[PATCH net v3] net: qrtr: announce local services again once our HELLO is sent

[Joonhoe Kim <26rote@gmail.com>]

Since commit 544d85de4dc2 ("net: qrtr: Send HELLO message on endpoint
register"), qrtr_node_enqueue() drops every packet but HELLO with
-EAGAIN until our HELLO has gone out to the node. When the remote's
HELLO arrives first, the NEW_SERVER replies from the name service are
dropped, and so are the broadcasts for services registered before our
HELLO goes out. Nothing announces these services again, so the remote
never learns about them.

On Kaanapali the modem sends its HELLO before it accepts ours. With
rmtfs started first, the modem never learns about rmtfs and its
watchdog resets the SoC about 40 s later.

Remember that the remote has sent a HELLO. Once our HELLO has been
sent to such a node, pass a HELLO from it to the local name service
again, so that it announces the services it has at that point. Retry
the replay if it cannot be queued, and queue it under ep_lock only
while the endpoint is registered, so that it cannot follow the BYE
from qrtr_endpoint_unregister().

The flag is not cleared when qrtr_endpoint_hello() restarts the
handshake on resume, so a HELLO that the remote sent before then is
not lost. The cost is that the remote gets the same NEW_SERVER
announcements twice when its HELLO arrives before ours goes out but
the name service handles it after, and on every resume.

Fixes: 544d85de4dc2 ("net: qrtr: Send HELLO message on endpoint register")
Cc: stable@vger.kernel.org
Tested-by: Filippo Falezza <effeffe99@gmail.com> # Motorola Moto G 5G Plus nairo (SM7250)
Signed-off-by: Joonhoe Kim <26rote@gmail.com>
---
Changes in v3:
- Retry the replayed HELLO if it cannot be allocated or queued, without
  sending our HELLO again [Mani, Sashiko]
- Queue the replayed HELLO under ep_lock only while node->ep is set, so
  that it is ordered before the BYE from qrtr_endpoint_unregister()
  [Sashiko]
- Keep Filippo's Tested-by from v2: when nothing fails, v3 only adds the
  ep_lock around queueing the replay
- v2: https://lore.kernel.org/all/20261022163116.1042-1-26rote@gmail.com/

Tested on a Lenovo Y700 Gen 5 (TB323FU, Kaanapali; out-of-tree board
support) with rmtfs started before the modem: the replayed HELLO
follows the modem's, rmtfs gets the modem_fs1/2 opens and the modem
stays up, also with an error injected into the first replay, which is
then retried.

 net/qrtr/af_qrtr.c | 53 +++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 45 insertions(+), 8 deletions(-)

diff --git a/net/qrtr/af_qrtr.c b/net/qrtr/af_qrtr.c
index e7b364742..45cb8e8c3 100644
--- a/net/qrtr/af_qrtr.c
+++ b/net/qrtr/af_qrtr.c
@@ -122,6 +122,7 @@ static DEFINE_XARRAY_ALLOC(qrtr_ports);
  * @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
+ * @hello_rcvd: remote has sent a hello packet
  * @rx_queue: receive queue
  * @item: list item for broadcast list
  * @say_hello: delayed work for sending hello packet
@@ -136,6 +137,7 @@ struct qrtr_node {
 	struct mutex qrtr_tx_lock; /* for qrtr_tx_flow */
 
 	bool hello_sent;
+	bool hello_rcvd;
 
 	struct sk_buff_head rx_queue;
 	struct list_head item;
@@ -541,6 +543,11 @@ int qrtr_endpoint_post(struct qrtr_endpoint *ep, const void *data, size_t len)
 		qrtr_node_assign(node, le32_to_cpu(pkt->server.node));
 	}
 
+	if (cb->type == QRTR_TYPE_HELLO) {
+		/* Pairs with smp_load_acquire() in qrtr_hello_work() */
+		smp_store_release(&node->hello_rcvd, true);
+	}
+
 	if (cb->type == QRTR_TYPE_RESUME_TX) {
 		qrtr_tx_resume(node, skb);
 	} else {
@@ -599,6 +606,8 @@ static void qrtr_hello_work(struct work_struct *work)
 	struct qrtr_node *node;
 	struct qrtr_sock *ctrl;
 	struct sk_buff *skb;
+	bool hello_sent;
+	int rc = 0;
 
 	node = container_of(to_delayed_work(work), struct qrtr_node, say_hello);
 
@@ -609,17 +618,45 @@ static void qrtr_hello_work(struct work_struct *work)
 		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;
+	mutex_lock(&node->ep_lock);
+	hello_sent = node->hello_sent;
+	mutex_unlock(&node->ep_lock);
+
+	from.sq_node = qrtr_local_nid;
+	if (!hello_sent) {
+		skb = qrtr_alloc_ctrl_packet(&pkt, GFP_KERNEL);
+		if (!skb)
+			goto retry;
+
+		pkt->cmd = cpu_to_le32(QRTR_TYPE_HELLO);
+		to.sq_node = node->nid;
+		if (qrtr_node_enqueue(node, skb, QRTR_TYPE_HELLO, &from, &to))
+			goto out;
 	}
 
+	/* Pairs with smp_store_release() in qrtr_endpoint_post() */
+	if (!smp_load_acquire(&node->hello_rcvd))
+		goto out;
+
+	skb = qrtr_alloc_ctrl_packet(&pkt, GFP_KERNEL);
+	if (!skb)
+		goto retry;
+
 	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);
+	to.sq_node = READ_ONCE(node->nid);
+
+	mutex_lock(&node->ep_lock);
+	if (node->ep)
+		rc = qrtr_local_enqueue(NULL, skb, QRTR_TYPE_HELLO, &to, &from);
+	else
+		kfree_skb(skb);
+	mutex_unlock(&node->ep_lock);
+	if (!rc)
+		goto out;
+
+retry:
+	schedule_delayed_work(&node->say_hello, msecs_to_jiffies(100));
+out:
 	qrtr_port_put(ctrl);
 }
 

base-commit: abeacca61eea4f6803df4a595b656ea45c2d3249
-- 
2.43.0