[PATCH net v2] 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.

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
Signed-off-by: Joonhoe Kim <26rote@gmail.com>
---
Changes in v2:
- Replay the remote's HELLO to the name service from the core once our
  HELLO is out, instead of retrying in announce_servers(). Replaying
  the announcements once hello_sent is set was suggested in the Sashiko
  review of v1. This is also not the delayed work in the name service
  that I mentioned to Mani: that would still miss the broadcasts
  dropped before our HELLO. Nothing sleeps in the name service worker
  and there is no time limit.
- v1: https://lore.kernel.org/all/20261016124600.31-1-26rote@gmail.com/

Tested on a Lenovo Legion Tab Y700 Gen 5 (out-of-tree board support)
with rmtfs started before the modem: the modem's HELLO is still handled
before ours is out ("failed to announce new service"), the replayed
HELLO follows right after, rmtfs gets the modem_fs1/2 opens, and the
modem stays up.

 net/qrtr/af_qrtr.c | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/net/qrtr/af_qrtr.c b/net/qrtr/af_qrtr.c
index e7b364742..508a2dd2d 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 {
@@ -619,7 +626,20 @@ static void qrtr_hello_work(struct work_struct *work)
 	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);
+	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) {
+		pkt->cmd = cpu_to_le32(QRTR_TYPE_HELLO);
+		to.sq_node = READ_ONCE(node->nid);
+		qrtr_local_enqueue(NULL, skb, QRTR_TYPE_HELLO, &to, &from);
+	}
+out:
 	qrtr_port_put(ctrl);
 }
 

base-commit: abeacca61eea4f6803df4a595b656ea45c2d3249
-- 
2.43.0