IB/mad: Agent registration is process context only

Document this (it's implicitly true due to sleeping operations already
in use in both registration and deregistration).  Use this fact to use
spin_lock_irq instead of spin_lock_irqsave.  This improves performance
slightly.
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/core/mad.c

@@ -190,6 +190,8 @@ EXPORT_SYMBOL(ib_response_mad);
 
 /*
  * ib_register_mad_agent - Register to send/receive MADs
+ *
+ * Context: Process context.
  */
 struct ib_mad_agent *ib_register_mad_agent(struct ib_device *device,
 					   u8 port_num,
@@ -210,7 +212,6 @@ struct ib_mad_agent *ib_register_mad_agent(struct ib_device *device,
 	struct ib_mad_mgmt_vendor_class *vendor_class;
 	struct ib_mad_mgmt_method_table *method;
 	int ret2, qpn;
-	unsigned long flags;
 	u8 mgmt_class, vclass;
 
 	/* Validate parameters */
@@ -376,7 +377,7 @@ struct ib_mad_agent *ib_register_mad_agent(struct ib_device *device,
 		goto error4;
 	}
 
-	spin_lock_irqsave(&port_priv->reg_lock, flags);
+	spin_lock_irq(&port_priv->reg_lock);
 	mad_agent_priv->agent.hi_tid = atomic_inc_return(&ib_mad_client_id);
 
 	/*
@@ -422,11 +423,11 @@ struct ib_mad_agent *ib_register_mad_agent(struct ib_device *device,
 
 	/* Add mad agent into port's agent list */
 	list_add_tail(&mad_agent_priv->agent_list, &port_priv->agent_list);
-	spin_unlock_irqrestore(&port_priv->reg_lock, flags);
+	spin_unlock_irq(&port_priv->reg_lock);
 
 	return &mad_agent_priv->agent;
 error5:
-	spin_unlock_irqrestore(&port_priv->reg_lock, flags);
+	spin_unlock_irq(&port_priv->reg_lock);
 	ib_mad_agent_security_cleanup(&mad_agent_priv->agent);
 error4:
 	kfree(reg_req);
@@ -575,7 +576,6 @@ static inline void deref_snoop_agent(struct ib_mad_snoop_private *mad_snoop_priv
 static void unregister_mad_agent(struct ib_mad_agent_private *mad_agent_priv)
 {
 	struct ib_mad_port_private *port_priv;
-	unsigned long flags;
 
 	/* Note that we could still be handling received MADs */
 
@@ -587,10 +587,10 @@ static void unregister_mad_agent(struct ib_mad_agent_private *mad_agent_priv)
 	port_priv = mad_agent_priv->qp_info->port_priv;
 	cancel_delayed_work(&mad_agent_priv->timed_work);
 
-	spin_lock_irqsave(&port_priv->reg_lock, flags);
+	spin_lock_irq(&port_priv->reg_lock);
 	remove_mad_reg_req(mad_agent_priv);
 	list_del(&mad_agent_priv->agent_list);
-	spin_unlock_irqrestore(&port_priv->reg_lock, flags);
+	spin_unlock_irq(&port_priv->reg_lock);
 
 	flush_workqueue(port_priv->wq);
 	ib_cancel_rmpp_recvs(mad_agent_priv);
@@ -625,6 +625,8 @@ static void unregister_mad_snoop(struct ib_mad_snoop_private *mad_snoop_priv)
 
 /*
  * ib_unregister_mad_agent - Unregisters a client from using MAD services
+ *
+ * Context: Process context.
  */
 void ib_unregister_mad_agent(struct ib_mad_agent *mad_agent)
 {