netdev - Re: [PATCH v1 05/12] IB/cm: Share listening CM IDs

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Date:	Mon, 13 Jul 2015 11:48:37 -0600
From:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:	Haggai Eran <haggaie@...lanox.com>
Cc:	Doug Ledford <dledford@...hat.com>, linux-rdma@...r.kernel.org,
	netdev@...r.kernel.org, Liran Liss <liranl@...lanox.com>,
	Guy Shapiro <guysh@...lanox.com>,
	Shachar Raindel <raindel@...lanox.com>,
	Yotam Kenneth <yotamke@...lanox.com>
Subject: Re: [PATCH v1 05/12] IB/cm: Share listening CM IDs

On Mon, Jun 22, 2015 at 03:42:34PM +0300, Haggai Eran wrote:
>  		spin_lock_irq(&cm.lock);
> +		if (--cm_id_priv->listen_sharecount > 0) {
> +			/* The id is still shared. */
> +			atomic_dec(&cm_id_priv->refcount);

Nit: This looks very strange not to be cm_deref_id .. Looks OK as is
because we are sure refcount cannot be 0 here?

> @@ -958,8 +988,10 @@ int ib_cm_listen(struct ib_cm_id *cm_id, __be64 service_id, __be64 service_mask,
>  	}
>  
>  	cm_id->state = IB_CM_LISTEN;
> +	++cm_id_priv->listen_sharecount;
>
> -	spin_lock_irqsave(&cm.lock, flags);
> +	if (lock)
> +		spin_lock_irqsave(&cm.lock, flags);

Hmm, I'd like to see the listen_sharecount consistently locked, so it
should be manipulated only while cm.lock is held..

>  	if (service_id == IB_CM_ASSIGN_SERVICE_ID) {
>  		cm_id->service_id = cpu_to_be64(cm.listen_service_id++);
>  		cm_id->service_mask = ~cpu_to_be64(0);
> @@ -968,18 +1000,98 @@ int ib_cm_listen(struct ib_cm_id *cm_id, __be64 service_id, __be64 service_mask,
>  		cm_id->service_mask = service_mask;
>  	}
>  	cur_cm_id_priv = cm_insert_listen(cm_id_priv);
> -	spin_unlock_irqrestore(&cm.lock, flags);
> +	if (lock)
> +		spin_unlock_irqrestore(&cm.lock, flags);
>  
>  	if (cur_cm_id_priv) {
>  		cm_id->state = IB_CM_IDLE;
> +		--cm_id_priv->listen_sharecount;

Ditto

Otherwise I don't see any other mechanical problems with this. Sean
said he was happy with the idea right?

Reviewed-By: Jason Gunthorpe <jgunthorpe@...idianresearch.com>

Jason
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