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

Leon Romanovsky
2025-07-07T07:21:41Z

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

>
> Thanks,
> Abhijit
>
>