Re: [PATCH 07/13] IB: add a proper completion queue abstraction

From: Parav Pandit
Date: Fri Jan 15 2016 - 08:54:10 EST

Hi Christoph, Sagi,

On Tue, Dec 8, 2015 at 2:21 AM, Christoph Hellwig <hch@xxxxxx> wrote:

> +static void ib_cq_poll_work(struct work_struct *work)
> +{
> + struct ib_cq *cq = container_of(work, struct ib_cq, work);
> + int completed;
> +
> + completed = __ib_process_cq(cq, IB_POLL_BUDGET_WORKQUEUE);
> + if (completed >= IB_POLL_BUDGET_WORKQUEUE ||
> + ib_req_notify_cq(cq, IB_POLL_FLAGS) > 0)
> + queue_work(ib_comp_wq, &cq->work);
> +}

In above code, Let says completion is added in a time window where
ib_process_cq is completed (CQ is diarmed in hw at that point) and
ib_req_notify_cq is yet to be called.
Provider vendor driver say mlx4 or mlx5 as specific case always
returns ib_req_notify_cq = 0.
Will it result into a missed notification? (so queue_work is not done).

IB spec says: Any CQ entries that existed before the notify is enabled
will not result in a call to the handler.

I did try to follow this thread on similar notes.

I believe above code possibly needs fix based above two comments? Or I
must be missing something basic here.