All of lore.kernel.org
 help / color / mirror / Atom feed
From: Marcel Holtmann <marcel@holtmann.org>
To: Dean Jenkins <Dean_Jenkins@mentor.com>
Cc: "Gustavo F. Padovan" <gustavo@padovan.org>,
	Johan Hedberg <johan.hedberg@gmail.com>,
	linux-bluetooth@vger.kernel.org
Subject: Re: [RFC V1 07/16] Bluetooth: hci_ldisc: Add protocol check to hci_uart_tx_wakeup()
Date: Thu, 30 Mar 2017 12:11:34 +0200	[thread overview]
Message-ID: <55813485-14F7-4AB0-8AF4-2D9FE0792019@holtmann.org> (raw)
In-Reply-To: <1490723429-28870-8-git-send-email-Dean_Jenkins@mentor.com>

Hi Dean,

> Before attempting to schedule a work-item onto hu->write_work in
> hci_uart_tx_wakeup(), check that the Data Link protocol layer is
> still bound to the HCI UART driver.
> 
> Failure to perform this protocol check causes a race condition between
> the work queue hu->write_work running hci_uart_write_work() and the
> Data Link protocol layer being unbound (closed) in hci_uart_tty_close().
> 
> Note hci_uart_tty_close() does have a "cancel_work_sync(&hu->write_work)"
> but it is ineffective because it cannot prevent work-items being added
> to hu->write_work after cancel_work_sync() has run.
> 
> Therefore, add a check for HCI_UART_PROTO_READY into hci_uart_tx_wakeup()
> which prevents scheduling of the work queue when HCI_UART_PROTO_READY
> is in the clear state. However, note a small race condition remains
> because the hci_uart_tx_wakeup() thread can run in parallel with the
> hci_uart_tty_close() thread so it is possible that a schedule of
> hu->write_work can occur when HCI_UART_PROTO_READY is cleared. A complete
> solution needs locking of the threads which is implemented in a future
> commit.
> 
> Signed-off-by: Dean Jenkins <Dean_Jenkins@mentor.com>
> ---
> drivers/bluetooth/hci_ldisc.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
> index c4b801b..a1bb4d64b9 100644
> --- a/drivers/bluetooth/hci_ldisc.c
> +++ b/drivers/bluetooth/hci_ldisc.c
> @@ -125,15 +125,19 @@ static inline struct sk_buff *hci_uart_dequeue(struct hci_uart *hu)
> 
> 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);
> -		return 0;
> +		goto no_schedule;
> 	}
> 
> 	BT_DBG("");
> 
> 	schedule_work(&hu->write_work);
> 
> +no_schedule:
> 	return 0;
> }

so instead of calling no_schedule label, just keep calling return 0 directly.

Regards

Marcel


  reply	other threads:[~2017-03-30 10:11 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-03-28 17:50 [RFC V1 00/16] hci_ldisc hci_uart_tty_close() fixes Dean Jenkins
2017-03-28 17:50 ` [RFC V1 01/16] Bluetooth: hci_ldisc: Add missing return in hci_uart_init_work() Dean Jenkins
2017-03-28 17:50 ` [RFC V1 02/16] Bluetooth: hci_ldisc: Ensure hu->hdev set to NULL before freeing hdev Dean Jenkins
2017-03-28 17:50 ` [RFC V1 03/16] Bluetooth: hci_ldisc: Add missing clear HCI_UART_PROTO_READY Dean Jenkins
2017-03-28 17:50 ` [RFC V1 04/16] Bluetooth: hci_ldisc: Add HCI RESET comment to hci_unregister_dev() call Dean Jenkins
2017-03-30 10:11   ` Marcel Holtmann
2017-03-28 17:50 ` [RFC V1 05/16] Bluetooth: hci_ldisc: Add protocol check to hci_uart_send_frame() Dean Jenkins
2017-03-28 17:50 ` [RFC V1 06/16] Bluetooth: hci_ldisc: Add protocol check to hci_uart_dequeue() Dean Jenkins
2017-03-28 17:50 ` [RFC V1 07/16] Bluetooth: hci_ldisc: Add protocol check to hci_uart_tx_wakeup() Dean Jenkins
2017-03-30 10:11   ` Marcel Holtmann [this message]
2017-03-28 17:50 ` [RFC V1 08/16] Bluetooth: hci_ldisc: Separate flag handling in hci_uart_tty_close() Dean Jenkins
2017-03-28 17:50 ` [RFC V1 09/16] Bluetooth: hci_ldisc: Tidy-up HCI_UART_REGISTERED " Dean Jenkins
2017-03-28 17:50 ` [RFC V1 10/16] Bluetooth: hci_ldisc: hci_uart_tty_close() detach tty after last msg Dean Jenkins
2017-03-28 17:50 ` [RFC V1 11/16] Bluetooth: hci_ldisc: hci_uart_tty_close() move hci_uart_close() Dean Jenkins
2017-03-28 17:50 ` [RFC V1 12/16] Bluetooth: hci_ldisc: hci_uart_tty_close() move cancel_work_sync() Dean Jenkins
2017-03-28 17:50 ` [RFC V1 13/16] Bluetooth: hci_ldisc: hci_uart_tty_close() free hu->tx_skb Dean Jenkins
2017-03-28 17:50 ` [RFC V1 14/16] Bluetooth: hci_ldisc: Simplify flushing Dean Jenkins
2017-03-28 17:50 ` [RFC V1 15/16] Bluetooth: hci_ldisc: Use rwlocking to avoid closing proto races Dean Jenkins
2017-03-28 17:50 ` [RFC V1 16/16] Bluetooth: hci_ldisc: Add ioctl_mutex avoiding concurrency Dean Jenkins
2017-03-30 10:11 ` [RFC V1 00/16] hci_ldisc hci_uart_tty_close() fixes Marcel Holtmann
2017-04-03 15:09   ` Dean Jenkins
2017-04-03 15:51     ` Marcel Holtmann
2017-04-04 20:36       ` Dean Jenkins
2017-04-05 15:28         ` Dean Jenkins
2017-04-06  7:23           ` Marcel Holtmann

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=55813485-14F7-4AB0-8AF4-2D9FE0792019@holtmann.org \
    --to=marcel@holtmann.org \
    --cc=Dean_Jenkins@mentor.com \
    --cc=gustavo@padovan.org \
    --cc=johan.hedberg@gmail.com \
    --cc=linux-bluetooth@vger.kernel.org \
    --subject='Re: [RFC V1 07/16] Bluetooth: hci_ldisc: Add protocol check to hci_uart_tx_wakeup()' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.