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

Jose Vasconcellos
2006-09-22T18:08:42Z

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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