linux-kernel - Re: [PATCH rdma-rc v2] RDMA/core: Simplify addition of restrack object

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Date:   Sun, 27 Jun 2021 11:07:33 +0300
From:   Leon Romanovsky <leon@...nel.org>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Doug Ledford <dledford@...hat.com>, linux-kernel@...r.kernel.org,
        linux-rdma@...r.kernel.org, Pavel Skripkin <paskripkin@...il.com>,
        Shay Drory <shayd@...dia.com>
Subject: Re: [PATCH rdma-rc v2] RDMA/core: Simplify addition of restrack
 object

On Thu, Jun 24, 2021 at 02:48:41PM -0300, Jason Gunthorpe wrote:
> On Tue, Jun 08, 2021 at 08:23:48AM +0300, Leon Romanovsky wrote:
> > From: Leon Romanovsky <leonro@...dia.com>
> > 
> > Change location of rdma_restrack_add() callers to be near attachment
> > to device logic. Such improvement fixes the bug where task_struct was
> > acquired but not released, causing to resource leak.
> > 
> >   ucma_create_id() {
> >     ucma_alloc_ctx();
> >     rdma_create_user_id() {
> >       rdma_restrack_new();
> >       rdma_restrack_set_name() {
> >         rdma_restrack_attach_task.part.0(); <--- task_struct was gotten
> >       }
> >     }
> >     ucma_destroy_private_ctx() {
> >       ucma_put_ctx();
> >       rdma_destroy_id() {
> >         _destroy_id()                       <--- id_priv was freed
> >       }
> >     }
> >   }
> 
> I still don't understand this patch
> 
> > @@ -1852,6 +1849,7 @@ static void _destroy_id(struct rdma_id_private *id_priv,
> >  {
> >  	cma_cancel_operation(id_priv, state);
> >  
> > +	rdma_restrack_del(&id_priv->res);
> >  	if (id_priv->cma_dev) {
> >  		if (rdma_cap_ib_cm(id_priv->id.device, 1)) {
> >  			if (id_priv->cm_id.ib)
> > @@ -1861,7 +1859,6 @@ static void _destroy_id(struct rdma_id_private *id_priv,
> >  				iw_destroy_cm_id(id_priv->cm_id.iw);
> >  		}
> >  		cma_leave_mc_groups(id_priv);
> > -		rdma_restrack_del(&id_priv->res);
> >  		cma_release_dev(id_priv);
> 
> This seems to be the only hunk that is actually necessary, ensuring a
> non-added ID is always cleaned up is the necessary step to fixing the
> trace above.
> 
> What is the rest of this doing?? It looks wrong:
> 
> int rdma_bind_addr(struct rdma_cm_id *id, struct sockaddr *addr)
> {
> [..]
> 	ret = cma_get_port(id_priv);
> 	if (ret)
> 		goto err2;
> err2:
> [..]
> 	if (!cma_any_addr(addr))
> 		rdma_restrack_del(&id_priv->res);
> 
> Which means if rdma_bind_addr() fails then restrack will discard the
> task, even though the cm_id is still valid! The ucma is free to try
> bind again and keep using the ID.

"Failure to bind" means that cma_attach_to_dev() needs to be unwind.

It is the same if rdma_restrack_add() inside that function like in this
patch or in the line before rdma_bind_addr() returns as it was in
previous code.

Thanks

> 
> Jason