[PATCH] Bluetooth: hci_sync: annotate data-races around hdev->req_status

[Cen Zhang]

__hci_cmd_sync_sk() sets hdev->req_status under hdev->req_lock:

    hdev->req_status = HCI_REQ_PEND;

However, several other functions read or write hdev->req_status without
holding any lock:

  - hci_send_cmd_sync() reads req_status in hci_cmd_work (workqueue)
  - hci_cmd_sync_complete() reads/writes from HCI event completion
  - hci_cmd_sync_cancel() / hci_cmd_sync_cancel_sync() read/write
  - hci_abort_conn() reads in connection abort path

Since __hci_cmd_sync_sk() runs on hdev->req_workqueue while
hci_send_cmd_sync() runs on hdev->workqueue, these are different
workqueues that can execute concurrently on different CPUs. The plain
C accesses constitute a data race.

Add READ_ONCE()/WRITE_ONCE() annotations on all concurrent accesses
to hdev->req_status to prevent potential compiler optimizations that
could affect correctness (e.g., load fusing in the wait_event
condition or store reordering).

Signed-off-by: Cen Zhang <zzzccc427@xxxxxxxxx>
---
 net/bluetooth/hci_conn.c |  2 +-
 net/bluetooth/hci_core.c |  2 +-
 net/bluetooth/hci_sync.c | 20 ++++++++++----------
 3 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
index 4719dac07190..81c4df0ade0f 100644
--- a/net/bluetooth/hci_conn.c
+++ b/net/bluetooth/hci_conn.c
@@ -3095,7 +3095,7 @@ int hci_abort_conn(struct hci_conn *conn, u8 reason)
 	 * hci_connect_le serializes the connection attempts so only one
 	 * connection can be in BT_CONNECT at time.
 	 */
-	if (conn->state == BT_CONNECT && hdev->req_status == HCI_REQ_PEND) {
+	if (conn->state == BT_CONNECT && READ_ONCE(hdev->req_status) == HCI_REQ_PEND) {
 		switch (hci_skb_event(hdev->sent_cmd)) {
 		case HCI_EV_CONN_COMPLETE:
 		case HCI_EV_LE_CONN_COMPLETE:
diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
index 31308c1de4ec..01f8ceeb1c0c 100644
--- a/net/bluetooth/hci_core.c
+++ b/net/bluetooth/hci_core.c
@@ -4126,7 +4126,7 @@ static int hci_send_cmd_sync(struct hci_dev *hdev, struct sk_buff *skb)
 		kfree_skb(skb);
 	}
 
-	if (hdev->req_status == HCI_REQ_PEND &&
+	if (READ_ONCE(hdev->req_status) == HCI_REQ_PEND &&
 	    !hci_dev_test_and_set_flag(hdev, HCI_CMD_PENDING)) {
 		kfree_skb(hdev->req_skb);
 		hdev->req_skb = skb_clone(hdev->sent_cmd, GFP_KERNEL);
diff --git a/net/bluetooth/hci_sync.c b/net/bluetooth/hci_sync.c
index 121dbc8208ec..335ec52a8e99 100644
--- a/net/bluetooth/hci_sync.c
+++ b/net/bluetooth/hci_sync.c
@@ -25,11 +25,11 @@ static void hci_cmd_sync_complete(struct hci_dev *hdev, u8 result, u16 opcode,
 {
 	bt_dev_dbg(hdev, "result 0x%2.2x", result);
 
-	if (hdev->req_status != HCI_REQ_PEND)
+	if (READ_ONCE(hdev->req_status) != HCI_REQ_PEND)
 		return;
 
 	hdev->req_result = result;
-	hdev->req_status = HCI_REQ_DONE;
+	WRITE_ONCE(hdev->req_status, HCI_REQ_DONE);
 
 	/* Free the request command so it is not used as response */
 	kfree_skb(hdev->req_skb);
@@ -167,20 +167,20 @@ struct sk_buff *__hci_cmd_sync_sk(struct hci_dev *hdev, u16 opcode, u32 plen,
 
 	hci_cmd_sync_add(&req, opcode, plen, param, event, sk);
 
-	hdev->req_status = HCI_REQ_PEND;
+	WRITE_ONCE(hdev->req_status, HCI_REQ_PEND);
 
 	err = hci_req_sync_run(&req);
 	if (err < 0)
 		return ERR_PTR(err);
 
 	err = wait_event_interruptible_timeout(hdev->req_wait_q,
-					       hdev->req_status != HCI_REQ_PEND,
+					       READ_ONCE(hdev->req_status) != HCI_REQ_PEND,
 					       timeout);
 
 	if (err == -ERESTARTSYS)
 		return ERR_PTR(-EINTR);
 
-	switch (hdev->req_status) {
+	switch (READ_ONCE(hdev->req_status)) {
 	case HCI_REQ_DONE:
 		err = -bt_to_errno(hdev->req_result);
 		break;
@@ -194,7 +194,7 @@ struct sk_buff *__hci_cmd_sync_sk(struct hci_dev *hdev, u16 opcode, u32 plen,
 		break;
 	}
 
-	hdev->req_status = 0;
+	WRITE_ONCE(hdev->req_status, 0);
 	hdev->req_result = 0;
 	skb = hdev->req_rsp;
 	hdev->req_rsp = NULL;
@@ -665,9 +665,9 @@ void hci_cmd_sync_cancel(struct hci_dev *hdev, int err)
 {
 	bt_dev_dbg(hdev, "err 0x%2.2x", err);
 
-	if (hdev->req_status == HCI_REQ_PEND) {
+	if (READ_ONCE(hdev->req_status) == HCI_REQ_PEND) {
 		hdev->req_result = err;
-		hdev->req_status = HCI_REQ_CANCELED;
+		WRITE_ONCE(hdev->req_status, HCI_REQ_CANCELED);
 
 		queue_work(hdev->workqueue, &hdev->cmd_sync_cancel_work);
 	}
@@ -683,12 +683,12 @@ void hci_cmd_sync_cancel_sync(struct hci_dev *hdev, int err)
 {
 	bt_dev_dbg(hdev, "err 0x%2.2x", err);
 
-	if (hdev->req_status == HCI_REQ_PEND) {
+	if (READ_ONCE(hdev->req_status) == HCI_REQ_PEND) {
 		/* req_result is __u32 so error must be positive to be properly
 		 * propagated.
 		 */
 		hdev->req_result = err < 0 ? -err : err;
-		hdev->req_status = HCI_REQ_CANCELED;
+		WRITE_ONCE(hdev->req_status, HCI_REQ_CANCELED);
 
 		wake_up_interruptible(&hdev->req_wait_q);
 	}
-- 
2.34.1