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

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Date:   Thu, 24 Jun 2021 14:48:41 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     Doug Ledford <dledford@...hat.com>,
        Leon Romanovsky <leonro@...dia.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 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.

Jason