Subject: Re: [PATCH 05/11] IB/cm: Share listening CM IDs

From: Haggai Eran <haggaie-VPRAkNaXOzVWk0Htik3J/[email-masked]>
Date: Tue, 16 Jun 2015 15:50:39 +0300

On 16/06/2015 01:13, Hefty, Sean wrote:
>> @@ -722,6 +725,7 @@ struct ib_cm_id *ib_create_cm_id(struct ib_device
>> *device,
>>  	INIT_LIST_HEAD(&cm_id_priv->work_list);
>>  	atomic_set(&cm_id_priv->work_count, -1);
>>  	atomic_set(&cm_id_priv->refcount, 1);
>> +	cm_id_priv->listen_sharecount = 1;
> 
> This is setting the listen count before we know whether the cm_id will actually be used to listen.

Right. I'll move it to the new_id case in ib_cm_id_create_and_listen.

> 
> 
>>  	return &cm_id_priv->id;
>>
>>  error:
>> @@ -847,11 +851,21 @@ retest:
>>  	spin_lock_irq(&cm_id_priv->lock);
>>  	switch (cm_id->state) {
>>  	case IB_CM_LISTEN:
>> -		cm_id->state = IB_CM_IDLE;
>>  		spin_unlock_irq(&cm_id_priv->lock);
>> +
>>  		spin_lock_irq(&cm.lock);
>> +		if (--cm_id_priv->listen_sharecount > 0) {
>> +			/* The id is still shared. */
>> +			atomic_dec(&cm_id_priv->refcount);
>> +			spin_unlock_irq(&cm.lock);
>> +			return;
>> +		}
>>  		rb_erase(&cm_id_priv->service_node, &cm.listen_service_table);
>>  		spin_unlock_irq(&cm.lock);
>> +
>> +		spin_lock_irq(&cm_id_priv->lock);
>> +		cm_id->state = IB_CM_IDLE;
>> +		spin_unlock_irq(&cm_id_priv->lock);
> 
> Why is the state being changed?  The cm_id is about to be freed anyway.

It matches the rest of the code, but I don't think it is actually being
used for listening ids. I will drop it.

> 
> 
>>  		break;
>>  	case IB_CM_SIDR_REQ_SENT:
>>  		cm_id->state = IB_CM_IDLE;
>> @@ -929,11 +943,32 @@ void ib_destroy_cm_id(struct ib_cm_id *cm_id)
>>  }
>>  EXPORT_SYMBOL(ib_destroy_cm_id);
>>
>> -int ib_cm_listen(struct ib_cm_id *cm_id, __be64 service_id, __be64
>> service_mask,
>> -		 struct ib_cm_compare_data *compare_data)
>> +/**
>> + * __ib_cm_listen - Initiates listening on the specified service ID for
>> + *   connection and service ID resolution requests.
>> + * @cm_id: Connection identifier associated with the listen request.
>> + * @service_id: Service identifier matched against incoming connection
>> + *   and service ID resolution requests.  The service ID should be
>> specified
>> + *   network-byte order.  If set to IB_CM_ASSIGN_SERVICE_ID, the CM will
>> + *   assign a service ID to the caller.
>> + * @service_mask: Mask applied to service ID used to listen across a
>> + *   range of service IDs.  If set to 0, the service ID is matched
>> + *   exactly.  This parameter is ignored if %service_id is set to
>> + *   IB_CM_ASSIGN_SERVICE_ID.
>> + * @compare_data: This parameter is optional.  It specifies data that
>> must
>> + *   appear in the private data of a connection request for the specified
>> + *   listen request.
>> + * @lock: If set, lock the cm.lock spin-lock when adding the id to the
>> + *   listener tree. When false, the caller must already hold the spin-
>> lock,
>> + *   and compare_data must be NULL.
>> + */
>> +static int __ib_cm_listen(struct ib_cm_id *cm_id, __be64 service_id,
>> +			  __be64 service_mask,
>> +			  struct ib_cm_compare_data *compare_data,
>> +			  bool lock)
>>  {
>>  	struct cm_id_private *cm_id_priv, *cur_cm_id_priv;
>> -	unsigned long flags;
>> +	unsigned long flags = 0;
>>  	int ret = 0;
>>
>>  	service_mask = service_mask ? service_mask : ~cpu_to_be64(0);
>> @@ -959,7 +994,8 @@ int ib_cm_listen(struct ib_cm_id *cm_id, __be64
>> service_id, __be64 service_mask,
>>
>>  	cm_id->state = IB_CM_LISTEN;
>>
>> -	spin_lock_irqsave(&cm.lock, flags);
>> +	if (lock)
>> +		spin_lock_irqsave(&cm.lock, flags);
> 
> I'm not a fan of this sort of locking structure.  Why not just move the locking into the outside calls completely?  I.e. move to ib_cm_listen() instead of passing in true.

The reason is that this function can sleep when called compare_data !=
NULL, allocating the id's compare_data with GFP_KERNEL. But, since the
compare_data is going away in a later patch, I can actually fix the
locking at that point. I'll change the patch that removes compare_data
to also remove the lock parameter.

> 
> 
>>  	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);
>> @@ -968,7 +1004,8 @@ 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;
>> @@ -978,8 +1015,86 @@ int ib_cm_listen(struct ib_cm_id *cm_id, __be64
>> service_id, __be64 service_mask,
>>  	}
>>  	return ret;
>>  }
>> +
>> +int ib_cm_listen(struct ib_cm_id *cm_id, __be64 service_id, __be64
>> service_mask,
>> +		 struct ib_cm_compare_data *compare_data)
>> +{
>> +	return __ib_cm_listen(cm_id, service_id, service_mask, compare_data,
>> +			      true);
>> +}
>>  EXPORT_SYMBOL(ib_cm_listen);
>>
>> +/**
>> + * Create a new listening ib_cm_id and listen on the given service ID.
>> + *
>> + * If there's an existing ID listening on that same device and service
>> ID,
>> + * return it.
>> + *
>> + * @device: Device associated with the cm_id.  All related communication
>> will
>> + * be associated with the specified device.
>> + * @cm_handler: Callback invoked to notify the user of CM events.
>> + * @service_id: Service identifier matched against incoming connection
>> + *   and service ID resolution requests.  The service ID should be
>> specified
>> + *   network-byte order.  If set to IB_CM_ASSIGN_SERVICE_ID, the CM will
>> + *   assign a service ID to the caller.
>> + * @service_mask: Mask applied to service ID used to listen across a
>> + *   range of service IDs.  If set to 0, the service ID is matched
>> + *   exactly.  This parameter is ignored if %service_id is set to
>> + *   IB_CM_ASSIGN_SERVICE_ID.
>> + *
>> + * Callers should call ib_destroy_cm_id when done with the listener ID.
>> + */
>> +struct ib_cm_id *ib_cm_id_create_and_listen(
> 
> Maybe ib_cm_insert_listen() instead?

Okay.

> 
>> +		struct ib_device *device,
>> +		ib_cm_handler cm_handler,
>> +		__be64 service_id,
>> +		__be64 service_mask)
>> +{
>> +	struct cm_id_private *cm_id_priv;
>> +	struct ib_cm_id *cm_id;
>> +	unsigned long flags;
>> +	int err = 0;
>> +
>> +	/* Create an ID in advance, since the creation may sleep */
>> +	cm_id = ib_create_cm_id(device, cm_handler, NULL);
>> +	if (IS_ERR(cm_id))
>> +		return cm_id;
>> +
>> +	spin_lock_irqsave(&cm.lock, flags);
>> +
>> +	if (service_id == IB_CM_ASSIGN_SERVICE_ID)
>> +		goto new_id;
>> +
>> +	/* Find an existing ID */
>> +	cm_id_priv = cm_find_listen(device, service_id, NULL);
>> +	if (cm_id_priv) {
>> +		atomic_inc(&cm_id_priv->refcount);
>> +		++cm_id_priv->listen_sharecount;
>> +		spin_unlock_irqrestore(&cm.lock, flags);
>> +
>> +		ib_destroy_cm_id(cm_id);
>> +		cm_id = &cm_id_priv->id;
>> +		if (cm_id->cm_handler != cm_handler || cm_id->context)
>> +			/* Sharing an ib_cm_id with different handlers is not
>> +			 * supported */
>> +			return ERR_PTR(-EINVAL);
> 
> This leaks listen_sharecount references.

Thanks. I'll fix that.

> 
> 
>> +		return cm_id;
>> +	}
>> +
>> +new_id:
>> +	/* Use newly created ID */
>> +	err = __ib_cm_listen(cm_id, service_id, service_mask, NULL, false);
>> +
>> +	spin_unlock_irqrestore(&cm.lock, flags);
>> +
>> +	if (err) {
>> +		ib_destroy_cm_id(cm_id);
>> +		return ERR_PTR(err);
>> +	}
>> +	return cm_id;
>> +}
>> +EXPORT_SYMBOL(ib_cm_id_create_and_listen);

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