From 91b5a598b5285da794b72619f31777b62dd336f8 Mon Sep 17 00:00:00 2001 From: Mikhail Gavrilov Date: Wed, 15 Apr 2026 02:52:37 +0500 Subject: Bluetooth: l2cap: defer conn param update to avoid conn->lock/hdev->lock inversion When a BLE peripheral sends an L2CAP Connection Parameter Update Request the processing path is: process_pending_rx() [takes conn->lock] l2cap_le_sig_channel() l2cap_conn_param_update_req() hci_le_conn_update() [takes hdev->lock] Meanwhile other code paths take the locks in the opposite order: l2cap_chan_connect() [takes hdev->lock] ... mutex_lock(&conn->lock) l2cap_conn_ready() [hdev->lock via hci_cb_list_lock] ... mutex_lock(&conn->lock) This is a classic AB/BA deadlock which lockdep reports as a circular locking dependency when connecting a BLE MIDI keyboard (Carry-On FC-49). Fix this by making hci_le_conn_update() defer the HCI command through hci_cmd_sync_queue() so it no longer needs to take hdev->lock in the caller context. The sync callback uses __hci_cmd_sync_status_sk() to wait for the HCI_EV_LE_CONN_UPDATE_COMPLETE event, then updates the stored connection parameters (hci_conn_params) and notifies userspace (mgmt_new_conn_param) only after the controller has confirmed the update. A reference on hci_conn is held via hci_conn_get()/hci_conn_put() for the lifetime of the queued work to prevent use-after-free, and hci_conn_valid() is checked before proceeding in case the connection was removed while the work was pending. The hci_dev_lock is held across hci_conn_valid() and all conn field accesses to prevent a concurrent disconnect from invalidating the connection mid-use. Fixes: f044eb0524a0 ("Bluetooth: Store latency and supervision timeout in connection params") Signed-off-by: Mikhail Gavrilov Reviewed-by: Paul Menzel Signed-off-by: Luiz Augusto von Dentz --- include/net/bluetooth/hci_core.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'include') diff --git a/include/net/bluetooth/hci_core.h b/include/net/bluetooth/hci_core.h index a7bffb908c1e..aa600fbf9a53 100644 --- a/include/net/bluetooth/hci_core.h +++ b/include/net/bluetooth/hci_core.h @@ -2495,7 +2495,7 @@ void mgmt_adv_monitor_device_lost(struct hci_dev *hdev, u16 handle, bdaddr_t *bdaddr, u8 addr_type); int hci_abort_conn(struct hci_conn *conn, u8 reason); -u8 hci_le_conn_update(struct hci_conn *conn, u16 min, u16 max, u16 latency, +void hci_le_conn_update(struct hci_conn *conn, u16 min, u16 max, u16 latency, u16 to_multiplier); void hci_le_start_enc(struct hci_conn *conn, __le16 ediv, __le64 rand, __u8 ltk[16], __u8 key_size); -- cgit v1.2.3