[RFC] IB/mad: Use IDR instead of per-port list

[Matthew Wilcox]

Hans reports a bug where the mlx4 driver uses the MSB of the agent number
to store slave number, meaning we can only use agent numbers up to 2^24.
Fix this by using an IDR to assign the agent numbers and also look up the
agent when a MSD packet is received.

I've changed the locking substantially, so this may well have a
performance issue.  There are a few different possibilities for fixing
that, including moving to an RCU-based lookup.


diff --git a/drivers/infiniband/core/mad.c b/drivers/infiniband/core/mad.c
index b28452a55a08..611a1f268b07 100644
--- a/drivers/infiniband/core/mad.c
+++ b/drivers/infiniband/core/mad.c
@@ -38,6 +38,7 @@
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/dma-mapping.h>
+#include <linux/idr.h>
 #include <linux/slab.h>
 #include <linux/module.h>
 #include <linux/security.h>
@@ -58,8 +59,8 @@ MODULE_PARM_DESC(send_queue_size, "Size of send queue in number of work requests
 module_param_named(recv_queue_size, mad_recvq_size, int, 0444);
 MODULE_PARM_DESC(recv_queue_size, "Size of receive queue in number of work requests");
 
+static DEFINE_IDR(ib_mad_clients);
 static struct list_head ib_mad_port_list;
-static atomic_t ib_mad_client_id = ATOMIC_INIT(0);
 
 /* Port list lock */
 static DEFINE_SPINLOCK(ib_mad_port_list_lock);
@@ -376,8 +377,16 @@ struct ib_mad_agent *ib_register_mad_agent(struct ib_device *device,
 		goto error4;
 	}
 
-	spin_lock_irqsave(&port_priv->reg_lock, flags);
-	mad_agent_priv->agent.hi_tid = atomic_inc_return(&ib_mad_client_id);
+	idr_preload(GFP_KERNEL);
+	idr_lock_irqsave(&ib_mad_clients, flags);
+
+	ret2 = idr_alloc_cyclic(&ib_mad_clients, mad_agent_priv, 0,
+			(1 << 24), GFP_ATOMIC);
+	if (ret2 < 0) {
+		ret = ERR_PTR(ret2);
+		goto error5;
+	}
+	mad_agent_priv->agent.hi_tid = ret2;
 
 	/*
 	 * Make sure MAD registration (if supplied)
@@ -393,7 +402,7 @@ struct ib_mad_agent *ib_register_mad_agent(struct ib_device *device,
 				if (method) {
 					if (method_in_use(&method,
 							   mad_reg_req))
-						goto error5;
+						goto error6;
 				}
 			}
 			ret2 = add_nonoui_reg_req(mad_reg_req, mad_agent_priv,
@@ -409,24 +418,26 @@ struct ib_mad_agent *ib_register_mad_agent(struct ib_device *device,
 					if (is_vendor_method_in_use(
 							vendor_class,
 							mad_reg_req))
-						goto error5;
+						goto error6;
 				}
 			}
 			ret2 = add_oui_reg_req(mad_reg_req, mad_agent_priv);
 		}
 		if (ret2) {
 			ret = ERR_PTR(ret2);
-			goto error5;
+			goto error6;
 		}
 	}
 
-	/* 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);
+	idr_unlock_irqrestore(&ib_mad_clients, flags);
+	idr_preload_end();
 
 	return &mad_agent_priv->agent;
+error6:
+	idr_remove(&ib_mad_clients, mad_agent_priv->agent.hi_tid);
 error5:
-	spin_unlock_irqrestore(&port_priv->reg_lock, flags);
+	idr_unlock_irqrestore(&ib_mad_clients, flags);
+	idr_preload_end();
 	ib_mad_agent_security_cleanup(&mad_agent_priv->agent);
 error4:
 	kfree(reg_req);
@@ -587,10 +598,10 @@ 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);
+	idr_lock_irqsave(&ib_mad_clients, flags);
 	remove_mad_reg_req(mad_agent_priv);
-	list_del(&mad_agent_priv->agent_list);
-	spin_unlock_irqrestore(&port_priv->reg_lock, flags);
+	idr_remove(&ib_mad_clients, mad_agent_priv->agent.hi_tid);
+	idr_unlock_irqrestore(&ib_mad_clients, flags);
 
 	flush_workqueue(port_priv->wq);
 	ib_cancel_rmpp_recvs(mad_agent_priv);
@@ -1718,22 +1729,16 @@ find_mad_agent(struct ib_mad_port_private *port_priv,
 	struct ib_mad_agent_private *mad_agent = NULL;
 	unsigned long flags;
 
-	spin_lock_irqsave(&port_priv->reg_lock, flags);
+	idr_lock_irqsave(&ib_mad_clients, flags);
 	if (ib_response_mad(mad_hdr)) {
 		u32 hi_tid;
-		struct ib_mad_agent_private *entry;
 
 		/*
 		 * Routing is based on high 32 bits of transaction ID
 		 * of MAD.
 		 */
 		hi_tid = be64_to_cpu(mad_hdr->tid) >> 32;
-		list_for_each_entry(entry, &port_priv->agent_list, agent_list) {
-			if (entry->agent.hi_tid == hi_tid) {
-				mad_agent = entry;
-				break;
-			}
-		}
+		mad_agent = idr_find(&ib_mad_clients, hi_tid);
 	} else {
 		struct ib_mad_mgmt_class_table *class;
 		struct ib_mad_mgmt_method_table *method;
@@ -1794,7 +1799,7 @@ find_mad_agent(struct ib_mad_port_private *port_priv,
 		}
 	}
 out:
-	spin_unlock_irqrestore(&port_priv->reg_lock, flags);
+	idr_unlock_irqrestore(&ib_mad_clients, flags);
 
 	return mad_agent;
 }
@@ -3156,8 +3161,6 @@ static int ib_mad_port_open(struct ib_device *device,
 
 	port_priv->device = device;
 	port_priv->port_num = port_num;
-	spin_lock_init(&port_priv->reg_lock);
-	INIT_LIST_HEAD(&port_priv->agent_list);
 	init_mad_qp(port_priv, &port_priv->qp_info[0]);
 	init_mad_qp(port_priv, &port_priv->qp_info[1]);
 
@@ -3336,6 +3339,9 @@ int ib_mad_init(void)
 
 	INIT_LIST_HEAD(&ib_mad_port_list);
 
+	/* Client ID 0 is used for snoop-only clients */
+	idr_alloc(&ib_mad_clients, NULL, 0, 0, GFP_KERNEL);
+
 	if (ib_register_client(&mad_client)) {
 		pr_err("Couldn't register ib_mad client\n");
 		return -EINVAL;
diff --git a/drivers/infiniband/core/mad_priv.h b/drivers/infiniband/core/mad_priv.h
index 28669f6419e1..f2cb2eea7d42 100644
--- a/drivers/infiniband/core/mad_priv.h
+++ b/drivers/infiniband/core/mad_priv.h
@@ -89,7 +89,6 @@ struct ib_rmpp_segment {
 };
 
 struct ib_mad_agent_private {
-	struct list_head agent_list;
 	struct ib_mad_agent agent;
 	struct ib_mad_reg_req *reg_req;
 	struct ib_mad_qp_info *qp_info;
@@ -201,9 +200,7 @@ struct ib_mad_port_private {
 	struct ib_cq *cq;
 	struct ib_pd *pd;
 
-	spinlock_t reg_lock;
 	struct ib_mad_mgmt_version_table version[MAX_MGMT_VERSION];
-	struct list_head agent_list;
 	struct workqueue_struct *wq;
 	struct ib_mad_qp_info qp_info[IB_MAD_QPS_CORE];
 };
diff --git a/include/linux/idr.h b/include/linux/idr.h
index e856f4e0ab35..97b4924f0bca 100644
--- a/include/linux/idr.h
+++ b/include/linux/idr.h
@@ -81,6 +81,11 @@ static inline void idr_set_cursor(struct idr *idr, unsigned int val)
 	WRITE_ONCE(idr->idr_next, val);
 }
 
+#define idr_lock_irqsave(idr, flags) \
+				xa_lock_irqsave(&(idr)->idr_rt, flags)
+#define idr_unlock_irqrestore(idr, flags) \
+				xa_unlock_irqrestore(&(idr)->idr_rt, flags)
+
 /**
  * DOC: idr sync
  * idr synchronization (stolen from radix-tree.h)