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

[Leon Romanovsky <leon@kernel.org>]

On Mon, Jul 07, 2025 at 08:26:20PM +0530, Abhijit Gangurde wrote:
> 
> 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.

Please see how other drivers avoid such situation. There is no need in
custom kref.

Thanks

> 
> Thanks
>