RE: [EXT] Re: [PATCH rdma-next 1/2] RDMA/qedr: Fix synchronization methods and memory leaks in qedr

[Michal Kalderon <mkalderon@marvell.com>]

> From: linux-rdma-owner@vger.kernel.org <linux-rdma-
> owner@vger.kernel.org> On Behalf Of Jason Gunthorpe
> 
> On Thu, Oct 03, 2019 at 07:33:00PM +0000, Michal Kalderon wrote:
> > > From: Jason Gunthorpe <jgg@ziepe.ca>
> > > Sent: Thursday, October 3, 2019 7:17 PM On Thu, Oct 03, 2019 at
> > > 03:03:41PM +0300, Michal Kalderon wrote:
> > >
> > > > diff --git a/drivers/infiniband/hw/qedr/qedr_iw_cm.c
> > > > b/drivers/infiniband/hw/qedr/qedr_iw_cm.c
> > > > index 22881d4442b9..ebc6bc25a0e2 100644
> > > > +++ b/drivers/infiniband/hw/qedr/qedr_iw_cm.c
> > > > @@ -79,6 +79,28 @@ qedr_fill_sockaddr6(const struct
> > > > qed_iwarp_cm_info
> > > *cm_info,
> > > >  	}
> > > >  }
> > > >
> > > > +static void qedr_iw_free_qp(struct kref *ref) {
> > > > +	struct qedr_qp *qp = container_of(ref, struct qedr_qp, refcnt);
> > > > +
> > > > +	xa_erase_irq(&qp->dev->qps, qp->qp_id);
> > >
> > > why is it _irq? Where are we in an irq when using the xa_lock on this
> xarray?
> > We could be under a spin lock when called from several locations in
> > core/iwcm.c
> 
> spinlock is OK, _irq is only needed if the code needs to mask IRQs because
> there is a user of the same lock in an IRQ context, see the documentation.
> 
> > > > @@ -516,8 +548,10 @@ int qedr_iw_connect(struct iw_cm_id *cm_id,
> > > struct iw_cm_conn_param *conn_param)
> > > >  		return -ENOMEM;
> > > >
> > > >  	ep->dev = dev;
> > > > +	kref_init(&ep->refcnt);
> > > > +
> > > > +	kref_get(&qp->refcnt);
> > >
> > > Here 'qp' comes out of an xa_load, but the QP is still visible in
> > > the xarray with a 0 refcount, so this is invalid.
> 
> > The core/iwcm takes a refcnt of the QP before calling connect, so it
> > can't be with refcnt zero
> 
> > > Also, the xa_load doesn't have any locking around it, so the entire
> > > thing looks wrong to me.
> > Since the functions calling it from core/iwcm ( connect / accept )
> > take a qp Ref-cnt before the calling there's no risk of the entry
> > being deleted while xa_load is called
> 
> Then why look it up in an xarray at all? If you already have the pointer to get a
> refcount then pass the refcounted pointer in and get rid of the sketchy
> xarray lookup.
> 
I don't have the pointer, the core/iwcm has the pointer. 
The interface between the core and driver is that the driver gets a qp number from
the core/iwcm and needs to get the QP pointer from it's database. All the iWARP drivers
are implemented this way, this is also not new to qedr. 

> I'm skeptical of this explanation
> 
> Jason