Bluetooth: hci_uart: Fix a race for write_work scheduling

In hci_uart_write_work, there is a loop/goto checking the value of
HCI_UART_TX_WAKEUP. If HCI_UART_TX_WAKEUP is set again, it keeps trying
hci_uart_dequeue; otherwise, it clears HCI_UART_SENDING and returns.

In hci_uart_tx_wakeup, if HCI_UART_SENDING is already set, it sets
HCI_UART_TX_WAKEUP, skips schedule_work and assumes the running/pending
hci_uart_write_work worker will do hci_uart_dequeue properly.

However, if the HCI_UART_SENDING check in hci_uart_tx_wakeup is done after
the loop breaks, but before HCI_UART_SENDING is cleared in
hci_uart_write_work, the schedule_work is skipped incorrectly.

Fix this race by changing the order of HCI_UART_SENDING and
HCI_UART_TX_WAKEUP modification.

Fixes: 1da177e ("Linux-2.6.12-rc2")
Fixes: 82f5169 ("Bluetooth: hci_uart: add serdev driver support library")
Signed-off-by: Claire Chang <tientzu@chromium.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

drivers/bluetooth/hci_ldisc.c

@@ -127,10 +127,9 @@ int hci_uart_tx_wakeup(struct hci_uart *hu)
 	if (!test_bit(HCI_UART_PROTO_READY, &hu->flags))
 		goto no_schedule;
 
-	if (test_and_set_bit(HCI_UART_SENDING, &hu->tx_state)) {
-		set_bit(HCI_UART_TX_WAKEUP, &hu->tx_state);
+	set_bit(HCI_UART_TX_WAKEUP, &hu->tx_state);
+	if (test_and_set_bit(HCI_UART_SENDING, &hu->tx_state))
 		goto no_schedule;
-	}
 
 	BT_DBG("");
 
@@ -174,10 +173,10 @@ static void hci_uart_write_work(struct work_struct *work)
 		kfree_skb(skb);
 	}
 
+	clear_bit(HCI_UART_SENDING, &hu->tx_state);
 	if (test_bit(HCI_UART_TX_WAKEUP, &hu->tx_state))
 		goto restart;
 
-	clear_bit(HCI_UART_SENDING, &hu->tx_state);
 	wake_up_bit(&hu->tx_state, HCI_UART_SENDING);
 }
 

drivers/bluetooth/hci_serdev.c

@@ -83,9 +83,9 @@ static void hci_uart_write_work(struct work_struct *work)
 			hci_uart_tx_complete(hu, hci_skb_pkt_type(skb));
 			kfree_skb(skb);
 		}
-	} while (test_bit(HCI_UART_TX_WAKEUP, &hu->tx_state));
 
-	clear_bit(HCI_UART_SENDING, &hu->tx_state);
+		clear_bit(HCI_UART_SENDING, &hu->tx_state);
+	} while (test_bit(HCI_UART_TX_WAKEUP, &hu->tx_state));
 }
 
 /* ------- Interface to HCI layer ------ */