net: qrtr: Send HELLO message on endpoint register

HELLO is currently handled entirely by the name server (NS): it is
sent once as a broadcast when the NS initializes, and again as a
reply whenever the NS receives an inbound HELLO from a remote.

Some remote QRTR endpoints (e.g. an external WLAN chipset attached
over MHI) operate in a slave role: they only ever send a HELLO in
response to one they receive, and never initiate. Since the host cannot
tell in advance which remotes behave this way, if the host also only
replies, both sides wait on the other to speak first and no HELLO is
ever exchanged, stalling further communication.

To fix this:
- Transfer HELLO handshake ownership to the core layer. A HELLO is
  now sent once, per endpoint, at registration time.
- Schedule a delayed work item on endpoint registration to send a
  HELLO once the name server is bound. The work reschedules itself
  with a 100ms backoff if the name server socket is not yet bound or
  if allocating the control packet fails, so a transient startup
  condition does not abandon the handshake permanently.
- Enforce HELLO-first ordering by dropping non-HELLO packets and
  returning -EAGAIN until the HELLO is confirmed sent, using bool
  hello_sent guarded by ep_lock to make the gate check atomic with
  xmit().
- Skip nodes with nid == QRTR_EP_NID_AUTO in bcast_enqueue(), to avoid
  broadcasting control packets with QRTR_EP_NID_AUTO as the destination
  node ID.
- Remove say_hello() from the name server's ctrl_cmd_hello() handler
  and from qrtr_ns_init(); the core layer is now the sole sender of
  the outbound HELLO. This removes the NS's reply-on-receive
  behaviour without a replacement.

Signed-off-by: Chris Lew <christopher.lew@oss.qualcomm.com>
Co-developed-by: Deepak Kumar Singh <deepak.singh@oss.qualcomm.com>
Signed-off-by: Deepak Kumar Singh <deepak.singh@oss.qualcomm.com>
Co-developed-by: Pranav Mahesh Phansalkar <pranav.phansalkar@oss.qualcomm.com>
Signed-off-by: Pranav Mahesh Phansalkar <pranav.phansalkar@oss.qualcomm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/qrtr/af_qrtr.c

@@ -9,6 +9,7 @@
 #include <linux/termios.h>	/* For TIOCINQ/OUTQ */
 #include <linux/spinlock.h>
 #include <linux/wait.h>
+#include <linux/workqueue.h>
 
 #include <net/sock.h>
 
@@ -120,8 +121,10 @@ static DEFINE_XARRAY_ALLOC(qrtr_ports);
  * @nid: node id
  * @qrtr_tx_flow: xarray of qrtr_tx_flow, keyed by node << 32 | port
  * @qrtr_tx_lock: lock for qrtr_tx_flow inserts
+ * @hello_sent: hello packet send successful
  * @rx_queue: receive queue
  * @item: list item for broadcast list
+ * @say_hello: delayed work for sending hello packet
  */
 struct qrtr_node {
 	struct mutex ep_lock;
@@ -132,8 +135,11 @@ struct qrtr_node {
 	struct xarray qrtr_tx_flow;
 	struct mutex qrtr_tx_lock; /* for qrtr_tx_flow */
 
+	bool hello_sent;
+
 	struct sk_buff_head rx_queue;
 	struct list_head item;
+	struct delayed_work say_hello;
 };
 
 /**
@@ -187,6 +193,8 @@ static void __qrtr_node_release(struct kref *kref)
 	list_del(&node->item);
 	mutex_unlock(&qrtr_node_lock);
 
+	cancel_delayed_work_sync(&node->say_hello);
+
 	skb_queue_purge(&node->rx_queue);
 
 	/* Free tx flow counters */
@@ -341,6 +349,14 @@ static int qrtr_node_enqueue(struct qrtr_node *node, struct sk_buff *skb,
 	size_t len = skb->len;
 	int rc, confirm_rx;
 
+	mutex_lock(&node->ep_lock);
+	if (!node->hello_sent && type != QRTR_TYPE_HELLO) {
+		mutex_unlock(&node->ep_lock);
+		kfree_skb(skb);
+		return -EAGAIN;
+	}
+	mutex_unlock(&node->ep_lock);
+
 	confirm_rx = qrtr_tx_wait(node, to->sq_node, to->sq_port, type);
 	if (confirm_rx < 0) {
 		kfree_skb(skb);
@@ -353,7 +369,7 @@ static int qrtr_node_enqueue(struct qrtr_node *node, struct sk_buff *skb,
 	hdr->src_node_id = cpu_to_le32(from->sq_node);
 	hdr->src_port_id = cpu_to_le32(from->sq_port);
 	if (to->sq_port == QRTR_PORT_CTRL) {
-		hdr->dst_node_id = cpu_to_le32(node->nid);
+		hdr->dst_node_id = cpu_to_le32(READ_ONCE(node->nid));
 		hdr->dst_port_id = cpu_to_le32(QRTR_PORT_CTRL);
 	} else {
 		hdr->dst_node_id = cpu_to_le32(to->sq_node);
@@ -372,6 +388,8 @@ static int qrtr_node_enqueue(struct qrtr_node *node, struct sk_buff *skb,
 			rc = node->ep->xmit(node->ep, skb);
 		else
 			kfree_skb(skb);
+		if (!rc && type == QRTR_TYPE_HELLO)
+			node->hello_sent = true;
 		mutex_unlock(&node->ep_lock);
 	}
 	/* Need to ensure that a subsequent message carries the otherwise lost
@@ -379,6 +397,9 @@ static int qrtr_node_enqueue(struct qrtr_node *node, struct sk_buff *skb,
 	if (rc && confirm_rx)
 		qrtr_tx_flow_failed(node, to->sq_node, to->sq_port);
 
+	if (rc == -EAGAIN && type == QRTR_TYPE_HELLO)
+		schedule_delayed_work(&node->say_hello, msecs_to_jiffies(100));
+
 	return rc;
 }
 
@@ -416,7 +437,7 @@ static void qrtr_node_assign(struct qrtr_node *node, unsigned int nid)
 	spin_lock_irqsave(&qrtr_nodes_lock, flags);
 	radix_tree_insert(&qrtr_nodes, nid, node);
 	if (node->nid == QRTR_EP_NID_AUTO)
-		node->nid = nid;
+		WRITE_ONCE(node->nid, nid);
 	spin_unlock_irqrestore(&qrtr_nodes_lock, flags);
 }
 
@@ -570,6 +591,38 @@ static struct sk_buff *qrtr_alloc_ctrl_packet(struct qrtr_ctrl_pkt **pkt,
 	return skb;
 }
 
+static void qrtr_hello_work(struct work_struct *work)
+{
+	struct sockaddr_qrtr from = {AF_QIPCRTR, 0, QRTR_PORT_CTRL};
+	struct sockaddr_qrtr to = {AF_QIPCRTR, 0, QRTR_PORT_CTRL};
+	struct qrtr_ctrl_pkt *pkt;
+	struct qrtr_node *node;
+	struct qrtr_sock *ctrl;
+	struct sk_buff *skb;
+
+	node = container_of(to_delayed_work(work), struct qrtr_node, say_hello);
+
+	/* NS must be bound before we can send; retry with backoff if not ready */
+	ctrl = qrtr_port_lookup(QRTR_PORT_CTRL);
+	if (!ctrl) {
+		schedule_delayed_work(&node->say_hello, msecs_to_jiffies(100));
+		return;
+	}
+
+	skb = qrtr_alloc_ctrl_packet(&pkt, GFP_KERNEL);
+	if (!skb) {
+		qrtr_port_put(ctrl);
+		schedule_delayed_work(&node->say_hello, msecs_to_jiffies(100));
+		return;
+	}
+
+	pkt->cmd = cpu_to_le32(QRTR_TYPE_HELLO);
+	from.sq_node = qrtr_local_nid;
+	to.sq_node = node->nid;
+	qrtr_node_enqueue(node, skb, QRTR_TYPE_HELLO, &from, &to);
+	qrtr_port_put(ctrl);
+}
+
 /**
  * qrtr_endpoint_register() - register a new endpoint
  * @ep: endpoint to register
@@ -595,6 +648,9 @@ int qrtr_endpoint_register(struct qrtr_endpoint *ep, unsigned int nid)
 	node->nid = QRTR_EP_NID_AUTO;
 	node->ep = ep;
 
+	node->hello_sent = false;
+	INIT_DELAYED_WORK(&node->say_hello, qrtr_hello_work);
+
 	xa_init(&node->qrtr_tx_flow);
 	mutex_init(&node->qrtr_tx_lock);
 
@@ -605,6 +661,9 @@ int qrtr_endpoint_register(struct qrtr_endpoint *ep, unsigned int nid)
 	mutex_unlock(&qrtr_node_lock);
 	ep->node = node;
 
+	/* Initiate HELLO handshake from the core layer */
+	schedule_delayed_work(&node->say_hello, 0);
+
 	return 0;
 }
 EXPORT_SYMBOL_GPL(qrtr_endpoint_register);
@@ -879,6 +938,9 @@ static int qrtr_bcast_enqueue(struct qrtr_node *node, struct sk_buff *skb,
 
 	mutex_lock(&qrtr_node_lock);
 	list_for_each_entry(node, &qrtr_all_nodes, item) {
+		/* Skip nodes with no assigned node ID yet. */
+		if (READ_ONCE(node->nid) == QRTR_EP_NID_AUTO)
+			continue;
 		skbn = pskb_copy(skb, GFP_KERNEL);
 		if (!skbn)
 			break;

net/qrtr/ns.c

@@ -212,6 +212,7 @@ static void lookup_notify(struct sockaddr_qrtr *to, struct qrtr_server *srv,
 		pr_err("failed to send lookup notification\n");
 }
 
+/* Announce the list of servers registered on the local node */
 static int announce_servers(struct sockaddr_qrtr *sq)
 {
 	struct qrtr_server *srv;
@@ -326,38 +327,8 @@ static int server_del(struct qrtr_node *node, unsigned int port, bool bcast)
 	return 0;
 }
 
-static int say_hello(struct sockaddr_qrtr *dest)
-{
-	struct qrtr_ctrl_pkt pkt;
-	struct msghdr msg = { };
-	struct kvec iv;
-	int ret;
-
-	iv.iov_base = &pkt;
-	iv.iov_len = sizeof(pkt);
-
-	memset(&pkt, 0, sizeof(pkt));
-	pkt.cmd = cpu_to_le32(QRTR_TYPE_HELLO);
-
-	msg.msg_name = (struct sockaddr *)dest;
-	msg.msg_namelen = sizeof(*dest);
-
-	ret = kernel_sendmsg(qrtr_ns.sock, &msg, &iv, 1, sizeof(pkt));
-	if (ret < 0)
-		pr_err("failed to send hello msg\n");
-
-	return ret;
-}
-
-/* Announce the list of servers registered on the local node */
 static int ctrl_cmd_hello(struct sockaddr_qrtr *sq)
 {
-	int ret;
-
-	ret = say_hello(sq);
-	if (ret < 0)
-		return ret;
-
 	return announce_servers(sq);
 }
 
@@ -774,10 +745,6 @@ int qrtr_ns_init(void)
 	qrtr_ns.bcast_sq.sq_node = QRTR_NODE_BCAST;
 	qrtr_ns.bcast_sq.sq_port = QRTR_PORT_CTRL;
 
-	ret = say_hello(&qrtr_ns.bcast_sq);
-	if (ret < 0)
-		goto err_wq;
-
 	/* As the qrtr ns socket owner and creator is the same module, we have
 	 * to decrease the qrtr module reference count to guarantee that it
 	 * remains zero after the ns socket is created, otherwise, executing