Re: [PATCH v3 10/14] RDMA/ionic: Register device ops for control path

Abhijit Gangurde
2025-07-07T14:56:34Z

On 7/7/25 12:51, Leon Romanovsky wrote:
> On Mon, Jul 07, 2025 at 10:57:13AM +0530, Abhijit Gangurde wrote:
>> On 7/4/25 22:38, Leon Romanovsky wrote:
>>> On Thu, Jul 03, 2025 at 12:49:30PM +0530, Abhijit Gangurde wrote:
>>>> On 7/2/25 23:30, Leon Romanovsky wrote:
>>>>> On Wed, Jul 02, 2025 at 10:18:03AM -0300, Jason Gunthorpe wrote:
>>>>>> On Tue, Jul 01, 2025 at 01:38:44PM +0300, Leon Romanovsky wrote:
>>>>>>>> +static void ionic_flush_qs(struct ionic_ibdev *dev)
>>>>>>>> +{
>>>>>>>> + struct ionic_qp *qp, *qp_tmp;
>>>>>>>> + struct ionic_cq *cq, *cq_tmp;
>>>>>>>> + LIST_HEAD(flush_list);
>>>>>>>> + unsigned long index;
>>>>>>>> +
>>>>>>>> + /* Flush qp send and recv */
>>>>>>>> + rcu_read_lock();
>>>>>>>> + xa_for_each(&dev->qp_tbl, index, qp) {
>>>>>>>> + kref_get(&qp->qp_kref);
>>>>>>>> + list_add_tail(&qp->ibkill_flush_ent, &flush_list);
>>>>>>>> + }
>>>>>>>> + rcu_read_unlock();
>>>>>>> Same question as for CQ. What does RCU lock protect here?
>>>>>> It should protect the kref_get against free of qp. The qp memory must
>>>>>> be RCU freed.
>>>>> I'm not sure that this was intension here. Let's wait for an answer from the author.
>>>> As Jason mentioned, It was intended to protect the kref_get against free of
>>>> cq and qp
>>>> in the destroy path.
>>> How is it possible? IB/core is supposed to protect from accessing verbs
>>> resources post their release/destroy.
>>>
>>> After you answered what RCU is protecting, I don't see why you would
>>> have custom kref over QP/CQ/e.t.c objects.
>>>
>>> Thanks
>> The RCU protected kref here is making sure that all the hw events are
>> processed before destroy callback returns. Similarly, when driver is
>> going for ib_unregister_device, it is draining the pending WRs and events.
> I asked why do you have kref in first place? When ib_unregister_device
> is called all "pending MR" already supposed to be destroyed.
>
> Thansk

The custom kref on QP/CQ object is holding the completion for the
destroy callback.
If any pending async hw events are being processed, destroy would wait
on this completion
before it returns.

Thanks