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

Abhijit Gangurde
2025-07-07T05:27:25Z

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.

Thanks,
Abhijit