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Tue, 14 Apr 2026 14:53:04 -0700 (PDT) Received: from localhost ([188.234.148.119]) by smtp.gmail.com with ESMTPSA id 38308e7fff4ca-38e49541dd1sm36227421fa.24.2026.04.14.14.53.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 14 Apr 2026 14:53:04 -0700 (PDT) From: Mikhail Gavrilov To: luiz.dentz@gmail.com, marcel@holtmann.org Cc: pav@iki.fi, pmenzel@molgen.mpg.de, linux-bluetooth@vger.kernel.org, linux-kernel@vger.kernel.org, Mikhail Gavrilov Subject: [PATCH v5] Bluetooth: l2cap: defer conn param update to avoid conn->lock/hdev->lock inversion Date: Wed, 15 Apr 2026 02:52:37 +0500 Message-ID: <20260414215237.17791-1-mikhail.v.gavrilov@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-bluetooth@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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 --- Changes in v5 (Pauli Virtanen, Luiz Augusto von Dentz): - Keep hci_dev_lock held across hci_conn_valid() and all conn field reads (including conn->handle) to close the race window noted by Pauli - Use conn->conn_timeout instead of HCI_CMD_TIMEOUT for the sync wait, matching hci_le_create_conn_sync() pattern Changes in v4 (Luiz Augusto von Dentz, Sashiko/Gemini AI review): - Use hci_conn_get()/hci_conn_put() to hold a reference while work is queued - Use __hci_cmd_sync_status_sk() to wait for HCI_EV_LE_CONN_UPDATE_COMPLETE, then do params update + mgmt notification in the sync callback - Use kzalloc_obj() per checkpatch recommendation Changes in v3 (Luiz Augusto von Dentz): - Move hci_cmd_sync_queue into hci_le_conn_update itself instead of open-coding the deferral in l2cap_core.c - Move conn_params update and mgmt_new_conn_param into hci_le_conn_update_complete_evt, using hci_sent_cmd_data to retrieve the originally requested parameters Changes in v2 (Paul Menzel, Sashiko/Gemini AI review): - Allocate before sending ACCEPTED response to avoid state mismatch on OOM - Verify connection handle and address in sync callback against reuse race - Expand commit message with implementation details include/net/bluetooth/hci_core.h | 2 +- net/bluetooth/hci_conn.c | 105 +++++++++++++++++++++++++------ net/bluetooth/l2cap_core.c | 12 +--- 3 files changed, 89 insertions(+), 30 deletions(-) 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); diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c index 11d3ad8d2551..fea0764b8ba3 100644 --- a/net/bluetooth/hci_conn.c +++ b/net/bluetooth/hci_conn.c @@ -480,40 +480,107 @@ bool hci_setup_sync(struct hci_conn *conn, __u16 handle) return hci_setup_sync_conn(conn, handle); } -u8 hci_le_conn_update(struct hci_conn *conn, u16 min, u16 max, u16 latency, - u16 to_multiplier) +struct le_conn_update_data { + struct hci_conn *conn; + u16 min; + u16 max; + u16 latency; + u16 to_multiplier; +}; + +static int le_conn_update_sync(struct hci_dev *hdev, void *data) { - struct hci_dev *hdev = conn->hdev; + struct le_conn_update_data *d = data; + struct hci_conn *conn = d->conn; struct hci_conn_params *params; struct hci_cp_le_conn_update cp; + u16 timeout; + u8 store_hint; + int err; + /* Verify connection is still alive and read conn fields under + * the same lock to prevent a concurrent disconnect from freeing + * or reusing the connection while we build the HCI command. + */ hci_dev_lock(hdev); - params = hci_conn_params_lookup(hdev, &conn->dst, conn->dst_type); - if (params) { - params->conn_min_interval = min; - params->conn_max_interval = max; - params->conn_latency = latency; - params->supervision_timeout = to_multiplier; + if (!hci_conn_valid(hdev, conn)) { + hci_dev_unlock(hdev); + return -ECANCELED; } - hci_dev_unlock(hdev); - memset(&cp, 0, sizeof(cp)); cp.handle = cpu_to_le16(conn->handle); - cp.conn_interval_min = cpu_to_le16(min); - cp.conn_interval_max = cpu_to_le16(max); - cp.conn_latency = cpu_to_le16(latency); - cp.supervision_timeout = cpu_to_le16(to_multiplier); + cp.conn_interval_min = cpu_to_le16(d->min); + cp.conn_interval_max = cpu_to_le16(d->max); + cp.conn_latency = cpu_to_le16(d->latency); + cp.supervision_timeout = cpu_to_le16(d->to_multiplier); cp.min_ce_len = cpu_to_le16(0x0000); cp.max_ce_len = cpu_to_le16(0x0000); + timeout = conn->conn_timeout; + + hci_dev_unlock(hdev); + + err = __hci_cmd_sync_status_sk(hdev, HCI_OP_LE_CONN_UPDATE, + sizeof(cp), &cp, + HCI_EV_LE_CONN_UPDATE_COMPLETE, + timeout, NULL); + if (err) + return err; + + /* Update stored connection parameters after the controller has + * confirmed the update via the LE Connection Update Complete event. + */ + hci_dev_lock(hdev); + + params = hci_conn_params_lookup(hdev, &conn->dst, conn->dst_type); + if (params) { + params->conn_min_interval = d->min; + params->conn_max_interval = d->max; + params->conn_latency = d->latency; + params->supervision_timeout = d->to_multiplier; + store_hint = 0x01; + } else { + store_hint = 0x00; + } - hci_send_cmd(hdev, HCI_OP_LE_CONN_UPDATE, sizeof(cp), &cp); + hci_dev_unlock(hdev); - if (params) - return 0x01; + mgmt_new_conn_param(hdev, &conn->dst, conn->dst_type, store_hint, + d->min, d->max, d->latency, d->to_multiplier); - return 0x00; + return 0; +} + +static void le_conn_update_complete(struct hci_dev *hdev, void *data, int err) +{ + struct le_conn_update_data *d = data; + + hci_conn_put(d->conn); + kfree(d); +} + +void hci_le_conn_update(struct hci_conn *conn, u16 min, u16 max, u16 latency, + u16 to_multiplier) +{ + struct le_conn_update_data *d; + + d = kzalloc_obj(*d); + if (!d) + return; + + hci_conn_get(conn); + d->conn = conn; + d->min = min; + d->max = max; + d->latency = latency; + d->to_multiplier = to_multiplier; + + if (hci_cmd_sync_queue(conn->hdev, le_conn_update_sync, d, + le_conn_update_complete) < 0) { + hci_conn_put(conn); + kfree(d); + } } void hci_le_start_enc(struct hci_conn *conn, __le16 ediv, __le64 rand, diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c index 95c65fece39b..aac2db1d6fbb 100644 --- a/net/bluetooth/l2cap_core.c +++ b/net/bluetooth/l2cap_core.c @@ -4706,16 +4706,8 @@ static inline int l2cap_conn_param_update_req(struct l2cap_conn *conn, l2cap_send_cmd(conn, cmd->ident, L2CAP_CONN_PARAM_UPDATE_RSP, sizeof(rsp), &rsp); - if (!err) { - u8 store_hint; - - store_hint = hci_le_conn_update(hcon, min, max, latency, - to_multiplier); - mgmt_new_conn_param(hcon->hdev, &hcon->dst, hcon->dst_type, - store_hint, min, max, latency, - to_multiplier); - - } + if (!err) + hci_le_conn_update(hcon, min, max, latency, to_multiplier); return 0; } -- 2.53.0