[Bluez-devel] race condition in hci_usb.c?

[Bluez-devel] race condition in hci_usb.c?

[Jose Vasconcellos]

Hello,

I'm studying the hci_usb driver and I found a possible race condition.
The routine hci_usb_tx_wakeup is called from hci_sub_send_frame
and from hci_usb_tx_complete to get some work done by calling
hci_usb_tx_process. It basically provides serial access to
hci_usb_tx_process by using a couble of bit variables:
HCI_USB_TX_PROCESS and HCI_USB_TX_WAKEPUP.

The problem is that if hci_usb_tx_wakeup is invoked again from a
different context while execution is just terminating hci_usb_tx_process
(right after the while loop), then hci_usb_tx_process will miss the
wakeup. This condition will correct itself when another call is made
to hci_usb_send_frame or another urb finishes transmission.

I experimented by replacing hci_usb_tx_wakeup with a tasklet
that schedules hci_usb_tx_process. This to me seems like a safer
approach.

Regards,

Jose

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Re: [Bluez-devel] race condition in hci_usb.c?

[Marcel Holtmann]

Hi Jose,

> I'm studying the hci_usb driver and I found a possible race condition.
> The routine hci_usb_tx_wakeup is called from hci_sub_send_frame
> and from hci_usb_tx_complete to get some work done by calling
> hci_usb_tx_process. It basically provides serial access to
> hci_usb_tx_process by using a couble of bit variables:
> HCI_USB_TX_PROCESS and HCI_USB_TX_WAKEPUP.
> 
> The problem is that if hci_usb_tx_wakeup is invoked again from a
> different context while execution is just terminating hci_usb_tx_process
> (right after the while loop), then hci_usb_tx_process will miss the
> wakeup. This condition will correct itself when another call is made
> to hci_usb_send_frame or another urb finishes transmission.
> 
> I experimented by replacing hci_usb_tx_wakeup with a tasklet
> that schedules hci_usb_tx_process. This to me seems like a safer
> approach.

feel free to provide a patch. In general the hci_usb driver needs a
complete rewrite anyway.

Regards

Marcel



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