rxrpc: Calls shouldn't hold socket refs

rxrpc calls shouldn't hold refs on the sock struct.  This was done so that
the socket wouldn't go away whilst the call was in progress, such that the
call could reach the socket's queues.

However, we can mark the socket as requiring an RCU release and rely on the
RCU read lock.

To make this work, we do:

 (1) rxrpc_release_call() removes the call's call user ID.  This is now
     only called from socket operations and not from the call processor:

	rxrpc_accept_call() / rxrpc_kernel_accept_call()
	rxrpc_reject_call() / rxrpc_kernel_reject_call()
	rxrpc_kernel_end_call()
	rxrpc_release_calls_on_socket()
	rxrpc_recvmsg()

     Though it is also called in the cleanup path of
     rxrpc_accept_incoming_call() before we assign a user ID.

 (2) Pass the socket pointer into rxrpc_release_call() rather than getting
     it from the call so that we can get rid of uninitialised calls.

 (3) Fix call processor queueing to pass a ref to the work queue and to
     release that ref at the end of the processor function (or to pass it
     back to the work queue if we have to requeue).

 (4) Skip out of the call processor function asap if the call is complete
     and don't requeue it if the call is complete.

 (5) Clean up the call immediately that the refcount reaches 0 rather than
     trying to defer it.  Actual deallocation is deferred to RCU, however.

 (6) Don't hold socket refs for allocated calls.

 (7) Use the RCU read lock when queueing a message on a socket and treat
     the call's socket pointer according to RCU rules and check it for
     NULL.

     We also need to use the RCU read lock when viewing a call through
     procfs.

 (8) Transmit the final ACK/ABORT to a client call in rxrpc_release_call()
     if this hasn't been done yet so that we can then disconnect the call.
     Once the call is disconnected, it won't have any access to the
     connection struct and the UDP socket for the call work processor to be
     able to send the ACK.  Terminal retransmission will be handled by the
     connection processor.

 (9) Release all calls immediately on the closing of a socket rather than
     trying to defer this.  Incomplete calls will be aborted.

The call refcount model is much simplified.  Refs are held on the call by:

 (1) A socket's user ID tree.

 (2) A socket's incoming call secureq and acceptq.

 (3) A kernel service that has a call in progress.

 (4) A queued call work processor.  We have to take care to put any call
     that we failed to queue.

 (5) sk_buffs on a socket's receive queue.  A future patch will get rid of
     this.

Whilst we're at it, we can do:

 (1) Get rid of the RXRPC_CALL_EV_RELEASE event.  Release is now done
     entirely from the socket routines and never from the call's processor.

 (2) Get rid of the RXRPC_CALL_DEAD state.  Calls now end in the
     RXRPC_CALL_COMPLETE state.

 (3) Get rid of the rxrpc_call::destroyer work item.  Calls are now torn
     down when their refcount reaches 0 and then handed over to RCU for
     final cleanup.

 (4) Get rid of the rxrpc_call::deadspan timer.  Calls are cleaned up
     immediately they're finished with and don't hang around.
     Post-completion retransmission is handled by the connection processor
     once the call is disconnected.

 (5) Get rid of the dead call expiry setting as there's no longer a timer
     to set.

 (6) rxrpc_destroy_all_calls() can just check that the call list is empty.

Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 5 insertions, 10 deletions

diff --git a/net/rxrpc/ar-internal.h b/net/rxrpc/ar-internal.h
index e3dfc9da05fe..3addda4bfa6b 100644
--- a/net/rxrpc/ar-internal.h
+++ b/net/rxrpc/ar-internal.h
@@ -35,8 +35,6 @@ struct rxrpc_crypt {
 #define rxrpc_queue_delayed_work(WS,D)	\
 	queue_delayed_work(rxrpc_workqueue, (WS), (D))
 
-#define rxrpc_queue_call(CALL)	rxrpc_queue_work(&(CALL)->processor)
-
 struct rxrpc_connection;
 
 /*
@@ -397,7 +395,6 @@ enum rxrpc_call_event {
 	RXRPC_CALL_EV_ACCEPTED,		/* incoming call accepted by userspace app */
 	RXRPC_CALL_EV_SECURED,		/* incoming call's connection is now secure */
 	RXRPC_CALL_EV_POST_ACCEPT,	/* need to post an "accept?" message to the app */
-	RXRPC_CALL_EV_RELEASE,		/* need to release the call's resources */
 };
 
 /*
@@ -417,7 +414,6 @@ enum rxrpc_call_state {
 	RXRPC_CALL_SERVER_SEND_REPLY,	/* - server sending reply */
 	RXRPC_CALL_SERVER_AWAIT_ACK,	/* - server awaiting final ACK */
 	RXRPC_CALL_COMPLETE,		/* - call complete */
-	RXRPC_CALL_DEAD,		/* - call is dead */
 	NR__RXRPC_CALL_STATES
 };
 
@@ -442,12 +438,10 @@ struct rxrpc_call {
 	struct rcu_head		rcu;
 	struct rxrpc_connection	*conn;		/* connection carrying call */
 	struct rxrpc_peer	*peer;		/* Peer record for remote address */
-	struct rxrpc_sock	*socket;	/* socket responsible */
+	struct rxrpc_sock __rcu	*socket;	/* socket responsible */
 	struct timer_list	lifetimer;	/* lifetime remaining on call */
-	struct timer_list	deadspan;	/* reap timer for re-ACK'ing, etc  */
 	struct timer_list	ack_timer;	/* ACK generation timer */
 	struct timer_list	resend_timer;	/* Tx resend timer */
-	struct work_struct	destroyer;	/* call destroyer */
 	struct work_struct	processor;	/* packet processor and ACK generator */
 	rxrpc_notify_rx_t	notify_rx;	/* kernel service Rx notification function */
 	struct list_head	link;		/* link in master call list */
@@ -558,7 +552,6 @@ void rxrpc_process_call(struct work_struct *);
 extern const char *const rxrpc_call_states[];
 extern const char *const rxrpc_call_completions[];
 extern unsigned int rxrpc_max_call_lifetime;
-extern unsigned int rxrpc_dead_call_expiry;
 extern struct kmem_cache *rxrpc_call_jar;
 extern struct list_head rxrpc_calls;
 extern rwlock_t rxrpc_call_lock;
@@ -571,8 +564,10 @@ struct rxrpc_call *rxrpc_new_client_call(struct rxrpc_sock *,
 struct rxrpc_call *rxrpc_incoming_call(struct rxrpc_sock *,
 				       struct rxrpc_connection *,
 				       struct sk_buff *);
-void rxrpc_release_call(struct rxrpc_call *);
+void rxrpc_release_call(struct rxrpc_sock *, struct rxrpc_call *);
 void rxrpc_release_calls_on_socket(struct rxrpc_sock *);
+bool __rxrpc_queue_call(struct rxrpc_call *);
+bool rxrpc_queue_call(struct rxrpc_call *);
 void rxrpc_see_call(struct rxrpc_call *);
 void rxrpc_get_call(struct rxrpc_call *, enum rxrpc_call_trace);
 void rxrpc_put_call(struct rxrpc_call *, enum rxrpc_call_trace);
@@ -835,6 +830,7 @@ extern const char *rxrpc_acks(u8 reason);
 /*
  * output.c
  */
+int rxrpc_send_call_packet(struct rxrpc_call *, u8);
 int rxrpc_send_data_packet(struct rxrpc_connection *, struct sk_buff *);
 
 /*
@@ -880,7 +876,6 @@ extern const struct file_operations rxrpc_connection_seq_fops;
 /*
  * recvmsg.c
  */
-void rxrpc_remove_user_ID(struct rxrpc_sock *, struct rxrpc_call *);
 int rxrpc_recvmsg(struct socket *, struct msghdr *, size_t, int);
 
 /*