32	remote_nonce;
 	struct mptcp_sock	*msk;
+	struct hlist_nulls_node token_node;
 };
 
 static inline struct mptcp_subflow_request_sock *
@@ -372,12 +373,19 @@ bool mptcp_finish_join(struct sock *sk);
 void mptcp_data_acked(struct sock *sk);
 void mptcp_subflow_eof(struct sock *sk);
 
+void __init mptcp_token_init(void);
+static inline void mptcp_token_init_request(struct request_sock *req)
+{
+	mptcp_subflow_rsk(req)->token_node.pprev = NULL;
+}
+
 int mptcp_token_new_request(struct request_sock *req);
-void mptcp_token_destroy_request(u32 token);
+void mptcp_token_destroy_request(struct request_sock *req);
 int mptcp_token_new_connect(struct sock *sk);
-int mptcp_token_new_accept(u32 token, struct sock *conn);
+void mptcp_token_accept(struct mptcp_subflow_request_sock *r,
+			struct mptcp_sock *msk);
 struct mptcp_sock *mptcp_token_get_sock(u32 token);
-void mptcp_token_destroy(u32 token);
+void mptcp_token_destroy(struct mptcp_sock *msk);
 
 void mptcp_crypto_key_sha(u64 key, u32 *token, u64 *idsn);
 static inline void mptcp_crypto_key_gen_sha(u64 *key, u32 *token, u64 *idsn)