Hi,
Am Samstag, 13. M�rz 2004 15:18 schrieb Juergen Stuber:
> Hi Oliver,
>
> Oliver Neukum <[EMAIL PROTECTED]> writes:
> >
> > [..]
> >> + atomic_t interrupt_in_running;
> >> + atomic_t interrupt_in_done;
> >
> > what use are these atomic declarations?
>
> good question.
> I got this pattern from the use of write_busy in usb-skeleton.c .
> I think it is a safe programming style for concurrently accessed
> variables, but that it isn't strictly necessary if you only read
> and set byte values.
The problem is that it leads to sloppy thinking about locking. People
tend to assume that if they use enough atomic_t races vanish
automagically.
Code like this:
+ atomic_set (&dev->interrupt_in_running, 1);
+ atomic_set (&dev->interrupt_in_done, 0);
+ retval = usb_submit_urb (dev->interrupt_in_urb, GFP_KERNEL);
is potentially racy. It seems to me that you'd rather be clearer with
code like this:
dev->interrupt_in_running = 1;
wmb();
dev->interrupt_in_done = 0;
> > [..]
> >> @@ -628,22 +740,23 @@ static void tower_interrupt_out_callback
> >> {
> >> struct lego_usb_tower *dev = (struct lego_usb_tower *)urb->context;
> >>
> >> - dbg(4," %s : enter, status %d", __func__, urb->status);
> >> - lego_usb_tower_debug_data(5,__func__, urb->actual_length,
> >> urb->transfer_buffer);
> >> + dbg(4, "%s: enter, status %d", __FUNCTION__, urb->status);
> >> + lego_usb_tower_debug_data(5, __FUNCTION__, urb->actual_length,
> >> urb->transfer_buffer);
> >>
> >> if (urb->status != 0) {
> >> - if ((urb->status != -ENOENT) &&
> >> + if ((urb->status != -ENOENT) &&
> >
> > You should also check for ESHUTDOWN.
>
> Ok, and also in the in callback I suppose
> (and that should also be fixed in usb-skeleton, I'll send a patch).
> Btw, are the error codes documented somewhere?
Deep in the introductory pages on http://www.linux-usb.org
Regards
Oliver
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