rxrpc: Allow the kernel to mark a call as being non-interruptible

Allow kernel services using AF_RXRPC to indicate that a call should be
non-interruptible. This allows kafs to make things like lock-extension and
writeback data storage calls non-interruptible.

If this is set, signals will be ignored for operations on that call where
possible - such as waiting to get a call channel on an rxrpc connection.

It doesn't prevent UDP sendmsg from being interrupted, but that will be
handled by packet retransmission.

rxrpc_kernel_recv_data() isn't affected by this since that never waits,
preferring instead to return -EAGAIN and leave the waiting to the caller.

Userspace initiated calls can't be set to be uninterruptible at this time.

Signed-off-by: David Howells <[e-mail]>

Documentation/networking/rxrpc.txt

···
 				s64 tx_total_len,
 				gfp_t gfp,
 				rxrpc_notify_rx_t notify_rx,
-				bool upgrade);
+				bool upgrade,
+				bool intr,
+				unsigned int debug_id);
 
      This allocates the infrastructure to make a new RxRPC call and assigns
      call and connection numbers.  The call will be made on the UDP port that
···
      upgrade should be set to true if a client operation should request that
      the server upgrade the service to a better one.  The resultant service ID
      is returned by rxrpc_kernel_recv_data().
+
+     intr should be set to true if the call should be interruptible.  If this
+     is not set, this function may not return until a channel has been
+     allocated; if it is set, the function may return -ERESTARTSYS.
+
+     debug_id is the call debugging ID to be used for tracing.  This can be
+     obtained by atomically incrementing rxrpc_debug_id.
 
      If this function is successful, an opaque reference to the RxRPC call is
      returned.  The caller now holds a reference on this and it must be

fs/afs/rxrpc.c

···
 					  afs_wake_up_async_call :
 					  afs_wake_up_call_waiter),
 					 call->upgrade,
+					 true,
 					 call->debug_id);
 	if (IS_ERR(rxcall)) {
 		ret = PTR_ERR(rxcall);

include/net/af_rxrpc.h

···
 					   gfp_t,
 					   rxrpc_notify_rx_t,
 					   bool,
+					   bool,
 					   unsigned int);
 int rxrpc_kernel_send_data(struct socket *, struct rxrpc_call *,
 			   struct msghdr *, size_t,

net/rxrpc/af_rxrpc.c

···
  * @gfp: The allocation constraints
  * @notify_rx: Where to send notifications instead of socket queue
  * @upgrade: Request service upgrade for call
+ * @intr: The call is interruptible
  * @debug_id: The debug ID for tracing to be assigned to the call
  *
  * Allow a kernel service to begin a call on the nominated socket.  This just
···
 					   gfp_t gfp,
 					   rxrpc_notify_rx_t notify_rx,
 					   bool upgrade,
+					   bool intr,
 					   unsigned int debug_id)
 {
 	struct rxrpc_conn_parameters cp;
···
 	memset(&p, 0, sizeof(p));
 	p.user_call_ID = user_call_ID;
 	p.tx_total_len = tx_total_len;
+	p.intr = intr;
 
 	memset(&cp, 0, sizeof(cp));
 	cp.local		= rx->local;

net/rxrpc/ar-internal.h

···
 	RXRPC_CALL_BEGAN_RX_TIMER,	/* We began the expect_rx_by timer */
 	RXRPC_CALL_RX_HEARD,		/* The peer responded at least once to this call */
 	RXRPC_CALL_RX_UNDERRUN,		/* Got data underrun */
+	RXRPC_CALL_IS_INTR,		/* The call is interruptible */
 };
 
 /*
···
 		u32		normal;		/* Max time since last call packet (msec) */
 	} timeouts;
 	u8			nr_timeouts;	/* Number of timeouts specified */
+	bool			intr;		/* The call is interruptible */
 };
 
 struct rxrpc_send_params {

net/rxrpc/call_object.c

···
 		return call;
 	}
 
+	if (p->intr)
+		__set_bit(RXRPC_CALL_IS_INTR, &call->flags);
 	call->tx_total_len = p->tx_total_len;
 	trace_rxrpc_call(call, rxrpc_call_new_client, atomic_read(&call->usage),
 			 here, (const void *)p->user_call_ID);

net/rxrpc/conn_client.c

···
 
 		add_wait_queue_exclusive(&call->waitq, &myself);
 		for (;;) {
-			set_current_state(TASK_INTERRUPTIBLE);
+			if (test_bit(RXRPC_CALL_IS_INTR, &call->flags))
+				set_current_state(TASK_INTERRUPTIBLE);
+			else
+				set_current_state(TASK_UNINTERRUPTIBLE);
 			if (call->call_id)
 				break;
-			if (signal_pending(current)) {
+			if (test_bit(RXRPC_CALL_IS_INTR, &call->flags) &&
+			    signal_pending(current)) {
 				ret = -ERESTARTSYS;
 				break;
 			}

net/rxrpc/sendmsg.c

···
 		if (call->state >= RXRPC_CALL_COMPLETE)
 			return call->error;
 
-		if (timeout == 0 &&
+		if (test_bit(RXRPC_CALL_IS_INTR, &call->flags) &&
+		    timeout == 0 &&
 		    tx_win == tx_start && signal_pending(current))
 			return -EINTR;
 
···
 		.call.tx_total_len	= -1,
 		.call.user_call_ID	= 0,
 		.call.nr_timeouts	= 0,
+		.call.intr		= true,
 		.abort_code		= 0,
 		.command		= RXRPC_CMD_SEND_DATA,
 		.exclusive		= false,