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

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Message-ID: <20250702131803.GB904431@ziepe.ca>
Date: Wed, 2 Jul 2025 10:18:03 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Leon Romanovsky <leon@...nel.org>
Cc: Abhijit Gangurde <abhijit.gangurde@....com>, shannon.nelson@....com,
	brett.creeley@....com, davem@...emloft.net, edumazet@...gle.com,
	kuba@...nel.org, pabeni@...hat.com, corbet@....net,
	andrew+netdev@...n.ch, allen.hubbe@....com, nikhil.agarwal@....com,
	linux-rdma@...r.kernel.org, netdev@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	Andrew Boyer <andrew.boyer@....com>
Subject: Re: [PATCH v3 10/14] RDMA/ionic: Register device ops for control path

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.

But this pattern requires kref_get_unless_zero()

Jason