Hi Adit,
Please see my comments inline.
Besides that I have no more comment for this patch.
Reviewed-by: Yuval Shaia <yuval.shaia@xxxxxxxxxx>
Yuval
On Thu, Sep 15, 2016 at 12:07:29AM +0000, Adit Ranadive wrote:
> On Wed, Sep 14, 2016 at 05:43:37 -0700, Yuval Shaia wrote:
> > On Sun, Sep 11, 2016 at 09:49:19PM -0700, Adit Ranadive wrote:
> > > +
> > > +static int pvrdma_poll_one(struct pvrdma_cq *cq, struct pvrdma_qp
> > **cur_qp,
> > > + struct ib_wc *wc)
> > > +{
> > > + struct pvrdma_dev *dev = to_vdev(cq->ibcq.device);
> > > + int has_data;
> > > + unsigned int head;
> > > + bool tried = false;
> > > + struct pvrdma_cqe *cqe;
> > > +
> > > +retry:
> > > + has_data = pvrdma_idx_ring_has_data(&cq->ring_state->rx,
> > > + cq->ibcq.cqe, &head);
> > > + if (has_data == 0) {
> > > + if (tried)
> > > + return -EAGAIN;
> > > +
> > > + /* Pass down POLL to give physical HCA a chance to poll. */
> > > + pvrdma_write_uar_cq(dev, cq->cq_handle |
> > PVRDMA_UAR_CQ_POLL);
> > > +
> > > + tried = true;
> > > + goto retry;
> > > + } else if (has_data == PVRDMA_INVALID_IDX) {
> >
> > I didn't went throw the entire life cycle of RX-ring's head and tail but you
> > need to make sure that PVRDMA_INVALID_IDX error is recoverable one, i.e
> > there is probability that in the next call to pvrdma_poll_one it will be fine.
> > Otherwise it is an endless loop.
>
> We have never run into this issue internally but I don't think we can recover here
I briefly reviewed the life cycle of RX-ring's head and tail and didn't
caught any suspicious place that might corrupt it.
So glad to see that you never encountered this case.
> in the driver. The only way to recover would be to destroy and recreate the CQ
> which we shouldn't do since it could be used by multiple QPs.
Agree.
But don't they hit the same problem too?
> We don't have a way yet to recover in the device. Once we add that this check
> should go away.
To be honest i have no idea how to do that - i was expecting driver's vendors
to come up with an ideas :)
I once came up with an idea to force restart of the driver but it was
rejected.
>
> The reason I returned an error value from poll_cq in v3 was to break the possible
> loop so that it might give clients a chance to recover. But since poll_cq is not expected
> to fail I just log the device error here. I can revert to that version if you want to break
> the possible loop.
Clients (ULPs) cannot recover from this case. They even do not check the
reason of the error and treats any error as -EAGAIN.
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