Re: [PATCH 09/11] bluetooth: hci_ldisc: fix deadlock condition

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[ +to Marcel Holtmann ]

On 03/20/2014 03:30 PM, Felipe Balbi wrote:
LDISCs shouldn't call tty->ops->write() from within
->write_wakeup().

->write_wakeup() is called with port lock taken and
IRQs disabled, tty->ops->write() will try to acquire
the same port lock and we will deadlock.

Reviewed-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
Reported-by: Huang Shijie <b32955@xxxxxxxxxxxxx>
Signed-off-by: Felipe Balbi <balbi@xxxxxx>

I just noticed this patch wasn't addressed to Marcel;
seems like this should go through the bluetooth tree (but not
through bluetooth-next because it fixes an oops).

Marcel,

You may want to build on top of this patch split handling;
I noticed some of the protocol drivers are calling
hci_uart_tx_wakeup() from work functions already (so don't
need to schedule another work...)

Regards,
Peter Hurley

---
  drivers/bluetooth/hci_ldisc.c | 24 +++++++++++++++++++-----
  drivers/bluetooth/hci_uart.h  |  1 +
  2 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
index 6e06f6f..77af52f 100644
--- a/drivers/bluetooth/hci_ldisc.c
+++ b/drivers/bluetooth/hci_ldisc.c
@@ -118,10 +118,6 @@ static inline struct sk_buff *hci_uart_dequeue(struct hci_uart *hu)

  int hci_uart_tx_wakeup(struct hci_uart *hu)
  {
-	struct tty_struct *tty = hu->tty;
-	struct hci_dev *hdev = hu->hdev;
-	struct sk_buff *skb;
-
  	if (test_and_set_bit(HCI_UART_SENDING, &hu->tx_state)) {
  		set_bit(HCI_UART_TX_WAKEUP, &hu->tx_state);
  		return 0;
@@ -129,6 +125,22 @@ int hci_uart_tx_wakeup(struct hci_uart *hu)

  	BT_DBG("");

+	schedule_work(&hu->write_work);
+
+	return 0;
+}
+
+static void hci_uart_write_work(struct work_struct *work)
+{
+	struct hci_uart *hu = container_of(work, struct hci_uart, write_work);
+	struct tty_struct *tty = hu->tty;
+	struct hci_dev *hdev = hu->hdev;
+	struct sk_buff *skb;
+
+	/* REVISIT: should we cope with bad skbs or ->write() returning
+	 * and error value ?
+	 */
+
  restart:
  	clear_bit(HCI_UART_TX_WAKEUP, &hu->tx_state);

@@ -153,7 +165,6 @@ restart:
  		goto restart;

  	clear_bit(HCI_UART_SENDING, &hu->tx_state);
-	return 0;
  }

  static void hci_uart_init_work(struct work_struct *work)
@@ -281,6 +292,7 @@ static int hci_uart_tty_open(struct tty_struct *tty)
  	tty->receive_room = 65536;

  	INIT_WORK(&hu->init_ready, hci_uart_init_work);
+	INIT_WORK(&hu->write_work, hci_uart_write_work);

  	spin_lock_init(&hu->rx_lock);

@@ -318,6 +330,8 @@ static void hci_uart_tty_close(struct tty_struct *tty)
  	if (hdev)
  		hci_uart_close(hdev);

+	cancel_work_sync(&hu->write_work);
+
  	if (test_and_clear_bit(HCI_UART_PROTO_SET, &hu->flags)) {
  		if (hdev) {
  			if (test_bit(HCI_UART_REGISTERED, &hu->flags))
diff --git a/drivers/bluetooth/hci_uart.h b/drivers/bluetooth/hci_uart.h
index fffa61f..12df101 100644
--- a/drivers/bluetooth/hci_uart.h
+++ b/drivers/bluetooth/hci_uart.h
@@ -68,6 +68,7 @@ struct hci_uart {
  	unsigned long		hdev_flags;

  	struct work_struct	init_ready;
+	struct work_struct	write_work;

  	struct hci_uart_proto	*proto;
  	void			*priv;


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