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    SubjectRe: [PATCH v2 3/5] ALSA: xen-front: Implement Xen event channel handling
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    On 04/24/2018 05:20 PM, Takashi Iwai wrote:
    > On Mon, 16 Apr 2018 08:24:51 +0200,
    > Oleksandr Andrushchenko wrote:
    >> +static irqreturn_t evtchnl_interrupt_req(int irq, void *dev_id)
    >> +{
    >> + struct xen_snd_front_evtchnl *channel = dev_id;
    >> + struct xen_snd_front_info *front_info = channel->front_info;
    >> + struct xensnd_resp *resp;
    >> + RING_IDX i, rp;
    >> + unsigned long flags;
    >> +
    >> + if (unlikely(channel->state != EVTCHNL_STATE_CONNECTED))
    >> + return IRQ_HANDLED;
    >> +
    >> + spin_lock_irqsave(&front_info->io_lock, flags);
    >> +
    >> +again:
    >> + rp = channel->u.req.ring.sring->rsp_prod;
    >> + /* ensure we see queued responses up to rp */
    >> + rmb();
    >> +
    >> + for (i = channel->u.req.ring.rsp_cons; i != rp; i++) {
    > I'm not familiar with Xen stuff in general, but through a quick
    > glance, this kind of code worries me a bit.
    >
    > If channel->u.req.ring.rsp_cons has a bogus number, this may lead to a
    > very long loop, no? Better to have a sanity check of the ring buffer
    > size.
    In this loop I have:
    resp = RING_GET_RESPONSE(&channel->u.req.ring, i);
    and the RING_GET_RESPONSE macro is designed in the way that
    it wraps around when *i* in the question gets bigger than
    the ring size:

    #define RING_GET_REQUEST(_r, _idx)                    \
        (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req))

    So, even if the counter has a bogus number it will not last long

    >> +static irqreturn_t evtchnl_interrupt_evt(int irq, void *dev_id)
    >> +{
    >> + struct xen_snd_front_evtchnl *channel = dev_id;
    >> + struct xen_snd_front_info *front_info = channel->front_info;
    >> + struct xensnd_event_page *page = channel->u.evt.page;
    >> + u32 cons, prod;
    >> + unsigned long flags;
    >> +
    >> + if (unlikely(channel->state != EVTCHNL_STATE_CONNECTED))
    >> + return IRQ_HANDLED;
    >> +
    >> + spin_lock_irqsave(&front_info->io_lock, flags);
    >> +
    >> + prod = page->in_prod;
    >> + /* ensure we see ring contents up to prod */
    >> + virt_rmb();
    >> + if (prod == page->in_cons)
    >> + goto out;
    >> +
    >> + for (cons = page->in_cons; cons != prod; cons++) {
    > Ditto.
    Same as above
    >
    > thanks,
    >
    > Takashi
    Thank you,
    Oleksandr

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