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

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Message-ID: <20250702180007.GK6278@unreal>
Date: Wed, 2 Jul 2025 21:00:07 +0300
From: Leon Romanovsky <leon@...nel.org>
To: Jason Gunthorpe <jgg@...pe.ca>
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 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.

> 
> But this pattern requires kref_get_unless_zero()
> 
> Jason