Re: [PATCHv3] Input: xpad - Fix double URB submission races

From: Dmitry Torokhov
Date: Thu Dec 10 2015 - 01:45:52 EST


Hi Laura,

On Mon, Nov 16, 2015 at 02:47:13PM -0800, Laura Abbott wrote:
> +static int __xpad_submit_urb(struct usb_xpad *xpad,
> + unsigned char odata[XPAD_PKT_LEN], int transfer_length,
> + int type, bool safe_submit)
> +{
> + int ret;
> +
> + if (safe_submit || xpad->submit_state == OUT_IRQ_AVAILABLE) {
> + memcpy(xpad->odata, odata, transfer_length);
> + xpad->irq_out->transfer_buffer_length = transfer_length;
> + ret = usb_submit_urb(xpad->irq_out, GFP_ATOMIC);
> + xpad->submit_state = OUT_IRQ_QUEUE_EMPTY;
> + xpad->out_submitter = type;
> + } else {
> + /*
> + * The goal here is to prevent starvation of any other type.
> + * If this type matches what is being submitted and there is
> + * another type in the queue, don't ovewrite it
> + */
> + if (xpad->submit_state != OUT_IRQ_QUEUE_EMPTY &&
> + xpad->out_submitter == type &&
> + xpad->queue_submitter != type) {
> + ret = -EBUSY;
> + goto out;

No, we do not want to return "busy" here. We should save the most
up-to-date request of given type and re-submit it when URB is no longer
busy.

I CCed you on another patch addressing the same issue, please take a
look when you have a chance.

Thanks.

--
Dmitry
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